chap-snippets.lyx

#LyX 1.6.7 created this file. For more info see http://www.lyx.org/
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\quotes_language english
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\author "" 
\author "" 
\end_header

\begin_body

\begin_layout Chapter
Snippets
\begin_inset Index
status open

\begin_layout Plain Layout
Snippets
\end_layout

\end_inset


\begin_inset CommandInset label
LatexCommand label
name "cha:Snippets"

\end_inset


\end_layout

\begin_layout Standard
Put simply, a snippet is a Scala method that transforms input XML into output
 XML
\begin_inset Index
status open

\begin_layout Plain Layout
XML
\end_layout

\end_inset

.
 Snippets act as independent (or dependent, if you want) pieces of logic
 that you insert into your page to perform rendering.
 As such, snippets form the backbone of Lift's View-First
\begin_inset Index
status open

\begin_layout Plain Layout
View-First
\end_layout

\end_inset

 rendering architecture.
 Although snippets aren't the only mechanism Lift has for rendering page
 views (see Views, Section 
\begin_inset CommandInset ref
LatexCommand vref
reference "sec:Views"

\end_inset

, Custom Dispatch, Section 
\begin_inset CommandInset ref
LatexCommand vref
reference "sec:Custom-dispatch-func"

\end_inset

, or even the REST API, Chapter 
\begin_inset CommandInset ref
LatexCommand ref
reference "cha:Web-Services"

\end_inset

), they're so widely used and so important that we feel they warrant their
 own chapter.
\end_layout

\begin_layout Standard
In this chapter we will cover the ins and outs of snippets, from the snippet
 tag that you place in your templates, through how the snippet method is
 resolved, to the snippet method definition itself.
 We'll also cover related topics and some advanced functionality in snippets
 for those looking to push Lift's boundaries.
\end_layout

\begin_layout Section
The Snippet Tag
\begin_inset Index
status open

\begin_layout Plain Layout
snippet
\end_layout

\end_inset


\begin_inset Index
status open

\begin_layout Plain Layout
Tags ! snippet
\end_layout

\end_inset


\begin_inset CommandInset label
LatexCommand label
name "sec:The-Snippet-Tag"

\end_inset


\begin_inset CommandInset label
LatexCommand label
name "sub:snippet-tag"

\end_inset


\end_layout

\begin_layout LyX-Code

\family typewriter
Usage: <lift:snippet type="snippetName" ...options...
 />
\end_layout

\begin_layout LyX-Code
       <lift:snippetName ...options...
 />
\end_layout

\begin_layout LyX-Code
       <div class=
\begin_inset Quotes erd
\end_inset

lift:snippetName?opt1=...;opt2=...;opt3=...
\begin_inset Quotes erd
\end_inset

 />
\end_layout

\begin_layout Standard
The snippet tag is what you use to tell Lift where and how to invoke a snippet
 method on given XML content.
 The most important part of the tag is the snippet name, which is used to
 resolve which snippet method will process the snippet tag contents.
 We'll cover how the snippet name is resolved to a concrete method in section
 
\begin_inset CommandInset ref
LatexCommand ref
reference "sub:Snippet-Dispatch"

\end_inset

.
 
\end_layout

\begin_layout Standard
\align center
\begin_inset Box Shadowbox
position "t"
hor_pos "c"
has_inner_box 1
inner_pos "t"
use_parbox 0
width "75col%"
special "none"
height "1in"
height_special "totalheight"
status open

\begin_layout Plain Layout
Note that there is a shorthand for the 
\family typewriter
type
\family default
 attribute simply by appending the snippet name after the 
\family typewriter
lift:
\family default
 prefix.
 If you use this shorthand, make sure to avoid naming your snippets the
 same as Lift's built-in tags, such as 
\family typewriter
surround
\family default
, 
\family typewriter
children
\family default
, 
\family typewriter
embed
\family default
, etc.
\end_layout

\end_inset


\end_layout

\begin_layout Standard
In addition to the the 
\family typewriter
type
\family default
 attribute, Lift will process several other options:
\end_layout

\begin_layout Description
form If the 
\family typewriter
form
\begin_inset Index
status open

\begin_layout Plain Layout
Forms ! snippet tag
\end_layout

\end_inset


\family default
 attribute is included with a value of either 
\begin_inset Quotes eld
\end_inset

POST
\begin_inset Quotes erd
\end_inset

 or 
\begin_inset Quotes eld
\end_inset

GET
\begin_inset Quotes erd
\end_inset

, then an appropriate form tag will be emitted into the XHTML using the
 specified submission method.
 If you omit this tag from a snippet that generates a form, the form elements
 will display but the form won't submit.
\end_layout

\begin_layout Description
multipart 
\begin_inset Index
status open

\begin_layout Plain Layout
Forms ! multipart
\end_layout

\end_inset


\begin_inset Index
status open

\begin_layout Plain Layout
Forms ! file upload
\end_layout

\end_inset

The 
\family typewriter
multipart
\family default
 attribute is a boolean (the default is false, specify 
\begin_inset Quotes eld
\end_inset

yes
\begin_inset Quotes erd
\end_inset

, 
\begin_inset Quotes eld
\end_inset

true
\begin_inset Quotes erd
\end_inset

 or 
\begin_inset Quotes eld
\end_inset

1
\begin_inset Quotes erd
\end_inset

 to enable) that specifies whether a generated form tag should be set to
 use multipart form submission.
 This is most typically used for file uploads (Section 
\begin_inset CommandInset ref
LatexCommand ref
reference "sec:File-Uploads"

\end_inset

).
 If you don't also specify the 
\family typewriter
form
\family default
 attribute then this won't do anything.
\end_layout

\begin_layout Description
eager_eval 
\begin_inset Index
status open

\begin_layout Plain Layout
Snippets ! eager_eval
\end_layout

\end_inset

The eager_eval attribute is a boolean (the default is false, specify 
\begin_inset Quotes eld
\end_inset

yes
\begin_inset Quotes erd
\end_inset

, 
\begin_inset Quotes eld
\end_inset

true
\begin_inset Quotes erd
\end_inset

 or 
\begin_inset Quotes eld
\end_inset

1
\begin_inset Quotes erd
\end_inset

 to enable) that controls the order of processing for the snippet tag contents.
 Normally, the snippet is processed and then the XML returned from the snippet
 is further processed for Lift tags.
 Enabling eager_eval reverses this order so that the contents of the snippet
 tag are processed first.
 We cover this in more detail with an example in Section 
\begin_inset CommandInset ref
LatexCommand ref
reference "sub:Eager-Eval"

\end_inset

.
\end_layout

\begin_layout Standard
With Lift 2.2's Designer-Friendly Templates (Section 
\begin_inset CommandInset ref
LatexCommand vref
reference "sec:Designer-Friendly-Templates"

\end_inset

), you can also specify a snippet tag as part of the class attribute for
 a given element.
 Attributes for snippets invoked in this manner are passed via a query string.
 Listing 
\begin_inset CommandInset ref
LatexCommand ref
reference "lst:Invoking-Snippets-Via-Class"

\end_inset

 shows an example of how we can use the standard 
\family typewriter
lift:surround
\family default
 processing by modiying the 
\family typewriter
class
\family default
 of our content element.
\end_layout

\begin_layout Standard
\begin_inset listings
inline false
status open

\begin_layout Plain Layout

\begin_inset Caption

\begin_layout Plain Layout

Invoking Snippets Via the Class Attribute
\begin_inset CommandInset label
LatexCommand label
name "lst:Invoking-Snippets-Via-Class"

\end_inset


\end_layout

\end_inset


\end_layout

\begin_layout Plain Layout

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" 
\end_layout

\begin_layout Plain Layout

    "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
\end_layout

\begin_layout Plain Layout

 <html xmlns="http://www.w3.org/1999/xhtml">
\end_layout

\begin_layout Plain Layout

   <head>
\end_layout

\begin_layout Plain Layout

	<title>Not really</title>
\end_layout

\begin_layout Plain Layout

   </head>
\end_layout

\begin_layout Plain Layout

   <body class="lift:content_id=real_content">
\end_layout

\begin_layout Plain Layout

     <div class="lift:surround?with=default;at=content" id="real_content">
\end_layout

\begin_layout Plain Layout

       <h1>Welcome to your project!</h1>
\end_layout

\begin_layout Plain Layout

     </div>
\end_layout

\begin_layout Plain Layout

   </body>
\end_layout

\begin_layout Plain Layout

 </html>
\end_layout

\end_inset


\end_layout

\begin_layout Section
Snippet Dispatch
\begin_inset CommandInset label
LatexCommand label
name "sub:Snippet-Dispatch"

\end_inset


\begin_inset Index
status open

\begin_layout Plain Layout
Snippets ! Dispatch
\end_layout

\end_inset


\end_layout

\begin_layout Standard
The first step taken by Lift when evaluating a snippet tag is to resolve
 what snippet method will actually process the content.
 There are several mechanisms that are used to resolve the method, but they
 can be broken down into two main approaches: dispatch via reflection and
 explicit dispatch.
 In addition, Lift allows per-request remapping of snippet names via 
\family typewriter
S.mapSnippet
\family default

\begin_inset Index
status open

\begin_layout Plain Layout
mapSnippet
\end_layout

\end_inset

.
 We'll cover each in the following sections.
\end_layout

\begin_layout Subsection
Implicit Dispatch Via Reflection
\begin_inset Index
status open

\begin_layout Plain Layout
Reflection
\end_layout

\end_inset


\begin_inset Index
status open

\begin_layout Plain Layout
Snippets ! Implicit dispatch
\end_layout

\end_inset


\begin_inset CommandInset label
LatexCommand label
name "sub:Implicit-Dispatch-Via"

\end_inset


\end_layout

\begin_layout Standard
The simplest, and default, approach to resolving snippet names is to use
 implicit dispatch via reflection.
 When using implicit dispatch, Lift will use the snippet name specified
 in the snippet tag to first locate a class.
 Lift will then either instantiate a class, or if it's a stateful snippet
 (we'll cover stateful snippets in Section 
\begin_inset CommandInset ref
LatexCommand ref
reference "sub:Stateless-versus-Stateful"

\end_inset

), retrieve the current instance.
 One Lift has a class instance, it uses the snippet name to further determine
 which method in the class to execute.
 There are three ways to specify this:
\end_layout

\begin_layout Enumerate
Via the 
\family typewriter
type
\family default
 attribute on the snippet tag.
 The value should be 
\begin_inset Quotes eld
\end_inset


\family typewriter
ClassName
\family default
:
\family typewriter
method
\family default

\begin_inset Quotes erd
\end_inset

 for the particular snippet method you want to have handle the tag
\end_layout

\begin_layout Enumerate
Via a tag suffix of 
\family typewriter
Class.method
\family default
.
 This is the same as specifying the 
\family typewriter
type=
\begin_inset Quotes erd
\end_inset

Class:method
\begin_inset Quotes erd
\end_inset


\family default
 attribute
\end_layout

\begin_layout Enumerate
Via a tag suffix of just 
\family typewriter
Class
\family default
.
 This will use the 
\family typewriter
render
\family default
 method on the specified class to handle the tag
\end_layout

\begin_layout Standard
Classes are resolved as specified in Section 
\begin_inset CommandInset ref
LatexCommand ref
reference "sub:Class-Resolution"

\end_inset

.
 
