Smalltalk and Object Orientation: an Introduction - Free

instanceVariableNames: ''
classVariableNames: ''
poolDictionaries: ''
category: ‘BoxDraw’
Note that I have put this class in a category called BoxDraw. Also note that I have not had to define
any new instance or class variables - it is not necessary as I i nherit all I need from DrawingEditor. In
fact I am not even going to define any instance methods for this class. So why have a BoxDrawEditor
class at all? Because I want a different set of tools in the toolPalette.
21.4.2 Define the set of tools to use
The next s tep is therefore to define the set of tools available to a user of BoxDraw. This is done by
defining a method called defaultTools on the class side. This method is used to create the
ToolPaletteView. This method returns an OrderedCollection of creationTools. Every
type of figure will provide a creation tool for example:
LineFigure creationTool.
We are going to use the default set of tools, with the addition of just one figure, called
BoxDrawFigure. We can therefore use the defaultTools method defined in t he superclass of
BoxDrawEditor and just add a creation tool for BoxDrawFigure to the end of this
OrderedCollection. The code for this method is listed below:
defaultTools
"Answer an OrderedCollection of the tools I can use"
^(super defaultTools) add: (BoxDrawFigure creationTool); yourself.
This method should be defined in a class method category called “defaults”.
21.4.3 An example class method
Finally, for the BoxDrawEditor class we shall define a class method protocol called “examples”. In
this protocol we shall define a single method called example1. This method will send the message
open to the BoxDrawEditor which will create a new instance of the BoxDrawEditor and will
cause the graphic editor we are constructing to be displayed.
example1
BoxDrawEditor open.
21.5 BoxDrawFigure
21.5.1 Defining the figure
We now have a drawing editor for BoxDraw with everything we need defined - except what a
BoxDrawFigure is. This is the next step.
We could make a BoxDrawFigure a subclass of a simple figure such as Rectangle, Ellipse
or PolylineFigure. However, we want to have a text field in the middle of BoxDrawFigure
which will represent the name of the figure. This means that BoxDrawFigure will have at least one
subfigure, we therefore want to make BoxDrawFigure a subclass of CompositeFigure.
A CompositeFigure is a figure which possesses subfigures, who determine part or all of the
look of the figure. CompositeFigures are also often used if it is necessary to give a user access to
the subfigures (for example to change the text in the text field of the BoxDrawFigure). The
definition for BoxDrawFigure is given below:
CompositeFigure subclass: #BoxDrawFigure
instanceVariableNames: ''
classVariableNames: ''
poolDictionaries: ''
category: 'BoxDraw'
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