Visual Basic in 12 Easy Lessons vel12.htm

• What You'll Learn
• Option Buttons Offer Choices
• Check Boxes Offer More Choices
• Multiple Sets of Option Buttons
• Control Arrays Simplify
• Homework
  • General Knowledge
  • Write Code That...
  • Extra Credit

Lesson 6, Unit 12

Checks, Options, and Control Arrays

What You'll Learn

• Option buttons offer choices
  
  
• Check boxes offer more choices
  
  
• Option buttons come in multiple sets
  
  
• Control arrays simplify programming
  
  

You'll find that this unit is easy because it introduces two new controls that you've seen in many Windows programs, and it also builds upon arrays that you mastered in the previous unit. The check box and option button controls described here provide the user with choices of data values and options that the user can select. Unlike list and combo box controls, the check box and option button controls (shown in Figure 12.1's Toolbox window) are perfect controls for offering the user a limited number of choices.

Figure 12.1. The check box and option button controls.

Option Buttons Offer Choices

Concept: The option button control gives the user the ability to select one item from a list of several items that you display in a series of option button choices. Visual Basic keeps the user from selecting more than one option button at a time. The option button's events offer several ways for you to manage the option button selections.

List boxes and combo boxes are perfect controls for displaying scrolling lists of items from which the user can select and, in the case of combo boxes, add to. Unlike list and combo boxes, option buttons are good to use when you must offer the user a list of fixed choices that your program knows ahead of time.

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Tip: Think of option buttons as a multiple-choice selection from which the user can choose one item.

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Option buttons are sometimes called radio buttons. Perhaps you're old enough to remember pre-digital car radios that had five or six buttons sticking out with preset statements assigned to each button. At any one time, you could depress one button because the radio could play only one station at a time. When you pressed a button, any other button pressed inward immediately clicked out. The buttons were designed so that only one button at a time could be chosen.

Take the time to load CONTROLS.MAK and press the Next control command button until you see the option buttons shown in Figure 12.2. Try to click more than one option button and you'll see that Visual Basic keeps you from doing so.

Figure 12.2. You may select only one option button at a time.

Table 12.1 lists the property settings for the option button controls that you can set from within the Property window when you place option buttons on the form. There are several properties that you've seen before on other kinds of controls.

Table 12.2 contains a list of the option button's events that trigger event procedures you can write. Generally, the Click event procedure is the most commonly used so that an application can perform a specific action when the user selects a particular option button.

Stop and Type: Load and run this book's project named TRANSL.MAK. Listing 12.1 contains the code for the project's event procedures. The program allows the user to choose the target language into which "Good Morning" is translated. There is room on the form for only one translation, so the option buttons ensure that the user can select one translation at most.

Review: The option button controls enable you to add choices to the form. The user will be allowed to select from at most one choice by clicking (or tabbing to change the focus and pressing Enter) the option button of the desired option. By adding code to the option buttons' Click event procedures, you can respond to the user's choice.

Listing 12.1. The Form_Load() and four option button Click() procedures.

1: Sub 
Form_Load ()

2: ' Make sure that all option buttons are

3: ' False when first displaying the form

4: optFre.Value = 0

5: optIta.Value = 0

6: optSpa.Value = 0

7: optPig.Value = 0

8: End Sub

9:

10: Sub cmdExit_Click ()

11: End

12: End Sub

13:


14: Sub optFre_Click ()

15: ' Send the French message

16: lblTrans.Caption = "Bonjour"

17: End Sub

18:

19: Sub optIta_Click ()

20: ' Send the Italian message

21: lblTrans.Caption = "Buon giorno"

22: End Sub

23:

24: Sub 
optPig_Click ()

25: ' Send the Pig latin message

26: lblTrans.Caption = "oodGa ayDa"

27: End Sub

28:

29: Sub optSpa_Click ()

30: ' Send the Spanish message

31: lblTrans.Caption = "Buenos dìas"

32: End Sub

Output: Figure 12.3 shows the TRANSL.MAK screen just after the user selects the Italian option button. The Italian translation appears in the shaded label at the bottom of the screen.