\end_layout

\begin_layout Standard
\align center
\begin_inset Box Shadowbox
position "t"
hor_pos "c"
has_inner_box 1
inner_pos "t"
use_parbox 0
width "75col%"
special "none"
height "1in"
height_special "totalheight"
status open

\begin_layout Plain Layout
The most important thing to remember when using implicit dispatch is that
 your snippet classes must be members of a 
\family typewriter
snippet
\family default
 subpackage as registered by 
\family typewriter
LiftRules.addToPackages
\family default
.
 For example, if you have 
\family typewriter
LiftRules.addToPackages(
\begin_inset Quotes eld
\end_inset

com.foo
\begin_inset Quotes erd
\end_inset

)
\family default
 in your 
\family typewriter
Boot.boot
\family default
 method, snippets should be members of 
\family typewriter
com.foo.snippet
\family default
.
\end_layout

\end_inset


\end_layout

\begin_layout Standard
Listing 
\begin_inset CommandInset ref
LatexCommand ref
reference "lst:Snippet-tag-equivalence"

\end_inset

 shows three equivalent snippet tags.
 Note: these are only equivalent because the method name is 
\begin_inset Quotes eld
\end_inset

render.
\begin_inset Quotes erd
\end_inset

 If we had chosen a different method, e.g., 
\begin_inset Quotes eld
\end_inset

list,
\begin_inset Quotes erd
\end_inset

 then the third example below will still call a 
\begin_inset Quotes eld
\end_inset

render
\begin_inset Quotes erd
\end_inset

 method.
 
\end_layout

\begin_layout Standard
\align center

\family typewriter
\begin_inset Box Shadowbox
position "t"
hor_pos "c"
has_inner_box 1
inner_pos "t"
use_parbox 0
width "75col%"
special "none"
height "1in"
height_special "totalheight"
status open

\begin_layout Plain Layout
It's important to note that with pure implicit dispatch, Java's reflection
 allows access to 
\emph on
any
\emph default
 method on the enclosing class, no matter what the protection on the method
 is set to (e.g.
 private, protected).
 Because of this, it's possible to invoke private and protected methods
 via implicit dispatch, which could be a security concern.This is one reason
 that we recommend using either DispatchSnippet or explicit dispatch for
 production sites.
 We'll cover both of these approaches momentarily.
\end_layout

\begin_layout Plain Layout
Another important note is that lookup via reflection is relatively expensive
\begin_inset Foot
status open

\begin_layout Plain Layout
See 
\begin_inset Flex URL
status collapsed

\begin_layout Plain Layout

http://www.jguru.com/faq/view.jsp?EID=246569
\end_layout

\end_inset

 for a more thorough explanation
\end_layout

\end_inset

 operation, yet another reason that we recommend explicit dispatch for productio
n sites.
\end_layout

\end_inset


\end_layout

\begin_layout Standard
\begin_inset listings
inline false
status open

\begin_layout Plain Layout

\begin_inset Caption

\begin_layout Plain Layout
Snippet Tag Equivalence
\begin_inset CommandInset label
LatexCommand label
name "lst:Snippet-tag-equivalence"

\end_inset


\end_layout

\end_inset


\end_layout

\begin_layout Plain Layout

<lift:snippet type="MyClass:render" />
\end_layout

\begin_layout Plain Layout

<lift:MyClass.render />
\end_layout

\begin_layout Plain Layout

<lift:MyClass />
\end_layout

\end_inset


\end_layout

\begin_layout Standard
In addition to 
\begin_inset Quotes eld
\end_inset

pure
\begin_inset Quotes erd
\end_inset

 implicit dispatch, you can exert a little more control on which method
 in a given class handles a snippet by implementing the 
\family typewriter
net.liftweb.http.DispatchSnippet
\begin_inset Index
status open

\begin_layout Plain Layout
DispatchSnippet
\end_layout

\end_inset


\family default
 trait.
 This trait contains a single method, dispatch, of type 
\begin_inset Formula $PartialFunction[String,NodeSeq\Rightarrow NodeSeq]$
\end_inset

 that maps the method name (the 
\begin_inset Quotes eld
\end_inset

method
\begin_inset Quotes erd
\end_inset

 part of 
\begin_inset Quotes eld
\end_inset

Class.method
\begin_inset Quotes erd
\end_inset

 or 
\begin_inset Quotes eld
\end_inset

Class:method
\begin_inset Quotes erd
\end_inset

 as described above) to a particular method.
 Only method names defined in the dispatch PartialFunction can be executed;
 any methods that aren't covered by the partial function will result in
 a snippet failure.
 Listing 
\begin_inset CommandInset ref
LatexCommand ref
reference "lst:Using-DispatchSnippet-to-select"

\end_inset

 shows how you can control the dispatch by providing a custom 
\family typewriter
dispatch
\family default
 def.
\end_layout

\begin_layout Standard
\begin_inset listings
inline false
status open

\begin_layout Plain Layout

\begin_inset Caption

\begin_layout Plain Layout
Using DispatchSnippet to Control Snippet Method Selection
\begin_inset CommandInset label
LatexCommand label
name "lst:Using-DispatchSnippet-to-select"

\end_inset


\end_layout

\end_inset


\end_layout

\begin_layout Plain Layout

package com.foo.snippet
\end_layout

\begin_layout Plain Layout

\end_layout

\begin_layout Plain Layout

import scala.xml.{NodeSeq,Text}
\end_layout

\begin_layout Plain Layout

import net.liftweb.http.DispatchSnippet
\end_layout

\begin_layout Plain Layout

\end_layout

\begin_layout Plain Layout

class SomeSnippetClass extends DispatchSnippet {
\end_layout

\begin_layout Plain Layout

  def dispatch : DispatchIt = {
\end_layout

\begin_layout Plain Layout

    // We have to use a partially-applied (trailing "_") version
\end_layout

\begin_layout Plain Layout

    // of the functions that we dispatch to
\end_layout

\begin_layout Plain Layout

    case "foo" => myFooMethod _ 
\end_layout

\begin_layout Plain Layout

    case "bar" => someOtherBarMethod _
\end_layout

\begin_layout Plain Layout

    case _ => catchAllMethod _
\end_layout

\begin_layout Plain Layout

  }
\end_layout

\begin_layout Plain Layout

\end_layout

\begin_layout Plain Layout

  def myFooMethod (xhtml : NodeSeq) : NodeSeq = { ...
 }
\end_layout

\begin_layout Plain Layout

  def someOtherBarMethod (xhtml : NodeSeq) : NodeSeq = { ...
 }
\end_layout

\begin_layout Plain Layout

  def catchAllMethod(xhtml : NodeSeq) : NodeSeq = Text("You're being naughty!")
\end_layout

\begin_layout Plain Layout

}
\end_layout

\end_inset


\end_layout

\begin_layout Standard
To summarize, implicit dispatch is the default method by which Lift resolves
 snippet tag names to the actual class and method that will process the
 snippet tag contents.
 Although implicit dispatch is simple to use and works well, security concerns
 lead us to recommend the use of the 
\family typewriter
DispatchSnippet
\begin_inset Index
status open

\begin_layout Plain Layout
DispatchSnippet
\end_layout

\end_inset


\family default
 trait.
 Even with 
\family typewriter
DispatchSnippet
\family default
, however, the implicit class resolution still uses reflection, so if you're
 trying to make things performant you should use explicit dispatch instead.
\end_layout

\begin_layout Subsection
Explicit Dispatch
\begin_inset Index
status open

\begin_layout Plain Layout
Snippets ! Explicit Dispatch
\end_layout

\end_inset


\begin_inset CommandInset label
LatexCommand label
name "sub:Explicit-Dispatch"

\end_inset


\end_layout

\begin_layout Standard
Explicit dispatch allows you to have direct control over which methods will
 be executed for a given snippet name.
 There are two ways that you can define snippet name to method mappings:
 via 
\family typewriter
LiftRules.snippetDispatch
\family default
, which points Lift to 
\family typewriter
DispatchSnippet
\family default
 instances, and 
\family typewriter
LiftRules.snippets
\family default
, which points Lift directly at methods.
\end_layout

\begin_layout Standard
Let's first take a look at 
\family typewriter
LiftRules.snippetDispatch
\family default
, the more generic option.
 When a snippet tag is encountered with a snippet name of the form 
\family typewriter
A.B
\family default
 or 
\family typewriter
A:B
\family default
, Lift will take the first portion (
\family typewriter
A
\family default
) and use that as the lookup for 
\family typewriter
snippetDispatch
\family default
.
 The 
\family typewriter
PartialFunction
\family default
 needs to return an instance of 
\family typewriter
DispatchSnippet
\family default
, so typically you will implement your explicit dispatch snippets using
 an 
\family typewriter
object
\family default
 instead of a 
\family typewriter
class
\family default
.
 Listing 
\begin_inset CommandInset ref
LatexCommand ref
reference "lst:Defining-an-Explicit-snippet"

\end_inset

 shows how we define our object.
 Note that the 
\family typewriter
dispatch
\family default
 method will be executed with the 
\begin_inset Quotes eld
\end_inset


\family typewriter
B
\family default

\begin_inset Quotes erd
\end_inset

 portion of the snippet name (as we defined above) as its argument.
 Other than the fact that it's an object, the definition is essentially
 identical to our implicit dispatch class in Listing 
\begin_inset CommandInset ref
LatexCommand ref
reference "lst:Using-DispatchSnippet-to-select"

\end_inset

.
 
