Instantiating sub widgets

The method initializeWidgets is used to instantiate the different widgets that are part of the UI and store them in their respective instance variables. The configuration and default values of each widget are specified here as well. This focus in this method is to specify what the widgets will look like and what their self-contained behavior is. The behavior to update model state, e.g. when pressing a Save button, is described in this method as well. It is explicitly not the responsibility of this method to define the interactions between the widgets.

In general the initializeWidgets method should follow the pattern:

• widgets instantiation
• widgets configuration specification
• specification of order of focus

The last step is not mandatory but highly recommended. Indeed, without this final step keyboard navigation will not work at all.

The code in figure pattern shows an example of an initializeWidgets method. It first instantiates a button and a list widget, storing each in an instance variable. It second configures the button it by setting its label. Third it specifies the focus order of all the widgets: first the button and then the list.

initializeWidgets

    theButton := self newButton.
    theList := self newList.

    theButton label: 'I am a button'.
    theList items: #(1 2 3 4 5 6 7 8 9 0).
    
    self focusOrder
        add: theButton;
        add: theList.

Widget instantiation

The instantiation of a widget can be done in two ways: through the use of an creation method or through the use of the instantiate: method.

Considering the first option, the framework provides unary messages for the creation of all basic widgets. The format of these messages is new[Widget], for example newButton creates a button widget, and newList creates a list widget, as we have seen above. The complete list of available widget creation methods can be found in the class ComposableModel in the protocol widgets.

Considering the second option, to reuse any composite widgets, i.e. a subclass of ComposableModel, the widget needs to be initialized using the instantiate: method. For example, to reuse a MessageBrowser widget, the code is self instantiate: MessageBrowser.