Figure 12.3. The user wants to parla Italiano bene!

Analysis: Listing 12.1 looks a little different from the other listings that you've seen so far in this book. The listing contains more than one event procedure. As you've gathered by now, a Visual Basic program consists of lots of event procedures and possibly a (general) procedure. In Lesson 8, you'll learn about other kinds of procedures that a Visual Basic program may contain.

Although the default Value property for all option buttons is 0, meaning unselected, Visual Basic automatically selects an option button (the one with the lowest TabIndex property value) when loading the application. Therefore, lines 4 through 7 in Listing 12.1 set all four option button Value properties to 0 upon loading the form so that there is no option button set until the user selects one. (The four option buttons are named optFre, optIta, optPig, and optSpa.)

Lines 10 through 12 provide the familiar Exit command button event procedure that terminates the program when the user presses the Exit button.

Lines 14 through 32 complete the code with the four option button Click event procedures. The user triggers one of the four procedures by selecting one of the four option buttons. The shaded translation label at the bottom of the screen that will hold the translation is named lblTrans. The four option button Click event procedures change the Caption property of the lblTrans object to the appropriate translation that matches the option button's caption.

Check Boxes Offer More Choices

Concept: The check box control works a lot like the option button. You'll place several check boxes on a form; each check box represents a user-selected choice. Unlike option buttons, the user can select more than one check box item at a time.

Figure 12.4 contains the check box controls found in this book's CONTROLS.MAK application. If you load and run the program, the check boxes are the fourth set of controls on which you'll click. As you can see from Figure 12.4, when the user selects a check box, the check box is marked with an X, indicating a true selection. Two of the three check boxes are selected in Figure 12.4.

Figure 12.4. The check box controls allow for multiple selections.

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Note: Although the check box controls in Figure 12.4 don't contain access keystrokes, you can add access keystroke selection to check boxes just as you can for option button controls.

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Table 12.3 contains the property values available for check box controls. Most of the properties are equivalent to the option button properties.

Table 12.4 contains the events available for check box controls. As with option buttons, the Click event is generally the most commonly coded event procedure.

Stop and Type: Load and run this book's project named CHECK.MAK. Listing 12.2 contains the code for the project's event procedures. The program allows the user to choose from one to four special formatting options for the poem inside the boxed label. The poem can accept any or all four formatting options, so the check box controls enable the user to select one or more of the formatting options.

Review: The check box controls allow more than one selection from the user at a time, unlike the option button controls, which allow only a single option to be selected at a time.

Listing 12.2. The code for the CHECK.MAK project.

1: Sub Form_Load ()

2: ' Fill the label with a poem.

3: ' The poem will display initially

4: ' using the default label properties.

5: 
Dim Newline As String

6: ' The newline sends a carriage return and

7: ' line feed sequence to the poem so that

8: ' the poem can appear as a multiple-line

9: ' poem.

10: Newline = Chr$(13) + Chr$(10)

11: ' Fill the label with the poem

12: ' and 
concatenate the newline characters

13: lblPoem = "Visual Basic is the best."

14: lblPoem = lblPoem & Newline

15: lblPoem = lblPoem & "It's much better than the rest."

16: lblPoem = lblPoem & Newline

17: lblPoem = 
lblPoem & "If you ever hear differently,"

18: lblPoem = lblPoem & Newline

19: lblPoem = lblPoem & "Give them major misery!"

20: End Sub

21:

22: Sub chkBack_Click ()

23: ' Set the poem label's background to Red or white


24: If (lblPoem.BackColor = RED) Then

25: lblPoem.BackColor = WHITE ' Default

26: Else

27: lblPoem.BackColor = RED

28: End If

29: End Sub

30:

31: Sub chkFore_Click ()

32: ' Set the poem label's foreground to Green or Black

33: If 
(lblPoem.ForeColor = GREEN) Then

34: lblPoem.ForeColor = BLACK ' Default

35: Else

36: lblPoem.ForeColor = GREEN

37: End If

38: End Sub

39:

40: Sub chkItal_Click ()

41: ' Set the poem label's caption to italicize or not

42: If (lblPoem.FontItalic = 
True) Then

43: lblPoem.FontItalic = False ' Default

44: Else

45: lblPoem.FontItalic = True

46: End If

47: End Sub

48:

49: Sub chkUnd_Click ()

50: ' Set the poem label's caption to underline or not

51: If (lblPoem.FontUnderline = True) Then

52: 
lblPoem.FontUnderline = False ' Default

53: Else

54: lblPoem.FontUnderline = True

55: End If

56: End Sub

57:

58: Sub cmdExit_Click ()

59: End

60: End Sub

[ic:output]Figure 12.5 contains a figure that shows the poem when the user selects two of the check box options.