\begin_inset listings
inline false
status open

\begin_layout Plain Layout

\begin_inset Caption

\begin_layout Plain Layout
Defining an Explicit Snippet Object
\begin_inset CommandInset label
LatexCommand label
name "lst:Defining-an-Explicit-snippet"

\end_inset


\end_layout

\end_inset


\end_layout

\begin_layout Plain Layout

// The package *doesn't* need to be "snippet" because there's
\end_layout

\begin_layout Plain Layout

// no reflection involved here
\end_layout

\begin_layout Plain Layout

package com.foo.logic
\end_layout

\begin_layout Plain Layout

\end_layout

\begin_layout Plain Layout

import scala.xml.{NodeSeq,Text}
\end_layout

\begin_layout Plain Layout

import net.liftweb.http.DispatchSnippet
\end_layout

\begin_layout Plain Layout

\end_layout

\begin_layout Plain Layout

object HelloWorld extends DispatchSnippet {
\end_layout

\begin_layout Plain Layout

  // We define dispatch as a val so that it doesn't get re-created
\end_layout

\begin_layout Plain Layout

  // on each request 
\end_layout

\begin_layout Plain Layout

  val dispatch : DispatchIt = {
\end_layout

\begin_layout Plain Layout

    case name => render(name) _
\end_layout

\begin_layout Plain Layout

  }
\end_layout

\begin_layout Plain Layout

\end_layout

\begin_layout Plain Layout

  def render (name : String)(ignore : NodeSeq) : NodeSeq = 
\end_layout

\begin_layout Plain Layout

    Text("Hello, world! Invoked as " + name)
\end_layout

\begin_layout Plain Layout

}
\end_layout

\end_inset


\end_layout

\begin_layout Standard
Now that we have our snippet object, we can bind it to a particular snippet
 name in our 
\family typewriter
Boot.boot
\family default
 method, as shown in Listing 
\begin_inset CommandInset ref
LatexCommand ref
reference "lst:Binding-Our-Explicit-snippet"

\end_inset

.
 It's interesting to note that this is actually how Lift defines many of
 its tags, such as 
\family typewriter
<lift:embed/>
\family default
, 
\family typewriter
<lift:surround/>
\family default
, and 
\family typewriter
<lift:comet/>
\family default
.
 In our case, we've bound our snippet object to 
\family typewriter
<lift:HelloWorld/>
\family default
, and because our 
\family typewriter
DispatchSnippet
\family default
 uses a simple variable binding for its 
\family typewriter
dispatch
\family default
 method case, we can invoke the same snippet with 
\family typewriter
<lift:HelloWorld.hey />
\family default
, 
\family typewriter
<lift:HelloWorld.useless/>
\family default
, or even 
\family typewriter
<lift:HelloWorld.this_is_getting_silly/>
\family default
, and the snippet will tell us what name it was invoked with (
\family typewriter
<lift:HelloWorld/>
\family default
 will invoke with the name 
\begin_inset Quotes eld
\end_inset

render
\begin_inset Quotes erd
\end_inset

, following Lift's normal snippet tag conventions).
 Noe that if you're setting up a dispatch for a 
\family typewriter
StatefulSnippet
\family default

\begin_inset Index
status open

\begin_layout Plain Layout
StatefulSnippet
\end_layout

\end_inset


\begin_inset Index
status open

\begin_layout Plain Layout
Snippets ! stateful
\end_layout

\end_inset

, return a new instance of your 
\family typewriter
StatefulSnippet
\family default
 class.
 
\family typewriter
StatefulSnippet
\family default
 instances will properly register themselves ahead of the 
\family typewriter
snippetDispatch
\family default
 partial function on each successive request.
\end_layout

\begin_layout Standard
\begin_inset listings
inline false
status open

\begin_layout Plain Layout

\begin_inset Caption

\begin_layout Plain Layout
Binding Our Explicit Snippet Object
\begin_inset CommandInset label
LatexCommand label
name "lst:Binding-Our-Explicit-snippet"

\end_inset


\end_layout

\end_inset


\end_layout

\begin_layout Plain Layout

class Boot {
\end_layout

\begin_layout Plain Layout

  def boot {
\end_layout

\begin_layout Plain Layout

    ...
\end_layout

\begin_layout Plain Layout

    LiftRules.snippetDispatch.append {
\end_layout

\begin_layout Plain Layout

      case "HelloWorld" => com.foo.logic.HelloWorld
\end_layout

\begin_layout Plain Layout

      // For StatefulSnippets, return a *new instance*
\end_layout

\begin_layout Plain Layout

      case "HelloConversation" => 
\end_layout

\begin_layout Plain Layout

        new com.foo.logic.StatefulHelloWorld
\end_layout

\begin_layout Plain Layout

    }
\end_layout

\begin_layout Plain Layout

  }
\end_layout

\begin_layout Plain Layout

}
\end_layout

\end_inset


\end_layout

\begin_layout Standard
Now let's look at 
\family typewriter
LiftRules.snippets
\family default
.
 This is a more fine-grained approach to explicit dispatch that doesn't
 require the 
\family typewriter
DispatchSnippet
\family default
 trait.
 Instead, we bind a list of snippet name components corresponding to the
 parts of the snippet name separated by either 
\begin_inset Quotes eld
\end_inset

:
\begin_inset Quotes erd
\end_inset

 or 
\begin_inset Quotes eld
\end_inset

.
\begin_inset Quotes erd
\end_inset

, and point it directly at a given snippet method.
 Assuming we're using the same snippet object in Listing 
\begin_inset CommandInset ref
LatexCommand ref
reference "lst:Defining-an-Explicit-snippet"

\end_inset

, we can bind the 
\family typewriter
<lift:HelloWorld/>
\family default
 tag by setting up 
\family typewriter
LiftRules.snippets
\family default
 in our Boot.boot method as shown in Listing 
\begin_inset CommandInset ref
LatexCommand ref
reference "lst:Explicitly-Binding-a-snippet"

\end_inset

.
 Notice that in order to bind the same way that we did with 
\family typewriter
snippetDispatch
\family default
, we need two lines to match the un-suffixed and suffixed versions.
 If you omit the un-suffixed line you will get a snippet failure.
 
\begin_inset listings
inline false
status open

\begin_layout Plain Layout

\begin_inset Caption

\begin_layout Plain Layout
Explicitly Binding a Snippet Method
\begin_inset CommandInset label
LatexCommand label
name "lst:Explicitly-Binding-a-snippet"

\end_inset


\end_layout

\end_inset


\end_layout

\begin_layout Plain Layout

import com.foo.logic
\end_layout

\begin_layout Plain Layout

class Boot {
\end_layout

\begin_layout Plain Layout

  def boot {
\end_layout

\begin_layout Plain Layout

    ...
\end_layout

\begin_layout Plain Layout

    LiftRules.snippets.append {
\end_layout

\begin_layout Plain Layout

      // Matches a tag without a suffix (<lift:HelloWorld />)
\end_layout

\begin_layout Plain Layout

      case List("HelloWorld") => HelloWorld.render("no name") _
\end_layout

\begin_layout Plain Layout

      case List("HelloWorld", name) => HelloWorld.render(name) _
\end_layout

\begin_layout Plain Layout

    }
\end_layout

\begin_layout Plain Layout

  }
\end_layout

\begin_layout Plain Layout

}
\end_layout

\end_inset


\end_layout

\begin_layout Subsection
Per-request Remapping
\begin_inset Index
status open

\begin_layout Plain Layout
Snippets ! Per-request remapping
\end_layout

\end_inset


\end_layout

\begin_layout Standard
The final piece of snippet mapping that we want to discuss is per-request
 remapping.
 The S.mapSnippet method allows you to modify which snippet method will service
 a given snippet tag within your page processing.
 For example, Listing 
\begin_inset CommandInset ref
LatexCommand ref
reference "lst:Remapping-A-Snippet"

\end_inset

 shows how we can conditionally 
\begin_inset Quotes eld
\end_inset

blank
\begin_inset Quotes erd
\end_inset

 a snippet based on logic in a second snippet.
 This functionality isn't used frequently as the other types of snippet
 dispatch, but it's here in case you need it.
\end_layout

\begin_layout Standard
\begin_inset listings
inline false
status open

\begin_layout Plain Layout

\begin_inset Caption

\begin_layout Plain Layout
Remapping A Snippet
\begin_inset CommandInset label
LatexCommand label
name "lst:Remapping-A-Snippet"

\end_inset


\end_layout

\end_inset


\end_layout

\begin_layout Plain Layout

import scala.xml.NodeSeq
\end_layout

\begin_layout Plain Layout

import net.liftweb.http.S
\end_layout

\begin_layout Plain Layout

\end_layout

\begin_layout Plain Layout

class Display {
\end_layout

\begin_layout Plain Layout

  def header (xhtml : NodeSeq) : NodeSeq = {
\end_layout

\begin_layout Plain Layout

    ...
\end_layout

\begin_layout Plain Layout

    // If simple is set, we don't display complexStuff
\end_layout

\begin_layout Plain Layout

    S.param("simple").foreach {
\end_layout

\begin_layout Plain Layout

      S.mapSnippet("complexStuff", ignore => Text(""))
\end_layout

\begin_layout Plain Layout

    }
\end_layout

\begin_layout Plain Layout

  }
\end_layout

\begin_layout Plain Layout

\end_layout

\begin_layout Plain Layout

  def complexStuff (xhtml : NodeSeq) : NodeSeq = {
\end_layout

\begin_layout Plain Layout

    ...
\end_layout

\begin_layout Plain Layout

  }
\end_layout

\begin_layout Plain Layout

}
\end_layout

\end_inset


\end_layout

\begin_layout Section
Snippet Methods
\begin_inset CommandInset label
LatexCommand label
name "sec:Snippets"

\end_inset


\begin_inset Note Note
status open

\begin_layout Plain Layout
Must revise from here down
\end_layout

\end_inset


\end_layout

\begin_layout Standard
Now that we've examined how Lift determines which snippet to execute, let's
 look at what a snippet method actually does.
 A snippet method is essentially a transform, taking a single 
\family typewriter
scala.xml.NodeSeq
\family default

\begin_inset Index
status collapsed

\begin_layout Plain Layout
NodeSeq
\end_layout

\end_inset

 argument and returning a 
\family typewriter
NodeSeq
\family default
.
\end_layout

\begin_layout Standard
\align center
\begin_inset Box Shadowbox
position "t"
hor_pos "c"
has_inner_box 1
inner_pos "t"
use_parbox 0
width "75col%"
special "none"
height "1in"
height_special "totalheight"
status open

\begin_layout Plain Layout
Note: Although Scala can often infer return types, it's important to explicitly
 specify the return type of your snippet methods as 
\family typewriter
NodeSeq
\family default
.
 Failure to do so may prevent Lift from locating the snippet method if you're
 using implicit dispatch (Section 
\begin_inset CommandInset ref
LatexCommand ref
reference "sub:Implicit-Dispatch-Via"

\end_inset

), in which case the snippet won't execute!
\end_layout

\end_inset


\end_layout

\begin_layout Standard
The argument passed to the snippet method is the XML content of the snippet
 tag.
 Because Lift processes XML from the root element down to the child elements
 (outside-in), the contents of the snippet tag aren't processed until 
\emph on
after
\emph default
 the snippet method processes them.
 You may reverse the order of processing by specifying the 
\family typewriter
eager_eval
\family default
 attribute on the tag (Section 
\begin_inset CommandInset ref
LatexCommand ref
reference "sub:Eager-Eval"

