Exercise A101 in Visual Basic .NET

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Exercise A101
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Add a new button to the main form, give it the name btnAnalog and the caption Analog Clock Now add code to cause it to create an AnalogTimeObserver and attach it to the Timekeeper object (the code will be very similar to the code to attach the digital clock)
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Just for fun, the code shown in Listing A1015 can be placed on another form that has controls and properties exactly like the AnalogTimeObserver (remove the control box from the form, give it a name (BlobTimeObserver), and a panel with the name pnBlobs, and set its Dock property to Fill It will produce an unusual clock face for anyone who is bored with easy time-telling Having added the form, remember to add a button to create instances of it
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Public Class BlobTimeObserver Inherits SystemWindowsFormsForm Implements ITimeObserver Private x_6 As Integer, x_2 As Integer, x_5_6 As Integer Private y_2 As Integer
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Practical Activities
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Public Sub Notify(ByVal T As MultiClockTimekeeper) _ Implements MultiClockITimeObserverNotify Dim hourBlob As Rectangle, hourSize As Size Dim minBlob As Rectangle, minSize As Size Dim secBlob As Rectangle, secSize As Size Dim xs, ys As Single SetSize() xs = x_6 * THour / 12 ys = y_2 * THour / 12 hourBlob = New Rectangle(x_6 xs, y_2 ys, _ xs + xs, ys + ys) xs = x_6 * TMinute / 60 ys = y_2 * TMinute / 60 minBlob = New Rectangle(x_2 xs, y_2 ys, _ xs + xs, ys + ys) xs = x_6 * TSecond / 60 ys = y_2 * TSecond / 60 secBlob = New Rectangle(x_5_6 xs, y_2 ys, _ xs + xs, ys + ys) Dim g As Graphics = pnlBlobsCreateGraphics() Dim drawFont As New Font("Arial", 16) Dim drawBrush As New SolidBrush(ColorBlack) Dim textRect As New RectangleF(x_6 20, _ y_2 10, 40, 20) gClear(ColorWhite) gFillEllipse(BrushesBlue, hourBlob) gDrawString(THourToString("00"), drawFont, _ drawBrush, textRect) gFillEllipse(BrushesYellow, minBlob) textRectX = x_2 20 gDrawString(TMinuteToString("00"), drawFont, _ drawBrush, textRect) gFillEllipse(BrushesRed, secBlob) textRectX = x_5_6 20 gDrawString(TSecondToString("00"), drawFont, _ drawBrush, textRect) End Sub Private Sub SetSize() x_6 = pnlBlobsWidth / 6 x_2 = pnlBlobsWidth / 2 x_5_6 = pnlBlobsWidth x_6 y_2 = pnlBlobsHeight / 2 End Sub Public Sub Kill() Implements MultiClockITimeObserverKill MeClose() MeDispose() End Sub End Class Listing A1015: Another ITimeObserver form
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10 n Object Modelling
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Figure A103
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One timekeeper, several observers
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The resulting application is shown in Figure A103, with four observer instances in operation
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Features worth remembering
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In this chapter, we ve looked at a range of areas that broadly address the ideal of building object models In programs that you go on to create, you should consider the following
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Patterns are templates for code devised by experts On your way to becoming an expert, you should always be on the lookout for established ways of doing things The book on patterns mentioned earlier in the chapter is an important resource to very many professional programmers, and there are lots of websites which now contain material speci cally on patterns in Visual Basic The code in an application will only be as good as the structure it is applied to While it is possible to create a program that has a badly thought out structure and get it working, it will always be much more dif cult to maintain that type of program Learn the established structures and what situations they are used in Managing resources in NET is easier than in most programming environments, since garbage collection takes care of most of the objects you will ever create However, you should be aware that some resources (usually external resources such as les, database, network connections, etc) are not managed by NET and you should keep the general approach to the Dispose() method in your armoury
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Solutions to Exercises
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for when you need to release resources in a timely manner Beware though, that you should not normally deal with managed resources in this way since that could make your application less ef cient
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