Figure 12.5. Selecting two check boxes at the same time.

Analysis: Lines 1 through 20 contain the longest Form_Load() event procedure that you've seen in this book. The purpose of the procedure is to initialize the label control with the multiline poem. There is no MultiLine property for labels, so you have to trick Visual Basic into displaying multiple lines inside the label.

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Definition: A control character produces an action, not a text character.

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The Chr$() function (called the character string function or, sometimes, the character function) accepts a number inside its parentheses. The number must come from the ASCII table (Appendix A). Visual Basic converts that number to its ASCII character equivalent. ASCII number 13 is the carriage return character and is a special control character that sends the cursor to the beginning of the line, which, in the case of a label, is the beginning column in the label. ASCII number 10 is the line feed character that sends the cursor to the next line on the screen. The effect of the concatenated ASCII value of 13 and 10 (line 10) is that a special double control character is created that, when displayed in a label, sends the cursor to the beginning of the label's next line.

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Note: The poem label's Alignment property is set to 2-Center, so the lines inside the label always display as centered within the label's border.

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Lines 13 through 19 then build the multiline poem by concatenating one line and the newline combination string variable to the label's Caption property.

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Note: But wait! Lines 13 through 19 don't even mention the Caption property! It appears that the poem's text is being sent to the label itself and not to any property. It turns out that each control has a default property that, unless you specify a different property name, acts as the default property. Therefore, Visual Basic assigns all of the poem's lines to the Caption property in lines 13 through 19 because the Caption property is the default property for labels.

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Lines 22 through 56 contain the four check box Click event procedures that set or reset each of the four poem properties described by the check box. The If-Else checks first to see whether the poem's property is set to the checked value. If so, the true part of the If sets the property back to its default state. If the property already contains the default value, the Else sets the property to the new state.

As always, the application contains an Exit command button event procedure in lines 58 through 60 that terminate the program at the user's request.

Multiple Sets of Option Buttons

Concept: Although the user can select only one option button from all the option buttons on the form, there is a way to place multiple sets of option buttons on a form inside frames. The user can select only one option button within any frame at a time.

Figure 12.6 shows where the frame control resides on the Toolbox window. The frame control is a holder of other controls. By placing more than one frame on a form, you can group more than one set of option buttons on the form together.

Figure 12.6. The location of the frame control.

When you want to place several sets of options buttons on a form, be sure to place more than one frame on the form first. The frames must be large enough to hold as many option buttons as each group requires.

Be careful about placing option buttons when you want to frame them within frame controls. You must draw the option buttons inside the frame. You can't create the option buttons elsewhere and move them into the frame. For most applications, you can double-click controls to place them in the middle of the form, and then drag the controls to their final location and resize them. When placing option buttons inside frames, you must click (not double-click) the option button control on the Toolbox window and then draw the option button by clicking the mouse inside the frame and dragging the mouse until you've approximated the option button's size. When you release the mouse button, Visual Basic will draw the option button in the size you drew it.

Stop and Type: Load and run this book's project named OPTIONS.MAK. Listing 12.3 contains the code for the project's event procedures. The program is similar to the CHECK.MAK application that you saw in the previous section. Framed groups of option buttons turn selected poem formatting properties on or off.

Review: The frame enables you to group option button controls together. Be sure to place the frame before drawing option button controls inside the frame.

Listing 12.3. The code for the framed option buttons.

1: Sub Form_Load ()

2: ' Fill the label with a poem.

3: ' The poem will display initially

4: ' using the default label properties.

