VISUAL BASIC CONTROL FUNDAMENTALS in VS .NET

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VISUAL BASIC CONTROL FUNDAMENTALS
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EXAMPLE 4.13 USING SCROLL BARS (THE METRONOME REVISITED)
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In this example we again consider the metronome that was originally presented in Example 4.12. Now, however, we will use a horizontal scroll bar rather than a text box to specify the tempo. Fig. 4.42 shows the initial control layout. Comparing this figure with Fig. 4.38, we see that the label has been raised, and the horizontal scroll bar, named HScroll1, has been placed in the location formerly occupied by the text box.
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Fig. 4.42
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We now assign the following initial values to the control properties. Object Form1 Shape1 Property Caption Shape FillColor FillStyle Shape FillColor FillStyle Enabled Caption Font Min Max SmallChange LargeChange Value Caption Font Caption Font Caption Font Value Metronome 3 (Circle) Red 1 (Transparent default value) 3 (Circle) Red 1 (Transparent default value) False (none) MS Sans Serif, 10-point 40 220 1 10 40 Go MS Sans Serif, 10-point Stop MS Sans Serif, 10-point End MS Sans Serif, 10-point
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Timer Label1 HScroll1
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VISUAL BASIC CONTROL FUNDAMENTALS
Note that the initial values assigned to HScroll1.Min (40) and HScroll1.Max (220) define the lower and upper limits for the tempo. The resulting Form Design Window is shown in Fig. 4.43.
The required event procedures are shown below. The first event procedure, Form_Load, causes the initial tempo (as specified by Hscroll1.Value) to be displayed on the form as Label1. The second event procedure, Hscroll1_Change, resets the tempo shown as Label1 whenever the user clicks on the horizontal scroll bar. The next event procedure, Timer1_Timer, alternates the flashing circles in exactly the same manner as in the previous example. Command1_Click is now simpler, because we no longer need to provide an error trap for tempos that are out of range. The horizontal scroll bar does this for us, with the values assigned to HScroll1.Min and HScroll1.Max. Hence Command1_Click now accepts the tempo directly from the current value of HScroll1.Value, then determines a value for the timer interval and enables the timer. The remaining two event procedures, Command2_Click and Command3_Click, are similar to their counterparts in the earlier example.
Private Sub Form_Load() Label1.Caption = Str(HScroll1.Value) End Sub Private Sub HScroll1_Change() Label1.Caption = Str(HScroll1.Value) End Sub Private Sub Timer1_Timer() 'Beep If (Shape1.FillStyle = Shape1.FillStyle = Shape2.FillStyle = Else Shape1.FillStyle = Shape2.FillStyle = End If End Sub
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Fig. 4.43
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VISUAL BASIC CONTROL FUNDAMENTALS
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Private Sub Command1_Click() Dim Tempo As Single Tempo = HScroll1.Value Timer1.Interval = 60 * (1000 / Tempo) Timer1.Enabled = True End Sub Private Sub Command2_Click() Timer1.Enabled = False End Sub Private Sub Command3_Click() End End Sub
When the program is executed, the user will specify a tempo with the horizontal scroll bar. Clicking on the Go button then results in the flashing display illustrated in Fig. 4.44. At any time the user may click on the Stop button, reset the tempo, and again click on Go, thus restarting the metronome at a different tempo. Clicking on the End button will terminate the computation.
Fig. 4.44
Review Questions
4.1 4.2 What is the purpose of the Visual Basic toolbox What is the purpose of each of the following Visual Basic tools (a) (b) (c) (d) (e) (f) Check box Combo box Command button Horizontal scroll bar Frame Image box (g) (h) (i) (j) (k) (l) Label List box Option button Picture box Text box Vertical scroll bar
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VISUAL BASIC CONTROL FUNDAMENTALS
4.3 4.4 4.5 4.6 4.7
Describe two different methods for adding a control to the Form Design Window. How is a control relocated within the Form Design Window How is a control resized within the Form Design Window How is a control removed from the Form Design Window Describe, in general terms, the default naming system used with Visual Basic controls within a Form Design Window. What is the recommended procedure for overriding the default naming system used with Visual Basic controls Under what conditions is it generally advisable to override the default naming system used with Visual Basic controls
4.8 4.9
4.10 How are values assigned to Visual Basic control properties at design time 4.11 How are values assigned to Visual Basic control properties during run time 4.12 What is an event procedure How does an event procedure begin and end 4.13 What is the relationship between an event procedure and a command button 4.14 Can event procedures be associated with Visual Basic controls other than command buttons 4.15 How is an event procedure created, viewed or edited 4.16 How do labels and text boxes differ from each other 4.17 How are numerical values entered and displayed in text boxes 4.18 How do check boxes and option buttons differ from each other 4.19 How is a check box disabled (i.e., grayed out ) 4.20 Can an option button be disabled (i.e., grayed out ) 4.21 What is the purpose of a frame How does the inclusion of frames affect groups of option buttons 4.22 Can check boxes be placed in a frame 4.23 How do list boxes and combo boxes differ from each other 4.24 How are new items added to a list or combo box 4.25 What is the purpose of the ListIndex property Which controls support this property How might it be used 4.26 What is the purpose of the ListCount property How might it be used 4.27 What is the purpose of the With block What advantages are provided by its use 4.28 What is the purpose of the MsgBox function How is this function used within a Visual Basic program 4.29 For what types of applications is the timer control intended 4.30 When using a timer control, what is the purpose of the Interval property What restrictions apply to its use 4.31 When using a timer control, how is the Enabled property used to start and stop the timer
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