Smalltalk and Object Orientation: an Introduction - Free

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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 250
The next method we shall consider is the setBoxStyle method. This method is executed when the Box button is selected. This method sends the style: message to the drawingModel with the parameter #box. That is, it causes the current graphic object style to be set to #box. setBoxStyle drawingModel style: #box. In addition there are two other methods which set the style of object to be added. These are setCircleStyle and setPointStyle. They are exactly t he same as the setBoxStyle method except that they pass the symbols #circle and #point to the drawingModel via the message style: . The setCircleStyle method is called whenever the Circle button is selected and the setPointStyle method whenever the Point button is selected: setCircleStyle drawingModel style: #circle. setPointStyle drawingModel style: #point. Finally the aspects protocol (automatically generated for you if you have used the definer) will contain a single method called drawingView. This is an accessor method for the aspect drawingView: drawingView ^drawingView As usual the SmallDraw application is instantiated by sending the message SmallDraw. For example: open to the class 29.5.2 The DrawingModel class SmallDraw open The DrawingModel class is a subclass of Model. It possesses two instance variables nodes and style. The instance variable style indicates the type of object to add to the collection of objects in nodes. The class definition is: Model subclass: #DrawingModel instanceVariableNames: 'nodes style ' classVariableNames: '' poolDictionaries: '' category: 'SmallDraw' The DrawingModel class comment is left as an exercise for the reader. Having defined the DrawingModel class and class comment we are now ready to define the initialize method. As usual we will place this method in an initialize method protocol. The initialize method initializes the two instance variables nodes and style. A new ordered collection is instantiated for the first and the style: accessor method is used to set the second (with a default style of #box): initialize nodes := OrderedCollection new. self style: #box. We are now ready to define the accessing methods for DrawingModel. These methods (defined within an accessing protocol) access the instance variabl es of the class. For example, nodes and style retrieve the value of their associated instance variables, while style: resets the instance variable style. nodes ^nodes. style ^style style: aSymbol 251
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Smalltalk and Object Orientation: A
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Chapter 7: Smalltalk Constructs Thi
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The user interface construction fac
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Preface 1. INTRODUCTION TO OBJECT O
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12.5 A CLASS SIDE METHOD...........
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27.3 VISUALWORKS WINDOW PAINTING TO
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Part One Introduction to Object Ori
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interfaces between different parts
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een to ease the transition from one
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encapsulation. Attempting to introd
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is a controversial subject which is
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will become second nature to many o
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or return something. It has since b
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defining the behavior of different
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In time most developers start to ac
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2.4.3.4 Smalltalk environments are
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3. Constructing an Object Oriented
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Wash wipe switch Wiper motor Relay
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Point 2 above is more complicated.
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services working? working? working?
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Part Two The Smalltalk Language 42
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other systems. As the browsers, ins
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VisualAge (a version of Smalltalk w
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4.5.2 The VisualWorks Launcher and
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Class categories. These are group s
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5. A Little Smalltalk 5.1 Introduct
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Notifiers can be displayed under a
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These concepts of messages, receive
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Select the “Debug” option. This
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6. Smalltalk Building Blocks 6.1 In
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6.3.1 Class definitions In Smalltal
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Object Class1 Class 2 method search
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“Now calculate y “ y := x * 23.
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7. Smalltalk Constructs 7.1 Introdu
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They are more efficient for storage
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7.5.3 true, false and nil variables
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anArray at: 1 max: 10. This will tr
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Figure 8.1: Defining a new class 8.
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this convention at the moment, howe
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9. Control and Iteration 9.1 Introd
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9.3.3 Block temporary variables Blo
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The brackets round the 1 to: 10 are
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OrderedCollection class (respective
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holding other objects. Typically, c
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| temp | temp := Set new. temp add:
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Next we will define a message proto
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11. Further Collection Classes 11.1
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for (i = 0; i
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x inspect. This has some similariti
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11.9.3 The reject: message The reje
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• asSortedCollection. This create
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Figure 12.2: The Organizer class de
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12.6 The private-updating protocol
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do: [:item | Transcript show: item
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13. Streams and Files 13.1 Introduc
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Notice that in this example we used
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to reconstruct the data into object
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1. The ability to save the current
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14.3 The class Date Class Date, a s
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aCharacter isAlphabetic. aCharacter
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Breakpoints may be placed in a me t
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If the file does not exist you will
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Figure 15.4: Creating a project To
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Part Three Object Oriented Design 1
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16. Object Oriented Analysis and De
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devolved amongst the objects). This
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driving force behind the whole of t
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17. The Unified Modeling Language 1
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Deployment diagrams . Deployment di
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Window abstract +size : Area = (10,
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Micro Computer 1.. * Monitor System
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connectedTo * Lamp * Weight Sensor
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18. UML: Dynamic Modeling And Deplo
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edisplay() Controller window A Wind
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18.2.3.1 A start point A start poin
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etween nodes and their stereotype.
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OMT is a prescriptive method, it pr
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confirming the users’ needs, thei
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19.3.2.2 Prepare a data dictionary
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car, truck and bus under a supercla
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20.2.1.3 Prepare sequence and colla
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20.2.2.5 Specify optimization crite
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are therefore concurrent and can be
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20.3.2.3 Design optimization The an
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21. Frameworks and Patterns for Obj
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As the framework takes shape you sh
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about a set of classes, than to att
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instanceVariableNames: '' classVari
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21.5.5 Running the editor You have
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Part Four Testing and Style 181
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made worse, because the symbol held
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22.3.2 Incremental testing Incremen
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control the execution of the method
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22.7.2 The Perform: message The per
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From the scenario that a person mig
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23.4 Self testing An approach, sugg
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24. Smalltalk Style Guidelines 24.1
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24.2.4 Adding variables to system c
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