5: Dim Newline As String

6: 
' The newline sends a carriage return and

7: ' line feed sequence to the poem so that

8: ' the poem can appear as a multiple-line

9: ' poem.

10: Newline = Chr$(13) + Chr$(10)

11: ' Fill the label with the poem

12: ' and concatenate the newline 
characters

13: lblPoem = "Visual Basic is the best."

14: lblPoem = lblPoem & Newline

15: lblPoem = lblPoem & "It's much better than the rest."

16: lblPoem = lblPoem & Newline

17: lblPoem = lblPoem & "If you 
ever hear differently,"

18: lblPoem = lblPoem & Newline

19: lblPoem = lblPoem & "Give them major misery!"

20: End Sub

21:

22: Sub optGreen_Click ()

23: lblPoem.BackColor = GREEN

24: End Sub

25:

26: Sub optItal_Click ()

27: 
lblPoem.FontItalic = True

28: End Sub

29:

30: Sub optNoItal_Click ()

31: lblPoem.FontItalic = False

32: End Sub

33:

34: Sub optNoUnd_Click ()

35: lblPoem.FontUnderline = False

36: End Sub

37:

38: Sub optRed_Click ()

39: lblPoem.BackColor = RED


40: End Sub

41:

42: Sub optUnd_Click ()

43: lblPoem.FontUnderline = True

44: End Sub

45:

46: Sub optWhite_Click ()

47: lblPoem.BackColor = WHITE

48: End Sub

49:

50: Sub cmdExit_Click ()

51: End

52: End Sub

Output: Figure 12.7 contains the OPTIONS.MAK application after the user selects an option in each of the three frames.

Figure 12.7. The framed option buttons allow for multiple settings.

Analysis: The difficult part of framed option controls is placing the option buttons inside the frames, and even that's not extremely difficult. After you draw the option buttons and the frames, the usual event procedures that you've been writing work for the controls.

Lines 22 through 48 contain the Click event procedures that set the poem's label formatting properties.

Control Arrays Simplify

Concept: By putting one or more similar controls inside a control array, you gain the advantage of writing a single event procedure that can handle more than one control on the form.

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Definition: A control array is a list of controls with the same name.

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When you place more than one control of the same control type on a form and assign the same Name property to those controls, you're creating a control array. As with variable arrays, a subscript that begins at 0 differentiates one control from another. The Index property of each control in the array contains that control's subscript location in the array. If you want to renumber the controls in the array to begin at 1, you can do so by changing the first zero-based control's Index value to 1.

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Note: Each control in a control array must be the same data type.

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If there were five text boxes in a control array named txtBoxes, each individual control would be named txtBoxes(0), txtBoxes(1), txtBoxes(2), txtBoxes(3), and txtBoxes(4).

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[ic: Note]As soon as you place a control on the form that has the same name as an existing control, Visual Basic makes sure that you want to begin a control array by issuing the warning message box shown in Figure 12.8. The designers of Visual Basic knew that you may accidentally attempt to place two controls on the same form with the same name, and the message box makes sure of your intent to create a control array. If you select the No command button to the warning message box, Visual Basic returns the second control to a its default name.

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Figure 12.8. Visual Basic ensures that you want a control array.

Stop and Type: Load and run this book's project named CHECK2.MAK. Listing 12.4 contains the code for the project's chkAll_Click() event procedure. The program is similar to the CHECK.MAK application that you saw in the previous section, except that, instead of four separate check box event procedures, CHECK2.MAK contains a single check box control array named chkAll.

Review: By placing several controls in a control array, you can reference each control by its subscript rather than by a different name for each control. Rather than write several event procedures, you need to write only a single event procedure.

Listing 12.4. The code for control array's event procedure.