\end_inset

).
 As an example, let's say we wanted a snippet that would output the current
 balance of our ledger, shown in Listing 
\begin_inset CommandInset ref
LatexCommand ref
reference "lst:Returning-tags-snippet"

\end_inset

.
 We simply return an XML Text node with the formatted balance.
 Note that the XML result from a snippet is itself processed recursively,
 so the 
\family typewriter
lift:Util.time
\family default
 snippet will be processed after our snippet method returns.
\end_layout

\begin_layout Standard
\begin_inset listings
inline false
status open

\begin_layout Plain Layout

\begin_inset Caption

\begin_layout Plain Layout
Returning Tags from a Snippet
\begin_inset CommandInset label
LatexCommand label
name "lst:Returning-tags-snippet"

\end_inset


\end_layout

\end_inset


\end_layout

\begin_layout Plain Layout

class Ledger {
\end_layout

\begin_layout Plain Layout

  def balance (content : NodeSeq) : NodeSeq = 
\end_layout

\begin_layout Plain Layout

    <p>{currentLedger.formattedBalance}
\end_layout

\begin_layout Plain Layout

      as of <lift:Util.time /></p>
\end_layout

\begin_layout Plain Layout

}
\end_layout

\end_inset


\end_layout

\begin_layout Standard
It is this hierarchical processing of template tags that makes Lift so flexible.
 For those of you coming to Lift with some JSP experience, Lift is designed
 to let you write something similar to tag libraries, but that are much
 more powerful and much simpler to use.
\end_layout

\begin_layout Subsection
Binding Values in Snippets
\begin_inset CommandInset label
LatexCommand label
name "sub:Binding-Values-in-snippets"

\end_inset


\begin_inset Index
status open

\begin_layout Plain Layout
Binding
\end_layout

\end_inset


\begin_inset Index
status open

\begin_layout Plain Layout
Snippets ! binding
\end_layout

\end_inset


\end_layout

\begin_layout Standard
So far we've shown our snippets generating complete output and ignoring
 the input to the method.
 Lift actually provides some very nice facilities for using the input 
\family typewriter
NodeSeq
\family default
 within your snippet to help keep presentation and code separate.
 First, remember that the input 
\family typewriter
NodeSeq
\family default
 consists of the child elements for the snippet tag in your template.
\end_layout

\begin_layout Standard
\begin_inset listings
inline false
status open

\begin_layout Plain Layout

\begin_inset Caption

\begin_layout Plain Layout
Snippet Tag Children
\begin_inset CommandInset label
LatexCommand label
name "lst:Snippet-tag-children"

\end_inset


\end_layout

\end_inset


\end_layout

\begin_layout Plain Layout

<lift:Ledger.balance>
\end_layout

\begin_layout Plain Layout

  <ledger:balance/> as of <ledger:time />
\end_layout

\begin_layout Plain Layout

</lift:Ledger.balance>
\end_layout

\end_inset


\end_layout

\begin_layout Standard
For example, given a template containing the snippet tag shown in Listing
 
\begin_inset CommandInset ref
LatexCommand ref
reference "lst:Snippet-tag-children"

\end_inset

, the Ledger.balance method receives
\end_layout

\begin_layout LyX-Code
<ledger:balance/> as of <ledger:time />
\end_layout

\begin_layout Standard
as its input parameter.
 This is perfectly correct XML, although it may look a little strange at
 first unless you've used prefixed elements in XML before.
 The key is that Lift allows you to selectively 
\begin_inset Quotes eld
\end_inset

bind
\begin_inset Quotes erd
\end_inset

, or replace, these elements with data inside your snippet.
 The 
\family typewriter
Helpers.bind
\family default

\begin_inset Foot
status open

\begin_layout Plain Layout
net.liftweb.util.Helpers.
 Technically the bind method is overloaded, and can even fill in values
 for the lift:bind tag, but this is advanced usage and we're not going to
 cover that here.
\end_layout

\end_inset

 method takes three arguments:
\end_layout

\begin_layout Enumerate
The prefix for the tags you wish to bind, in this instance, 
\begin_inset Quotes eld
\end_inset

ledger
\begin_inset Quotes erd
\end_inset


\end_layout

\begin_layout Enumerate
The 
\family typewriter
NodeSeq
\family default
 that contains the tags you wish to bind
\end_layout

\begin_layout Enumerate
One or more 
\family typewriter
BindParam
\family default
 elements that map the tag name to a replacement value
\end_layout

\begin_layout Standard
While you can create your own 
\family typewriter
BindParam
\family default
 instances by hand, we generally recommend importing 
\family typewriter
Helpers._
\family default
, which among other things contains a convenient implicit conversion to
 BindParam using the 
\begin_inset Quotes eld
\end_inset

->
\begin_inset Quotes erd
\end_inset

 operator.
 With this knowledge in hand, we can change our previous definition of the
 balance method in Listing 
\begin_inset CommandInset ref
LatexCommand ref
reference "lst:Returning-tags-snippet"

\end_inset

 to that in Listing 
\begin_inset CommandInset ref
LatexCommand ref
reference "lst:Binding-the-ledger-balance"

\end_inset

 below.
\end_layout

\begin_layout Standard
\begin_inset listings
inline false
status open

\begin_layout Plain Layout

\begin_inset Caption

\begin_layout Plain Layout
Binding the Ledger Balance
\begin_inset CommandInset label
LatexCommand label
name "lst:Binding-the-ledger-balance"

\end_inset


\end_layout

\end_inset


\end_layout

\begin_layout Plain Layout

class Ledger {
\end_layout

\begin_layout Plain Layout

  def balance (content : NodeSeq ) : NodeSeq = 
\end_layout

\begin_layout Plain Layout

    bind ("ledger", content,
\end_layout

\begin_layout Plain Layout

          "balance" -> Text(currentLedger.formattedBalance),
\end_layout

\begin_layout Plain Layout

          "time" -> Text((new java.util.Date).toString))
\end_layout

\begin_layout Plain Layout

}
\end_layout

\end_inset


\end_layout

\begin_layout Standard
As you can see here, we actually gain a line of code over our previous effort,
 but the trade-off makes it far simpler for us to change the layout just
 by editing the template.
\end_layout

\begin_layout Standard
One last aspect of binding that we want to discuss is that any attributes
 set on the input elements that are being bound will be discarded
\begin_inset Index
status open

\begin_layout Plain Layout
Attributes ! discarded in bind
\end_layout

\end_inset

 if you use the 
\begin_inset Quotes eld
\end_inset

->
\begin_inset Quotes erd
\end_inset

 binding operator.
 See Section 
\begin_inset CommandInset ref
LatexCommand ref
reference "sec:Handling-XHTML-Attributes"

\end_inset

 for more details on how you manipulate attributes in bindings, including
 how you can retain attributes on binding elements from your templates by
 using the 
\begin_inset Quotes eld
\end_inset

-%>
\begin_inset Quotes erd
\end_inset


\begin_inset Index
status open

\begin_layout Plain Layout
Attributes ! -%> operator
\end_layout

\end_inset

 binding operator instead.
\end_layout

\begin_layout Subsection
CSS Selector Transforms
\begin_inset CommandInset label
LatexCommand label
name "sub:CSS-Selector-Transforms"

\end_inset


\begin_inset Index
status open

\begin_layout Plain Layout
CSS ! selector transforms
\end_layout

\end_inset


\begin_inset Index
status open

\begin_layout Plain Layout
Binding ! with CSS
\end_layout

\end_inset


\begin_inset Index
status open

\begin_layout Plain Layout
Snippets ! binding with CSS
\end_layout

\end_inset


\begin_inset Index
status open

\begin_layout Plain Layout
CSS Transforms
\end_layout

\end_inset


\end_layout

\begin_layout Standard
In addition to the binding support detailed in Section 
\begin_inset CommandInset ref
LatexCommand ref
reference "sub:Binding-Values-in-snippets"

\end_inset

, Lift 2.2 introduces binding via CSS transforms as part of its support for
 designer friendly templates.
 These allow you to bind values into template XHTML (or HTML5, see Section
 
\begin_inset CommandInset ref
LatexCommand vref
reference "sec:HTML5-Support"

\end_inset

) by using the attributes on specific elements.
 Let's start by looking at a basic example, corresponding to the examples
 in Section 
\begin_inset CommandInset ref
LatexCommand ref
reference "sub:Binding-Values-in-snippets"

\end_inset

.
\end_layout

\begin_layout Standard
Listing 
\begin_inset CommandInset ref
LatexCommand ref
reference "lst:A-Simple-CSS-snippet"

\end_inset

 shows a Designer-Friendly version of Listing 
\begin_inset CommandInset ref
LatexCommand ref
reference "lst:Snippet-tag-children"

\end_inset

.
 You can see that we're invoking the 
\family typewriter
Ledger.balance
\family default
 snippet via the class attribute, and we've specified the binding elements
 as normal 
\family typewriter
<span/>
\family default
 elements with 
\family typewriter
id
\family default
 attributes.
\end_layout

\begin_layout Standard
\begin_inset listings
inline false
status open

\begin_layout Plain Layout

\begin_inset Caption

\begin_layout Plain Layout

A Simple CSS Snippet
\begin_inset CommandInset label
LatexCommand label
name "lst:A-Simple-CSS-snippet"

\end_inset


\end_layout

\end_inset


\end_layout

\begin_layout Plain Layout

<div class="lift:Ledger.balance">
\end_layout

\begin_layout Plain Layout

  <span id="balance">$0</span> as of <span id="time">midnight</span>
\end_layout

\begin_layout Plain Layout

</div>
\end_layout

\end_inset


\end_layout

\begin_layout Standard
Now, we need to perform the CSS transform within our snippet.
 The binding implicits for CSS transforms are found on the 
\family typewriter
net.liftweb.util.BindHelpers
\family default
 object/trait, so you should import it (in particular, the 
\family typewriter
strToCssBindPromoter
\family default
 method).
 Listing 
\begin_inset CommandInset ref
LatexCommand ref
reference "lst:Binding-the-Ledger-with-CSS"

\end_inset

 shows how we modify the snippet in Listing 
\begin_inset CommandInset ref
LatexCommand ref
reference "lst:Binding-the-ledger-balance"

\end_inset

 to utilize the new CSS transform.
\end_layout

\begin_layout Standard
\begin_inset listings
inline false
status open

\begin_layout Plain Layout

\begin_inset Caption

\begin_layout Plain Layout

Binding the Ledger Balance with CSS
\begin_inset CommandInset label
LatexCommand label
name "lst:Binding-the-Ledger-with-CSS"

