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#LyX 1.6.1 created this file. For more info see http://www.lyx.org/
\lyxformat 345
\begin_document
\begin_header
\textclass book
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\language english
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\paperorientation landscape
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\quotes_language english
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\papersides 1
\paperpagestyle default
\tracking_changes false
\output_changes false
\author ""
\author ""
\end_header
\begin_body
\begin_layout Chapter
Message Handling
\begin_inset CommandInset label
LatexCommand label
name "cha:Message-Handling"
\end_inset
\end_layout
\begin_layout Standard
When we talk about message handling in Lift, we're talking about how you
provide feedback to the users of your application.
While there are already a lot of mechanisms for displaying data to the
user via snippets, views, etc, properly binding and setting up HTML-level
elements can get complicated, especially when you're dealing with callback
functions or error handling.
Lift provides an alternate mechanism for displaying messages to users that
is easy to use and allows flexibility in display on the client side.
\end_layout
\begin_layout Section
Sending Messages
\end_layout
\begin_layout Standard
Messages for non-Comet requests are handled via the S object (yes, even
Ajax is handled automatically); specifically, the error, notice and warning
methods allow you to send a String or a NodeSeq back to the user for display,
with or without an association with a particular element id.
The error method also provides an overload that takes a List[FieldError],
the type returned from Mapper field validation (section
\begin_inset CommandInset ref
LatexCommand ref
reference "sub:Mapper-Validation"
\end_inset
).
The messages that you send are held by a RequestVar (section
\begin_inset CommandInset ref
LatexCommand ref
reference "sec:Session-and-Request"
\end_inset
) in the S object, so you can send messages from anywhere in your stateful
request/response lifecycle without breaking the flow of your code.
Listing
\begin_inset CommandInset ref
LatexCommand ref
reference "lst:Using-messages-in-forms"
\end_inset
shows how you could use messages in form processing to send feedback on
missing fields.
\end_layout
\begin_layout Standard
\begin_inset listings
inline false
status open
\begin_layout Plain Layout
\begin_inset Caption
\begin_layout Plain Layout
Using messages in form processing
\begin_inset CommandInset label
LatexCommand label
name "lst:Using-messages-in-forms"
\end_inset
\end_layout
\end_inset
\end_layout
\begin_layout Plain Layout
object data extends RequestVar[String]("")
\end_layout
\begin_layout Plain Layout
\end_layout
\begin_layout Plain Layout
def addNote (xhtml : NodeSeq) : NodeSeq = {
\end_layout
\begin_layout Plain Layout
def doAdd () = {
\end_layout
\begin_layout Plain Layout
//validate
\end_layout
\begin_layout Plain Layout
if (data.is == "") {
\end_layout
\begin_layout Plain Layout
S.error("noteField", "You need to provide a note")
\end_layout
\begin_layout Plain Layout
} else {
\end_layout
\begin_layout Plain Layout
Note.create.note(data).save
\end_layout
\begin_layout Plain Layout
S.notice("Note added")
\end_layout
\begin_layout Plain Layout
redirectTo("/viewNotes")
\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
"note" -> SHtml.text(data.is, data(_), "id" -> "noteField"),
\end_layout
\begin_layout Plain Layout
"add" -> SHtml.submit("Add", doAdd))
\end_layout
\begin_layout Plain Layout
}
\end_layout
\end_inset
\end_layout
\begin_layout Standard
In this particular case we use two different messages.
One is an error to be displayed when the form is re-shown; this error is
associated with the
\begin_inset Quotes eld
\end_inset
noteField
\begin_inset Quotes erd
\end_inset
element.
The second message is a simple notice to let the user know that the data
was successfully saved.
\end_layout
\begin_layout Standard
For Comet
\begin_inset Index
status open
\begin_layout Plain Layout
Comet
\end_layout
\end_inset
the only difference in sending messages is that the error, notice and warning
methods are defined in the CometActor class, so you just use those directly
and Lift handles the rest.
\end_layout
\begin_layout Section
Displaying Messages
\end_layout
\begin_layout Standard
The display of messages is handled by two builtin snippets, <lift:Msgs/>
and <lift:Msg/>.
The Msgs snippet displays all messages not associated with a particular
element Id.
The messages are displayed as an unordered list, but Lift allows customization
of the messages via XML that you embed within the snippet.
For each of the three message types, you can specify a <lift:TYPE_msg>
and <lift:TYPE_class> element that controls the message label and CSS class,
respectively.
The default label is simply the title-case type (Error, Notice, Warning).
For example, listing
\begin_inset CommandInset ref
LatexCommand ref
reference "lst:Custom-message-labels"
\end_inset
shows how we could change the error and notice messages.
\end_layout
\begin_layout Standard
\begin_inset listings
inline false
status open
\begin_layout Plain Layout
\begin_inset Caption
\begin_layout Plain Layout
Custom message labels
\begin_inset CommandInset label
LatexCommand label
name "lst:Custom-message-labels"
\end_inset
\end_layout
\end_inset
\end_layout
\begin_layout Plain Layout
<lift:Msgs>
\end_layout
\begin_layout Plain Layout
<lift:error_msg>Danger, Will Robinson! </lift:error_msg>
\end_layout
\begin_layout Plain Layout
<lift:error_class>redtext</lift:error_class>
\end_layout
\begin_layout Plain Layout
<lift:notice_msg>FYI: </lift:notice_msg>
\end_layout
\begin_layout Plain Layout
</lift:Msgs>
\end_layout
\end_inset
\end_layout
\begin_layout Standard
The Msg snippet is used to display all messages associated with a particular
Id by specifying the id attribute on the <lift:Msg/> element.
With Msg, you don't get a message label, so there's no override mechanism
for it.
You do, however, have the ability to to change the message class on a per-type
basis by setting the noticeClass, errorClass, or warningClass attributes
on the <lfit:Msg/> element.
Listing
\begin_inset CommandInset ref
LatexCommand ref
reference "lst:Per-id-messages"
\end_inset
shows usage of Msg corresponding to our snippet in listing
\begin_inset CommandInset ref
LatexCommand ref
reference "lst:Using-messages-in-forms"
\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
Per-id messages
\begin_inset CommandInset label
LatexCommand label
name "lst:Per-id-messages"
\end_inset
\end_layout
\end_inset
\end_layout
\begin_layout Plain Layout
<lift:Stuff.addNote form=
"
POST
"
>
\end_layout
\begin_layout Plain Layout
<form:note /><lift:Msg id=
"
noteField
"
errorClass=
"
redtext
"
/>
\end_layout
\begin_layout Plain Layout
<form:add />
\end_layout
\begin_layout Plain Layout
</lift:Stuff.addNote>
\end_layout
\end_inset
\end_layout
\end_body
\end_document
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