User Guide : wxRuby Extensions
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The Keyword Constructors extension allows the use of Ruby hash-style keyword arguments in constructors of common WxWidgets Windows, Frame, Dialog and Control classes.
Building a GUI in WxWidgets involves lots of calls to new, but
these methods often have long parameter lists. Often the default
values for many of these parameters are correct. For example, if
you're using a sizer-based layout, you usually don't want to specify a
size for widgets, but you still have to type
Wx::TreeCtrl.new( parent, -1, Wx::DEFAULT_POSITION, Wx::DEFAULT_SIZE, Wx::NO_BUTTONS )
just to create a standard TreeCtrl with the 'no buttons' style. If you want to specify the 'NO BUTTONS' style, you can't avoid all the typing of DEFAULT_POSITION etc.
With keyword_constructors, you could write the above as
TreeCtrl.new(parent, :style => Wx::NO_BUTTONS)
And it will assume you want the default id (-1), and the default size and position. If you want to specify an explicit size, you can do so:
TreeCtrl.new(parent, :size => Wx::Size.new(100, 300))
For brevity, this module also allows you to specify positions and sizes using a a two-element array:
TreeCtrl.new(parent, :size => [100, 300])
Similarly with position:
TreeCtrl.new(parent, :pos => Wx::Point.new(5, 25))
TreeCtrl.new(parent, :pos => [5, 25])
You can have multiple keyword arguments:
TreeCtrl.new(parent, :pos => [5, 25], :size => [100, 300] )
As with position and size, you usually don't want to deal with
assigning unique ids to every widget and frame you create - it's a C++
hangover that often seems clunky in Ruby. The Event Handling
extensions allows you to set up event handling without having to use
ids, and if no :id argument is supplied to a constructor, the default
(-1) will be passed. This will allocate a unique ID for the window
automatically (all such automatically-assigned IDs are negative and so
will not conflict with any user-defined IDs as long as they are positive).
There are occasions when a specific ID does need to be used - for example, to tell WxWidgets that a button is a 'stock' item, so that it can be displayed using platform-standard text and icon. To do this, simply pass an :id argument to the constructor - here, the system's standard 'preview' button
Wx::Button.new(parent, :id => Wx::ID_PREVIEW)
The arguments :size, :pos and :style are common to many WxWidgets
window classes. The new methods of these classes also have
parameters that are specific to those classes; for example, the text
label on a button, or the initial value of a text control.
Wx::Button.new(parent, :label => 'press me')
Wx::TextCtrl.new(parent, :value => 'type some text here')
The keyword names of these arguments can be found by looking at the
WxRuby documentation, in the relevant class's new method. You can
also get a string description of the class's new method parameters
within Ruby by doing:
puts Wx::TextCtrl.describe_constructor()
This will print a list of the argument names expected by the class's
new method, and the correct type for them.
To support existing code, and to avoid forcing the use of more verbose
keyword-style arguments where they're not desired, you can mix
positional and keyword arguments, omitting or including ids as
desired.
Wx::Button.new(parent, 'press me', :style => Wx::BU_RIGHT)
To support complex (context dependent) defaults and/or auto conversion of arguments for backwards compatibility the keyword constructors extension allows the definition of lambdas or procs to be associated with a parameter specification.
The wxWidgets API, in typical C++ style, has lots of accessor methods like
GetPosition()SetSize(a_size)IsChecked()CanUndo()HasStyle(a_style)
which in wxRuby are mapped to Ruby methods like get_position, set_size etc.
In Ruby however these kind of methods that set, get or query attributes or state are normally simply called by the attribute name or, in other cases, by a predicate method like:
pos = frame.position
frame.size = a_size
item.checked?
control.can_undo?
window.has_style?(a_style)With wxRuby3 (most of) the API methods that begin with get_, set_, is_, can_ and has_ are identified
and the wxRuby API will have Ruby-style accessor aliases defined for those (appropriately decorated as needed).
Note that if you are calling a 'setter' method on self, you must explicitly send the message to self like:
# set's self size to be 100px by 100px
self.size = Wx::Size.new(100, 100)since this will not work as you expect it to:
# only sets the value of a local variable 'size'
size = Wx::Size.new