\end_inset


\end_layout

\end_inset


\end_layout

\begin_layout Plain Layout

import net.liftweb.util.BindHelpers._
\end_layout

\begin_layout Plain Layout

\end_layout

\begin_layout Plain Layout

class Ledger {
\end_layout

\begin_layout Plain Layout

  def balance = "#balance" #> currentLedger.formattedBalance &
\end_layout

\begin_layout Plain Layout

    "#time" #> (new java.util.Date).toString
\end_layout

\begin_layout Plain Layout

}
\end_layout

\end_inset


\end_layout

\begin_layout Standard
As you can see in this example, CSS transforms are comprised of three parts:
 the transform selector, the transform operator (
\family typewriter
#>
\family default
), and the right hand side value.
 This value can be a number of different things, which we'll cover in Section
 
\begin_inset CommandInset ref
LatexCommand ref
reference "sub:Replacement-Values"

\end_inset

, but in our case we're using a 
\family typewriter
MappedField
\family default
 and a 
\family typewriter
String
\family default
.
 Additionally, you can chain transforms together with the 
\family typewriter
&
\family default
 operator.
\end_layout

\begin_layout Subsubsection
CSS Selector Syntax
\end_layout

\begin_layout Standard
The selector syntax is based on a subset of CSS, so if you already know
 that you're well on your way.
 The syntax can operate on elements based on id or class, and can also operate
 on attributes of those elements.
 Let's look at the basic syntax:
\end_layout

\begin_layout Itemize

\family typewriter
#foo
\family default
 - Selects the element with an id attribute of 
\begin_inset Quotes eld
\end_inset

foo
\begin_inset Quotes erd
\end_inset


\end_layout

\begin_layout Itemize

\family typewriter
.foo
\family default
 - Selects all elements with class of 
\begin_inset Quotes eld
\end_inset

foo
\begin_inset Quotes erd
\end_inset


\end_layout

\begin_layout Itemize

\family typewriter
attrName=attrValue
\family default
 - Selects all elements with an attribute of 
\begin_inset Quotes eld
\end_inset

attrName
\begin_inset Quotes erd
\end_inset

 equal to 
\begin_inset Quotes eld
\end_inset

attrValue
\begin_inset Quotes erd
\end_inset


\end_layout

\begin_layout Itemize

\family typewriter
element
\family default
 - Selects all 
\begin_inset Quotes eld
\end_inset

element
\begin_inset Quotes erd
\end_inset

 elements (e.g.
 span, h1, etc.)
\end_layout

\begin_layout Itemize

\family typewriter
*
\family default
 - Selects all elements
\end_layout

\begin_layout Standard
The element matching the selector is replaced by the result of processing
 the replacement.
 That means that in the example of Listing 
\begin_inset CommandInset ref
LatexCommand ref
reference "lst:A-Simple-CSS-snippet"

\end_inset

 the 
\family typewriter
span
\family default
 elements will be replaced with straight Text elements, resulting in the
 markup shown in Listing 
\begin_inset CommandInset ref
LatexCommand ref
reference "lst:Sample-CSS-Transform-result"

\end_inset

 (in other words, no remaining markup).
\end_layout

\begin_layout Standard
\begin_inset listings
lstparams "language=XML"
inline false
status open

\begin_layout Plain Layout

\begin_inset Caption

\begin_layout Plain Layout

Sample CSS Transform Result
\begin_inset CommandInset label
LatexCommand label
name "lst:Sample-CSS-Transform-result"

\end_inset


\end_layout

\end_inset


\end_layout

\begin_layout Plain Layout

$12.42 as of Fri Jan 14 08:29:50 MST 2011
\end_layout

\end_inset


\end_layout

\begin_layout Standard
You can further refine the replacement with an optional qualifier.
 We've already seen how omitting the qualifer results in wholesale replacement
 of the matching element, but there are a few additional options:
\end_layout

\begin_layout Itemize

\family typewriter
*
\family default
 - Replaces the children of the selected element.
 For example, if we changed our selector in Listing 
\begin_inset CommandInset ref
LatexCommand ref
reference "lst:Binding-the-Ledger-with-CSS"

\end_inset

 from 
\family typewriter

\begin_inset Quotes eld
\end_inset

#balance
\begin_inset Quotes erd
\end_inset


\family default
 to 
\family typewriter

\begin_inset Quotes eld
\end_inset

#balance *
\begin_inset Quotes erd
\end_inset


\family default
, we would be replacing the text node child (
\begin_inset Quotes eld
\end_inset

$0
\begin_inset Quotes erd
\end_inset

), with the resulting markup:
\end_layout

\begin_deeper
\begin_layout Standard
\begin_inset listings
lstparams "frame=none,language=HTML"
inline false
status open

\begin_layout Plain Layout

<span id="balance">$12.42</span> as of Fri Jan 14 08:29:50 MST 2011
\end_layout

\end_inset


\end_layout

\begin_layout Standard
Note that when we perform child replacement, the parent's attributes
\begin_inset Index
status open

\begin_layout Plain Layout
CSS Transforms ! attribute copying
\end_layout

\end_inset

 are carried over to the resulting element.
 There is an exception to this in the case of iterated replacements, which
 we'll cover in Section 
\begin_inset CommandInset ref
LatexCommand ref
reference "sub:Replacement-Values"

\end_inset

.
\end_layout

\end_deeper
\begin_layout Itemize

\family typewriter
[name]
\family default
 - 
\begin_inset Index
status open

\begin_layout Plain Layout
CSS Transforms ! attribute replacement
\end_layout

\end_inset

Sets the value of the 
\family typewriter

\begin_inset Quotes erd
\end_inset

name
\begin_inset Quotes erd
\end_inset


\family default
 attribute on the selected element.
 If the attribute already exists on the selected element, its value is replaced,
 otherwise the attribute is added.
 For example, if we wanted to replace both the link text and 
\family typewriter
href
\family default
 of a link via CSS transform for the template
\end_layout

\begin_deeper
\begin_layout Standard
\begin_inset listings
lstparams "frame=none,language=HTML"
inline false
status open

\begin_layout Plain Layout

<a href="#">ReplaceMe</a>
\end_layout

\end_inset


\end_layout

\begin_layout Standard
We could perform this by chaining two selections together, one for the child
 element (link text) and one for the 
\family typewriter
href
\family default
 attribute:
\end_layout

\begin_layout Standard
\begin_inset listings
lstparams "frame=none"
inline false
status open

\begin_layout Plain Layout

"a *" #> "This is the link text"& "a [href]" #> "http://foo.com/bar"
\end_layout

\end_inset


\end_layout

\begin_layout Standard
Note that the order of the selections is not important.
\end_layout

\end_deeper
\begin_layout Itemize

\family typewriter
[name+]
\family default
 - Appends a value to the attribute on the selected element.
 If the attribute doesn't already exist on the element then this behaves
 the same as the 
\family typewriter
[name]
\family default
 qualifier.
 One example would be adding to the 
\family typewriter
class
\family default
 attribute for a given element:
\end_layout

\begin_deeper
\begin_layout Standard
\begin_inset listings
lstparams "frame=none"
inline false
status open

\begin_layout Plain Layout

"tr [class+]" #> (if (index % 2) "odd" else "even")
\end_layout

\end_inset


\end_layout

\end_deeper
\begin_layout Itemize

\family typewriter
^^
\family default
 - Makes the selected element the root of the returned elements.
 This can be used to select a particular element from a template, similar
 to 
\family typewriter
BindHelpers.chooseTemplate
\family default
.
 The right hand side for the selected element is ignored, but you can chain
 further transforms to modify the returned element.
 For example, if we decided to only output the balance in Listing 
\begin_inset CommandInset ref
LatexCommand ref
reference "lst:A-Simple-CSS-snippet"

\end_inset

, we could do so by changing our snippet code to:
\end_layout

\begin_deeper
\begin_layout Standard
\begin_inset listings
lstparams "frame=none"
inline false
status open

\begin_layout Plain Layout

def balance = "#balance ^^" #> "ignore" &
\end_layout

\begin_layout Plain Layout

  "#balance" #> currentLedger.formattedBalance
\end_layout

\end_inset


\end_layout

\end_deeper
\begin_layout Subsubsection
Right Hand Side Values
\begin_inset CommandInset label
LatexCommand label
name "sub:Replacement-Values"

\end_inset


\end_layout

\begin_layout Standard
The right hand side of a CSS transform operates on the selected element
 to either transform or replace it.
 It can be one of:
\end_layout

\begin_layout Itemize

\family typewriter
String
\family default
 constant - returns a Text node for the 
\family typewriter
String
\family default
.
 For example, in Listing 
\begin_inset CommandInset ref
LatexCommand ref
reference "lst:Binding-the-Ledger-with-CSS"

\end_inset

:
\end_layout

\begin_deeper
\begin_layout Standard
\begin_inset listings
lstparams "frame=none"
inline false
status open

\begin_layout Plain Layout

"#time" #> (new java.util.Date).toString
\end_layout

\end_inset


\end_layout

\end_deeper
\begin_layout Itemize
A 
\family typewriter
NodeSeq
\family default
 constant - returns the 
\family typewriter
NodeSeq
\family default
 itself.
 In Listing 
\begin_inset CommandInset ref
LatexCommand ref
reference "lst:Binding-the-Ledger-with-CSS"

\end_inset

 we could have done this instead:
\end_layout

\begin_deeper
\begin_layout Standard
\begin_inset listings
lstparams "frame=none"
inline false
status open

\begin_layout Plain Layout

"#time" #> Text((new java.util.Date).toString)
\end_layout

\end_inset


\end_layout

\end_deeper
\begin_layout Itemize
\begin_inset Formula $NodeSeq\Rightarrow NodeSeq$
\end_inset

 - a function that transforms the selected element.
 Note that CSS transforms extend 
\begin_inset Formula $NodeSeq\Rightarrow NodeSeq$
\end_inset

, so you can nest transforms like
\end_layout

\begin_deeper
\begin_layout Standard
\begin_inset listings
lstparams "frame=none"
inline false
status open

\begin_layout Plain Layout

// Select the element with id "entry" and then bind its 
\end_layout

\begin_layout Plain Layout

// nested "name" element
\end_layout

\begin_layout Plain Layout

"#entry" #> { "#name" #> account.name }
\end_layout

\end_inset


\end_layout

\end_deeper
\begin_layout Itemize

\family typewriter
net.liftweb.util.Bindable
\family default
 - Instances that implement the 
\family typewriter
Bindable
\family default
 trait will be automatically converted into a 
\family typewriter
NodeSeq
\family default
.
 Among other things, 
\family typewriter
MappedField
\family default
 and 
\family typewriter
Record.Field
\family default
 support this, which allows us to use instances directly:
\end_layout

\begin_deeper
\begin_layout Standard
\begin_inset listings
lstparams "frame=none"
inline false
status open

