WxRuby Extensions - Keyword Constructors

The *Keyword Constructors* extension allows the use of Ruby hash-style keyword arguments in constructors of common WxWidgets Windows, Frame, Dialog and Control classes.

Introduction

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.

Basic Keyword Constructors

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] )

No ID required

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 Connectors* extension 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.

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)

Class-specific arguments

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.

Mixing positional and keyword arguments

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 +id+s as desired.

Wx::Button.new(parent, 'press me', :style => Wx::BU_RIGHT)

From wx/keyword_defs.rb

WxSugar - Keyword Constructors Classes

This extension defines the keyword parameters for new methods for widgets, windows and frames. It’s for use with *Keyword Constructors* and is no use on its own - except if you are looking for a bug or want to add a missing class.

For each class, the parameters must be declared in the order that they are supplied to wxRuby. A parameter is specified by a symbol name, and, optionally, a default argument which will of whatever type the wxRuby core library accepts. Because hashes are unordered in Ruby 1.8, if a default argument is specified, this must be the last in a list of parameters.

Some common parameters to constructors such as size, position, title, id and so forth always have a standard default argumnet, which is defined in keyword_ctors. In these cases, it is not necessary to supply the default argument in the definition.