1: Sub chkAll_Click (Index As Integer)

2: ' A single Select Case

3: ' handles all check box formats

4: Select Case Index

5: Case 0:

6: ' Set the poem label's background to Red or white

7: If (lblPoem.BackColor = 
RED) Then

8: lblPoem.BackColor = WHITE ' Default

9: Else

10: lblPoem.BackColor = RED

11: End If

12: Case 1:

13: ' Set the poem label's foreground to Green or Black

14: If (lblPoem.ForeColor = GREEN) Then

15: lblPoem.ForeColor = BLACK ' Default

16: 
Else

17: lblPoem.ForeColor = GREEN

18: End If

19: Case 2:

20: ' Set the poem label's caption to italicize or not

21: If (lblPoem.FontItalic = True) Then

22: lblPoem.FontItalic = False ' Default

23: Else

24: lblPoem.FontItalic = True

25: End If


26: Case 3:

27: ' Set the poem label's caption to underline or not

28: If (lblPoem.FontUnderline = True) Then

29: lblPoem.FontUnderline = False ' Default

30: Else

31: lblPoem.FontUnderline = True

32: End If

33: End Select

34: End Sub

Analysis: The single Select Case statement handles all four check boxes. There is only one single check box Click() procedure in the entire application even though there are four check boxes. Each check box is named chkAll, so they all a control array of check boxes and there will be only one event procedure for each event that the programmer wants to program.

Therefore, whenever the user clicks any of the check boxes, the chkAll_Click() event procedure executes. How does the procedure know which check box triggered the event? Line 1, the event procedure's first line, gives you a good clue. Visual Basic sends the Index value of the check box that the user clicked to the event procedure. The parentheses is a mechanism that Visual Basic uses to collect values such as the index to the control array that triggered the event. You'll understand such parenthetical values in Lesson 8, but until then, be assured that after the chkAll_Click() procedure executes, an Index variable will contain the subscript of the check box in the control array that the user selected.

The Select Case is a consolidation of Listing 12.2's multiple check box Click() event procedures. As you can see, the control array saves time and memory because a single event procedure can now handle all the events in the control array.

Homework

General Knowledge

1. Which control offers a single choice from a multiple set of choices?
   
   
2. Which control is best for allowing the user to select from one or more options?
   
   
3. Why are option buttons sometimes called radio buttons?
   
   
4. What happens if the user selects an option button that's different from the option button currently selected?
   
   
5. True or false: You can write code ensuring that no option button is selected when the program first executes.
   
   
6. What does the Alignment property do for option buttons and check boxes?
   
   
7. What property determines whether an option button is selected?
   
   
8. What property determines whether a check box is selected?
   
   
9. True or false: One or more Value properties can be set for option buttons on a form (assume that the option buttons aren't placed in frames).
   
   
10. True or false: One or more Value properties can be set for option buttons on a form (assume that the option buttons are placed in frames).
    
    
11. What is a frame?
    
    
12. True or false: You can place one frame at the most on a form at any one time.
    
    
13. What is a control character?
    
    
14. Describe how to initialize a label control with multiline text.
    
    
15. What does the Chr$() function do?
    
    
16. What is a control array?
    
    
17. If a control array contains seven controls, how many names do the controls have?
    
    
18. How do you distinguish between values in a control array?
    
    
19. What is the default starting subscript for control arrays?
    
    
20. How many event procedures do you have to write for a control array that contains eight controls?
    
    
21. What property holds a control array's subscript number?
    
    
22. How does Visual Basic make sure that you want to create a control array?
    
    

Write Code That...

1. Write the opening line of an DblClick event procedure for a command button control array named cmdAll.
   
   

Find the Bug

1. Opal is trying her hand at frames and option buttons. First, Opal places three frames on her form. Then, Opal double-clicks the option button control on the Toolbox window nine times and moves each control to its appropriate frame. Opal doesn't seem to be able to select more than one option button at a time on the entire form, even though the three sets of option buttons appear on different frames. What is Opal doing wrong?
   
   

Extra Credit

1. What character does the following assignment statement place in the string variable named MyGrade?
   MyGrade = Chr$(65)
   
   

Create a form that contains ten option buttons, two sets of five in two frames. Put the ten option buttons inside two control arrays. Label each option button One, Two, Three, Four, and Five. Write two Click event procedures, one for each option button control array, that beep the PC's speaker once for whatever option buttons are selected at that time. In other words, if the user clicks the left frame's Three option button, and the right frame already has the value Two selected, you'll click the speaker five times.