\begin_layout Plain Layout

"#description" #> account.description
\end_layout

\end_inset


\end_layout

\end_deeper
\begin_layout Itemize

\family typewriter
Boolean
\family default
, 
\family typewriter
Int
\family default
, 
\family typewriter
Long
\family default
 or 
\family typewriter
Symbol
\family default
 - These are automatically promoted to a 
\family typewriter
String
\family default
 via the 
\family typewriter
net.liftweb.util.StringPromotable
\family default
 trait and implicits on its companion object
\end_layout

\begin_deeper
\begin_layout Standard
\begin_inset listings
lstparams "frame=none"
inline false
status open

\begin_layout Plain Layout

"#viewperm" #> account.isViewableBy(someUser)
\end_layout

\end_inset


\end_layout

\end_deeper
\begin_layout Itemize
A 
\family typewriter
Box
\family default
, 
\family typewriter
Option
\family default
 or 
\family typewriter
Seq
\family default
 of 
\family typewriter
String
\family default
, 
\family typewriter
NodeSeq
\family default
, 
\family typewriter
Bindable
\family default
 or values convertable by 
\family typewriter
StringPromotable
\family default
 - These will be converted into a 
\family typewriter
net.liftweb.util.IterableConst
\family default
, which is used to compute a 
\family typewriter
Seq[NodeSeq]
\family default
.
 If your selector replaces the children of the selected element (*), the
 
\family typewriter
IterableConst
\family default
 is applied to the selected element once for each item in the 
\family typewriter
Seq
\family default
.
 In other words, you get a copy of the selected element for each original
 input.
 For example, given the template:
\end_layout

\begin_deeper
\begin_layout Standard
\begin_inset listings
lstparams "frame=none,language=HTML"
inline false
status open

\begin_layout Plain Layout

<h2>Account names:</h2>
\end_layout

\begin_layout Plain Layout

<ul>
\end_layout

\begin_layout Plain Layout

  <li id="item">Account</li>
\end_layout

\begin_layout Plain Layout

</ul>
\end_layout

\end_inset


\end_layout

\begin_layout Standard
We can iterate over a list of accounts with the CSS transform:
\end_layout

\begin_layout Standard
\begin_inset listings
lstparams "frame=none"
inline false
status open

\begin_layout Plain Layout

"#item *" #> accounts.map(_.name.toString)
\end_layout

\end_inset


\end_layout

\begin_layout Standard
Which, assuming a set of accounts named 
\begin_inset Quotes eld
\end_inset

A
\begin_inset Quotes erd
\end_inset

, 
\begin_inset Quotes eld
\end_inset

B
\begin_inset Quotes erd
\end_inset

, and 
\begin_inset Quotes eld
\end_inset

C
\begin_inset Quotes erd
\end_inset

, results in:
\end_layout

\begin_layout Standard
\begin_inset listings
lstparams "frame=none,language=HTML"
inline false
status open

\begin_layout Plain Layout

<h2>Account names:</h2>
\end_layout

\begin_layout Plain Layout

<ul>
\end_layout

\begin_layout Plain Layout

  <li id="item">A</li>
\end_layout

\begin_layout Plain Layout

  <li>B</li>
\end_layout

\begin_layout Plain Layout

  <li>C</li>
\end_layout

\begin_layout Plain Layout

</ul>
\end_layout

\end_inset


\end_layout

\begin_layout Standard
\begin_inset Box Shadowbox
position "t"
hor_pos "c"
has_inner_box 1
inner_pos "t"
use_parbox 0
width "80col%"
special "none"
height "1in"
height_special "totalheight"
status open

\begin_layout Plain Layout
Note that the 
\family typewriter
id
\family default
 attribute is only placed on the first transformed element.
 Subsequent replacements strip the 
\family typewriter
id
\family default
 attribute so that it remains unique on the page.
 This special handling applies only to the 
\family typewriter
id
\family default
 attribute; other attributes, such as 
\family typewriter
class
\family default
, are not similarly stripped.
\end_layout

\end_inset


\end_layout

\end_deeper
\begin_layout Itemize
A 
\family typewriter
Box
\family default
, 
\family typewriter
Option
\family default
 or 
\family typewriter
Seq
\family default
 of 
\begin_inset Formula $NodeSeq\Rightarrow NodeSeq$
\end_inset

 - These will be converted into a 
\family typewriter
net.liftweb.util.IterableFunc
\family default
, and follow the same rules for replacement as 
\family typewriter
IterableConst
\family default
 (e.g.
 child replacement repetition).
\end_layout

\begin_layout Subsection
Stateless versus Stateful Snippets
\begin_inset CommandInset label
LatexCommand label
name "sub:Stateless-versus-Stateful"

\end_inset


\begin_inset Index
status open

\begin_layout Plain Layout
StatefulSnippet
\end_layout

\end_inset


\begin_inset Index
status open

\begin_layout Plain Layout
Snippets ! stateful vs stateless
\end_layout

\end_inset


\end_layout

\begin_layout Standard
The lifecycle of a snippet is stateless by default.
 That means that for each request, Lift creates a new instance of the snippet
 class to execute (or uses the same staic method if using explicit dispatch,
 Section 
\begin_inset CommandInset ref
LatexCommand ref
reference "sub:Explicit-Dispatch"

\end_inset

).
 Any changes you make to instance variables will be discarded after the
 request is processed.
 If you want to keep some state around, you have a couple of options:
\end_layout

\begin_layout Itemize
Store the state in a cookie
\begin_inset Index
status open

\begin_layout Plain Layout
cookie
\end_layout

\end_inset

 (Section 
\begin_inset CommandInset ref
LatexCommand ref
reference "sec:Cookies"

\end_inset

).
 This can be useful if you have data that you want to persist across sessions.
 The down side is that you have to manage the cookie as well as deal with
 any security implications for the data in the cookie as it's stored on
 the user's machine.
\end_layout

\begin_layout Itemize
Store the state in a 
\family typewriter
SessionVar
\family default

\begin_inset Index
status open

\begin_layout Plain Layout
SessionVar
\end_layout

\end_inset

 (Section 
\begin_inset CommandInset ref
LatexCommand ref
reference "sec:Session-and-Request"

\end_inset

).
 This is a little easier to manage than cookies, but you still have to handle
 adding and removing the session data if you don't want it around for the
 duration of the session.
 As with a cookie, it is global, which means that it will be the same for
 all snippet instances for a given session.
\end_layout

\begin_layout Itemize
Pass the state around in a 
\family typewriter
RequestVar
\family default

\begin_inset Index
status open

\begin_layout Plain Layout
RequestVar
\end_layout

\end_inset

 by setting 
\begin_inset Quotes eld
\end_inset

injector
\begin_inset Quotes erd
\end_inset

 functions in your page transition functions (e.g.
 
\family typewriter
SHtml.link
\family default
, 
\family typewriter
S.redirectTo
\family default
, etc).
 We cover this technique in Section 
\begin_inset CommandInset ref
LatexCommand ref
reference "sec:Session-and-Request"

\end_inset

.
\end_layout

\begin_layout Itemize
Use a 
\family typewriter
StatefulSnippet
\family default

\begin_inset Index
status open

\begin_layout Plain Layout
StatefulSnippet
\end_layout

\end_inset

 subclass.
 This is ideal for small, conversational state, such as a form that spans
 multiple pages or for a page where you have multiple variables that you
 want to be able to tweak individually.
\end_layout

\begin_layout Standard
Using a 
\family typewriter
StatefulSnippet
\family default
 is very similar to using a normal snippet but with the addition of a few
 mechanisms.
 First, the 
\family typewriter
State
\family default
fulSnippet trait extends 
\family typewriter
DispatchSnippet
\family default
 (see Section 
\begin_inset CommandInset ref
LatexCommand ref
reference "sub:Implicit-Dispatch-Via"

\end_inset

), allowing you to define which methods handle which snippets based on the
 
\family typewriter
dispatch
\family default
 method.
 Because Scala allows 
\family typewriter
def
\family default
s to be implemented by 
\family typewriter
var
\family default
s in subclasses, we can redefine the dispatch behavior as a result of snippet
 processing.
 
\end_layout

\begin_layout Standard
Another thing to remember when using 
\family typewriter
StatefulSnippet
\family default
s is that when you render a form, a hidden field is added to the form that
 permits the same instance of the 
\family typewriter
StatefulSnippet
\family default
 that created the form to be the target of the form submission.
 If you need to link to a different page, but would like the same snippet
 instance to handle snippets on that page, use the 
\family typewriter
StatefulSnippet.link
\family default
 method (instead of 
\family typewriter
SHtml.link
\family default
); similarly, if you need to redirect to a different page, the 
\family typewriter
StatefulSnippet
\family default
 trait defines a 
\family typewriter
redirectTo
\family default
 method.
 In either of these instances, a function map is added to the link or redirect,
 respectively, that causes the instance to be reattached.
\end_layout

\begin_layout Standard
When might you use a stateful snippet? Consider a multi-part form where
 you'd like to have a user enter data over several pages
\begin_inset Note Note
status open

\begin_layout Plain Layout
Might need a better example now that we have Screen/Wizard
\end_layout

\end_inset

.
 You'll want the application to maintain the previously entered data while
 you validate the current entry, but you don't want to have to deal with
 a lot of hidden form variables.
 Using a 
\family typewriter
StatefulSnippet
\family default
 instance greatly simplifies writing the snippet because you can keep all
 of your pertinent information around as instance variables instead of having
 to insert and extract them from every request, link, etc.
\end_layout

\begin_layout Standard
Listing 
\begin_inset CommandInset ref
LatexCommand ref
reference "lst:Using-a-StatefulSnippet"

\end_inset

 shows an example of a stateful snippet that handles the above example.
 Note that for this example, the URL (and therefore, the template) don't
 change between pages.
 The template we use is shown in Listing 
\begin_inset CommandInset ref
LatexCommand ref
reference "lst:The-StatefulSnippet-Example"

\end_inset

.
 Remember to call 
\family typewriter
unregisterThisSnippet()
\family default
 when you're finished with your workflow in order to stop the current instance
 from being used.
\end_layout

\begin_layout Standard
\begin_inset listings
inline false
status open

\begin_layout Plain Layout

\begin_inset Caption

\begin_layout Plain Layout
Using a StatefulSnippet
\begin_inset CommandInset label
LatexCommand label
name "lst:Using-a-StatefulSnippet"

