Smalltalk and Object Orientation: an Introduction - Free

29.5 The classes involved
This section describes how to implement the classes in the SmallDraw application in detail (see Figure
29.4 which illustrates the classes in this application). We will first consider the SmallDraw application
itself before considering the three classes involved in the MVC framework ( DrawingModel,
DrawingView and DrawingController) and wi ll conclude by describing the “widget” classes:
DrawingWidget, PointWidget, CircleWidget and PointWidget.
29.5.1 The SmallDraw class
The SmallDraw class is a subclass of ApplicationModel. It possesses two instance variables,
drawingView (which is actually an aspe ct referencing the custom view) and drawingModel. The
class definition is presented below and can be typed in using the System Browser. Note that this
assumes that the class is being defined in a class category called SmallDraw.
ApplicationModel subclass: #SmallDraw
instanceVariableNames: 'drawingView drawingModel '
classVariableNames: ''
poolDictionaries: ''
category: 'SmallDraw'!
The SmallDraw application provides the main window for the application. It possesses four buttons, and
a view as illustrated in Figure 29.10. You should use the canvas tool and the palette to create a window
which resembles this. Next use the properties tool to define the properties for the four buttons and the
view. The figure illustrates the actions defined for each button and the aspect name of the custom view.
Action: setPointStyle
Action: setBoxStyle
Action: setCircleStyle
Action: exit
View: drawingView
Figure 29.10: Defining the graphic elements of the SmallDraw application
Next use the definer tool from t he canvas tools Launcher to create stub methods for the actions
illustrated in Figure 29.10.
We shall now define the initialize method in the initialize protocol in the SmallDraw class
(use a browser to do this). The initialize method creates an instance of the DrawingView class,
the DrawingModel class and links them together. The method is presented below:
initialize
drawingView := DrawingView new.
drawingModel := DrawingModel new.
drawingView model: drawingModel.
You are now ready to define each of the action methods in the actions protocol. The first method we
shall consider is the exit method which is executed when the exit button is selected. This message
uses the closeRequest method we saw in the last chapter to terminate the application:
exit
self closeRequest
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