\end_inset


\end_layout

\end_inset


\end_layout

\begin_layout Plain Layout

...
 standard Lift imports ...
\end_layout

\begin_layout Plain Layout

import scala.xml.Text
\end_layout

\begin_layout Plain Layout

\end_layout

\begin_layout Plain Layout

class BridgeKeeper extends StatefulSnippet {
\end_layout

\begin_layout Plain Layout

  // Define the dispatch for snippets.
 Note that we are defining
\end_layout

\begin_layout Plain Layout

  // it as a var so that the snippet for each portion of the 
\end_layout

\begin_layout Plain Layout

  // multi-part form can update it after validation.
\end_layout

\begin_layout Plain Layout

  var dispatch : DispatchIt = {
\end_layout

\begin_layout Plain Layout

    // We default to dispatching the "challenge" snippet to our
\end_layout

\begin_layout Plain Layout

    // namePage snippet method.
 We'll update this below
\end_layout

\begin_layout Plain Layout

    case "challenge" => firstPage _
\end_layout

\begin_layout Plain Layout

  }
\end_layout

\begin_layout Plain Layout

\end_layout

\begin_layout Plain Layout

  // Define our state variables:
\end_layout

\begin_layout Plain Layout

  var (name,quest,color) = ("","","")
\end_layout

\begin_layout Plain Layout

\end_layout

\begin_layout Plain Layout

  // Our first form page
\end_layout

\begin_layout Plain Layout

  def firstPage (xhtml : NodeSeq) : NodeSeq = {
\end_layout

\begin_layout Plain Layout

    def processName (nm : String) {
\end_layout

\begin_layout Plain Layout

      name = nm
\end_layout

\begin_layout Plain Layout

      if (name != "") {
\end_layout

\begin_layout Plain Layout

        dispatch = { case "challenge" => questPage _ }
\end_layout

\begin_layout Plain Layout

      } else {
\end_layout

\begin_layout Plain Layout

        S.error("You must provide a name!")
\end_layout

\begin_layout Plain Layout

      }
\end_layout

\begin_layout Plain Layout

    }
\end_layout

\begin_layout Plain Layout

    bind("form", xhtml,
\end_layout

\begin_layout Plain Layout

         "question" -> Text("What is your name?"),
\end_layout

\begin_layout Plain Layout

         "answer" -> SHtml.text(name, processName))
\end_layout

\begin_layout Plain Layout

  }
\end_layout

\begin_layout Plain Layout

\end_layout

\begin_layout Plain Layout

  def questPage (xhtml : NodeSeq) : NodeSeq = {
\end_layout

\begin_layout Plain Layout

    def processQuest (qst : String) {
\end_layout

\begin_layout Plain Layout

      quest = qst
\end_layout

\begin_layout Plain Layout

      if (quest != "") {
\end_layout

\begin_layout Plain Layout

        dispatch = { 
\end_layout

\begin_layout Plain Layout

          case "challenge" if name == "Arthur" => swallowPage _
\end_layout

\begin_layout Plain Layout

          case "challenge" => colorPage _ 
\end_layout

\begin_layout Plain Layout

        }
\end_layout

\begin_layout Plain Layout

      } else {
\end_layout

\begin_layout Plain Layout

        S.error("You must provide a quest!")
\end_layout

\begin_layout Plain Layout

      }
\end_layout

\begin_layout Plain Layout

    }
\end_layout

\begin_layout Plain Layout

    bind("form", xhtml,
\end_layout

\begin_layout Plain Layout

         "question" -> Text("What is your quest?"),
\end_layout

\begin_layout Plain Layout

         "answer" -> SHtml.text(quest, processQuest))
\end_layout

\begin_layout Plain Layout

  }
\end_layout

\begin_layout Plain Layout

\end_layout

\begin_layout Plain Layout

  def colorPage (xhtml : NodeSeq) : NodeSeq = {
\end_layout

\begin_layout Plain Layout

    def processColor (clr : String) {
\end_layout

\begin_layout Plain Layout

      color = clr
\end_layout

\begin_layout Plain Layout

      if (color.toLowercase.contains "No,") {
\end_layout

\begin_layout Plain Layout

        // This is a cleanup that removes the mapping for this
\end_layout

\begin_layout Plain Layout

        // StatefulSnippet from the session.
 This will happen 
\end_layout

\begin_layout Plain Layout

        // over time with GC, but it's best practice to manually 
\end_layout

\begin_layout Plain Layout

        // do this when you're finished with the snippet
\end_layout

\begin_layout Plain Layout

        this.unregisterThisSnippet()
\end_layout

\begin_layout Plain Layout

        S.redirectTo("/pitOfEternalPeril")
\end_layout

\begin_layout Plain Layout

      } else if (color != "") {
\end_layout

\begin_layout Plain Layout

        this.unregisterThisSnippet()
\end_layout

\begin_layout Plain Layout

        S.redirectTo("/scene24")
\end_layout

\begin_layout Plain Layout

      } else {
\end_layout

\begin_layout Plain Layout

        S.error("You must provide a color!")
\end_layout

\begin_layout Plain Layout

      }
\end_layout

\begin_layout Plain Layout

    }
\end_layout

\begin_layout Plain Layout

    bind("form", xhtml,
\end_layout

\begin_layout Plain Layout

         "question" -> Text("What is your favorite color?"),
\end_layout

\begin_layout Plain Layout

         "answer" -> SHtml.text(color, processColor))
\end_layout

\begin_layout Plain Layout

  }
\end_layout

\begin_layout Plain Layout

  // and so on for the swallowPage snippet
\end_layout

\begin_layout Plain Layout

  ...
\end_layout

\begin_layout Plain Layout

}
\end_layout

\end_inset


\end_layout

\begin_layout Standard
\begin_inset listings
lstparams "language=XML"
inline false
status open

\begin_layout Plain Layout

\begin_inset Caption

\begin_layout Plain Layout
The StatefulSnippet Example Template
\begin_inset CommandInset label
LatexCommand label
name "lst:The-StatefulSnippet-Example"

\end_inset


\end_layout

\end_inset


\end_layout

\begin_layout Plain Layout

<lift:surround with="default" at="content">
\end_layout

\begin_layout Plain Layout

  <lift:BridgeKeeper.challenge form="POST">
\end_layout

\begin_layout Plain Layout

    <form:question /> : <form:answer /> <br />
\end_layout

\begin_layout Plain Layout

    <input type="submit" value="Answer" />
\end_layout

\begin_layout Plain Layout

  </lift:BridgeKeeper.challenge>
\end_layout

\begin_layout Plain Layout

</lift:surround>
\end_layout

\end_inset


\end_layout

\begin_layout Standard
If you're using implicit dispatch (Section 
\begin_inset CommandInset ref
LatexCommand ref
reference "sub:Implicit-Dispatch-Via"

\end_inset

), then you're done.
 If you want to use explicit dispatch
\begin_inset Index
status open

\begin_layout Plain Layout
Snippets ! explicit dispatch with StatefulSnippet
\end_layout

\end_inset


\begin_inset Index
status open

\begin_layout Plain Layout
StatefulSnippet ! explicit dispatch
\end_layout

\end_inset

, however, you need to do a little more work than usual in the 
\family typewriter
LiftRules.snippetDispatch
\family default
 setup.
 Listing 
\begin_inset CommandInset ref
LatexCommand ref
reference "lst:Explicit-Dispatch-with-stateful"

\end_inset

 shows how we can bind our own StatefulSnippet classes without using reflection.
 
\end_layout

\begin_layout Standard
\begin_inset listings
inline false
status open

\begin_layout Plain Layout

\begin_inset Caption

\begin_layout Plain Layout
Explicit Dispatch with Stateful Snippets
\begin_inset CommandInset label
LatexCommand label
name "lst:Explicit-Dispatch-with-stateful"

\end_inset


\end_layout

\end_inset


\end_layout

\begin_layout Plain Layout

// In your boot method:
\end_layout

\begin_layout Plain Layout

LiftRules.snippetDispatch.append {
\end_layout

\begin_layout Plain Layout

  // S.snippetForClass checks to see if an instance has already
\end_layout

\begin_layout Plain Layout

  // registered.
 This is the case after form submission or when
\end_layout

\begin_layout Plain Layout

  // we use the StatefulSnippet.link or .redirectTo methods
\end_layout

\begin_layout Plain Layout

  case "BridgeKeeper" => S.snippetForClass("TestHello") openOr {
\end_layout

\begin_layout Plain Layout

    // If we haven't already registered an instance, create one
\end_layout

\begin_layout Plain Layout

    val inst = new com.test.TestHello
\end_layout

\begin_layout Plain Layout

    // The name is what Lift uses to locate an instance (S.snippetForClass)
\end_layout

\begin_layout Plain Layout

    // We need to add it so that the Stateful callback functions can
\end_layout

\begin_layout Plain Layout

    // self-register
\end_layout

\begin_layout Plain Layout

    inst.addName("TestHello")
\end_layout

\begin_layout Plain Layout

    // Register this instance for the duration of the request
\end_layout

\begin_layout Plain Layout

    S.overrideSnippetForClass("TestHello", inst)
\end_layout

\begin_layout Plain Layout

    inst
\end_layout

\begin_layout Plain Layout

  }
\end_layout

\end_inset


\end_layout

\begin_layout Subsection
Eager Evaluation
\begin_inset CommandInset label
LatexCommand label
name "sub:Eager-Eval"

\end_inset


\end_layout

\begin_layout Standard
As we mentioned in Section 
\begin_inset CommandInset ref
LatexCommand ref
reference "sec:Snippets"

\end_inset

, Lift processes the contents of a snippet tag after it processes the tag
 itself.
 If you want the contents of a snippet tag to be processed 
\emph on
before
\emph default
 the snippet, then you need to specify the 
\family typewriter
eager_eval
\family default

\begin_inset Index
status open

\begin_layout Plain Layout
eager eval
\end_layout

\end_inset

 attribute on the tag:
\end_layout

\begin_layout LyX-Code
<lift:Hello.world eager_eval=
\begin_inset Quotes erd
\end_inset

true
\begin_inset Quotes erd
\end_inset

>...</lift:Hello.world>
\end_layout

\begin_layout Standard
This is especially useful if you're using an embedded
\begin_inset Index
status open

\begin_layout Plain Layout
embed
\end_layout

\end_inset


\begin_inset Index
status open

\begin_layout Plain Layout
Templates ! embedded
\end_layout

\end_inset


\begin_inset Index
status open

\begin_layout Plain Layout
Tags ! embed
\end_layout

\end_inset

 template (Section 
\begin_inset CommandInset ref
LatexCommand ref
reference "sub:embed-tag"

\end_inset

).
 Consider Listing 
\begin_inset CommandInset ref
LatexCommand ref
reference "lst:Embedding-and-eager"

\end_inset

: in this case, the 
\family typewriter
eager_eval
\family default
 parameter makes Lift process the 
\family typewriter
<lift:embed />
\family default
 tag before it executes the 
\family typewriter
Hello.world
\family default
 snippet method.
 If the 
\begin_inset Quotes eld
\end_inset

formTemplate
\begin_inset Quotes erd
\end_inset

 template looks like Listing 
\begin_inset CommandInset ref
LatexCommand ref
reference "lst:The-formTemplate-template"

\end_inset

, then the 
\family typewriter
Hello.world
\family default
 snippet sees the 
\family typewriter
<hello:name />
\family default
 and 
\family typewriter
<hello:time />
\family default
 XML tags as its 
\family typewriter
NodeSeq
\family default
 input.
 If the 
\family typewriter
eager_eval
\family default
 attribute is removed, however, the Hello.world snippet sees only a 
\family typewriter
<lift:embed />
\family default
 tag that will be processed after it returns.
\end_layout

\begin_layout Standard
\begin_inset listings
lstparams "language=XML"
inline false
status open

\begin_layout Plain Layout

\begin_inset Caption

\begin_layout Plain Layout
Embedding and eager evaluation
\begin_inset CommandInset label
LatexCommand label
name "lst:Embedding-and-eager"

\end_inset


\end_layout

\end_inset


\end_layout

\begin_layout Plain Layout

<lift:Hello.world eager_eval="true">
\end_layout

\begin_layout Plain Layout

  <lift:embed what="formTemplate" />
\end_layout

\begin_layout Plain Layout

</lift:Hello.world>
\end_layout

\end_inset


\end_layout

\begin_layout Standard
\begin_inset listings
lstparams "language=XML"
inline false
status open

\begin_layout Plain Layout

\begin_inset Caption

\begin_layout Plain Layout
The formTemplate template
\begin_inset CommandInset label
LatexCommand label
name "lst:The-formTemplate-template"

\end_inset


\end_layout

\end_inset


\end_layout

\begin_layout Plain Layout

<lift:children>
\end_layout

\begin_layout Plain Layout

<hello:name />
\end_layout

\begin_layout Plain Layout

<hello:time />
\end_layout

\begin_layout Plain Layout

</lift:children>
\end_layout

\end_inset


\end_layout

\begin_layout Standard
\begin_inset Note Note
status open

\begin_layout Plain Layout
Add example of same snippet on multiple pages.
\end_layout

\end_inset


\end_layout

\begin_layout Section
\begin_inset CommandInset label
LatexCommand label
name "sec:Handling-XHTML-Attributes"

\end_inset

Handling XHTML Attributes in Snippets
\begin_inset Index
status open

\begin_layout Plain Layout
Attributes
\end_layout

\end_inset


\begin_inset Index
status open

\begin_layout Plain Layout
XML ! attribute handling
\end_layout

\end_inset


\end_layout

\begin_layout Standard
It's a common requirement that elements contain XHTML attributes to control
 things like style, provide an id, register javascript event handlers, and
 other functionality.
 Lift provides two main approaches to applying attributes to elements either
 in your snippet code or directly in the XHTML template.
\end_layout

\begin_layout Subsection
\begin_inset CommandInset label
LatexCommand label
name "sub:Direct-attr-manip"

\end_inset

Direct Manipulation in Code
\end_layout

\begin_layout Standard
You can apply attributes directly to XHTML elements using the 
\begin_inset Quotes eld
\end_inset

%
\begin_inset Quotes erd
\end_inset

 operator
\begin_inset Index
status open

\begin_layout Plain Layout
Attributes ! % operator
\end_layout

\end_inset

 to apply a
\begin_inset Newline linebreak
\end_inset


\family typewriter
scala.xml.UnprefixedAttribute
\family default
 instance
\begin_inset Foot
status open

\begin_layout Plain Layout
there's a corresponding 
\family typewriter
PrefixedAttribute
\family default
 as well
\end_layout

\end_inset

 to an element.
 Lift's 
\family typewriter
net.liftweb.util.Helpers
\family default
 trait contains an implicit conversion from a 
\family typewriter
Pair[String,_]
\family default
 to an 
\family typewriter
UnprefixedAttribute
\family default
 called 
\family typewriter
pairToUnprefixed
\family default
 that allows you to use a simpler syntax.
 You may chain invocations of 
\begin_inset Quotes eld
\end_inset

%
\begin_inset Quotes erd
\end_inset

 to apply multiple attributes.
 For example, Listing 
\begin_inset CommandInset ref
LatexCommand ref
reference "lst:Applying-Attributes-percent"

\end_inset

 shows how you can apply an 
\begin_inset Quotes eld
\end_inset

id
\begin_inset Quotes erd
\end_inset

 and 
\begin_inset Quotes eld
\end_inset

class
\begin_inset Quotes erd
\end_inset

 attribute to a text box and to a normal paragraph.
\end_layout

\begin_layout Standard
\begin_inset listings
inline false
status open

\begin_layout Plain Layout

val myInput = SHtml.text("", processText(_)) % ("id" -> "inputField") % 
\end_layout

\begin_layout Plain Layout

  ("class" -> "highlighted")
\end_layout

\begin_layout Plain Layout

\begin_inset Caption

\begin_layout Plain Layout
\begin_inset CommandInset label
LatexCommand label
name "lst:Applying-Attributes-percent"

\end_inset

Applying Attributes with 
\family typewriter
%
\end_layout

\end_inset


\end_layout

\end_inset


\end_layout

\begin_layout Standard
\align center
\begin_inset Box Shadowbox
position "t"
hor_pos "c"
has_inner_box 1
inner_pos "t"
use_parbox 0
width "75col%"
special "none"
height "1in"
height_special "totalheight"
status open

\begin_layout Plain Layout
Note that the % metadata mechanism is actually part of the Scala XML library.
 Specifically, 
\family typewriter
scala.xml.Elem
\family default
 has a 
\family typewriter
%
\family default
 method that allows the user to update the attributes on a given XML element
 by passing in a 
\family typewriter
scala.xml.UnprefixedAttribute
\family default
.
 We suggest reading more about this in the Scala API documents, or in the
 Scala XML docbook at 
\begin_inset CommandInset href
LatexCommand href
target "http://burak.emir.googlepages.com/scalaxbook.docbk.html"

\end_inset

.
 
\end_layout

\end_inset


\end_layout

\begin_layout Subsection
\begin_inset CommandInset label
LatexCommand label
name "sub:XHTML-Attribute-Pass-through"

\end_inset

XHTML Attribute Pass-through
\begin_inset Index
status open

\begin_layout Plain Layout
Attributes ! binding
\end_layout

\end_inset


\begin_inset Index
status open

\begin_layout Plain Layout
XML ! preserving attributes
\end_layout

\end_inset


\end_layout

\begin_layout Standard
The second main approach to modifying XHTML attributes is to specify them
 directly in your templates.
 This has the benefit of allowing your template designers to directly manipulate
 things like style-related attributes and keeping the markup and the logic
 separate.
 Listing 
\begin_inset CommandInset ref
LatexCommand ref
reference "lst:Snippet-mixin-attributes"

\end_inset

 shows how you can utilize the 
\begin_inset Quotes eld
\end_inset

-%>
\begin_inset Quotes erd
\end_inset


\begin_inset Index
status open

\begin_layout Plain Layout
Attributes ! -%> operator
\end_layout

\end_inset

 binding operator instead of 
\begin_inset Quotes eld
\end_inset

->
\begin_inset Quotes erd
\end_inset

 to preserve attributes.
\end_layout

\begin_layout Standard
\begin_inset listings
inline false
status open

\begin_layout Plain Layout

\begin_inset Caption

\begin_layout Plain Layout
Snippet mixin attributes 
\begin_inset CommandInset label
LatexCommand label
name "lst:Snippet-mixin-attributes"

\end_inset


\end_layout

\end_inset


\end_layout

\begin_layout Plain Layout

// the markup
\end_layout

\begin_layout Plain Layout

<lift:Ledger.balance>
\end_layout

\begin_layout Plain Layout

  <ledger:time id="myId"/>
\end_layout

\begin_layout Plain Layout

</lift:Ledger.balance>
\end_layout

\begin_layout Plain Layout

\end_layout

\begin_layout Plain Layout

// The snippet class
\end_layout

\begin_layout Plain Layout

\end_layout

\begin_layout Plain Layout

class Ledger {
\end_layout

\begin_layout Plain Layout

  def balance (content : NodeSeq ) : NodeSeq = {
\end_layout

\begin_layout Plain Layout

    bind ("ledger", content,
\end_layout

\begin_layout Plain Layout

          "time" -%> <span>{(new java.util.Date).toString}</span>)
\end_layout

\begin_layout Plain Layout

  }
\end_layout

\begin_layout Plain Layout

}
\end_layout

\end_inset


\end_layout

\begin_layout Standard
The resulting node will be something like
\end_layout

\begin_layout LyX-Code

\family typewriter
<span id=
\begin_inset Quotes erd
\end_inset

myId
\begin_inset Quotes erd
\end_inset

>Sat Mar 28 16:43:48 EET 2009</span>
\end_layout

\begin_layout Standard
In addition to the 
\begin_inset Quotes eld
\end_inset

-%>
\begin_inset Quotes erd
\end_inset

 binding operator, there is also the 
\begin_inset Quotes eld
\end_inset

_id_>
\begin_inset Quotes erd
\end_inset

 
\begin_inset Index
status open

\begin_layout Plain Layout
_id_> operator
\end_layout

\end_inset

operator, which uses the element's name as its 
\begin_inset Quotes eld
\end_inset

id
\begin_inset Quotes erd
\end_inset

 attribute.
 Listing shows a snippet method using the 
\begin_inset Quotes eld
\end_inset

_id_>
\begin_inset Quotes erd
\end_inset

 attribute and Listing shows the resulting markup.
\end_layout

\begin_layout Standard
\begin_inset listings
inline false
status open

\begin_layout Plain Layout

\begin_inset Caption

\begin_layout Plain Layout
\begin_inset CommandInset label
LatexCommand label
name "lst:Binding-with-the_id_"

\end_inset

Binding with the _id_> operator
\end_layout

\end_inset


\end_layout

\begin_layout Plain Layout

def idByName (xhtml : NodeSeq) : NodeSeq = 
\end_layout

\begin_layout Plain Layout

  bind("example", xhtml, "name" _id_> <span>Fred</span>)
\end_layout

\end_inset


\end_layout

\begin_layout Standard
\begin_inset listings
lstparams "language=XML"
inline false
status open

\begin_layout Plain Layout

\begin_inset Caption

\begin_layout Plain Layout
\begin_inset CommandInset label
LatexCommand label
name "lst:Markup-bound-using_id_"

\end_inset

Markup bound using _id_>
\end_layout

\end_inset


\end_layout

\begin_layout Plain Layout

<!-- Input: -->
\end_layout

\begin_layout Plain Layout

<lift:HelloWorld.idByName>
\end_layout

\begin_layout Plain Layout

  Hi, <example:name /> 
\end_layout

\begin_layout Plain Layout

</lift:HelloWorld.idByName>
\end_layout

\begin_layout Plain Layout

\end_layout

\begin_layout Plain Layout

<!-- Output: -->
\end_layout

\begin_layout Plain Layout

Hi, <span id="name">Fred</span> 
\end_layout

\end_inset


\end_layout

\end_body
\end_document