vel12.htm

来自「简单的说明如何使用VB,非常适合初学使用者,而且是用图表来解说的」· HTM 代码 · 共 2,319 行 · 第 1/4 页

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</FONT></PRE>

<P><FONT 
COLOR="#FF8000"><B><I>Output: </I></B></FONT>Figure 12.7 contains the OPTIONS.MAK application after the user selects an option in each of the three frames.

<BR>

<P><B> <A HREF="12vel07.gif">Figure 12.7. The framed option buttons allow for multiple 
settings.</A></B>

<BR>

<P><FONT COLOR="#FF8000"><B><I>Analysis: </I></B></FONT>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.

<BR>

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

<BR>

<BR>

<A NAME="E68E95"></A>

<H3 ALIGN=CENTER>


<CENTER>

<FONT SIZE=5 COLOR="#FF0000"><B>Control Arrays Simplify</B></FONT></CENTER></H3>

<BR>

<P><FONT COLOR="#FF8000"><B><I>Concept: </I></B></FONT>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.

<BR>

<BLOCKQUOTE>

<BLOCKQUOTE>

<HR ALIGN=CENTER>

<BR>

<NOTE><I>Definition: </I>A <I>control array</I> is a list of controls with the same name.</NOTE>

<BR>

<HR ALIGN=CENTER>


</BLOCKQUOTE></BLOCKQUOTE>

<P>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.

<BR>

<BLOCKQUOTE>

<BLOCKQUOTE>

<HR ALIGN=CENTER>

<BR>

<NOTE><B>Note: </B>Each control in a control array must be the same data type.</NOTE>

<BR>

<HR ALIGN=CENTER>

</BLOCKQUOTE></BLOCKQUOTE>

<P>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).

<BR>

<BLOCKQUOTE>

<BLOCKQUOTE>

<HR ALIGN=CENTER>

<BR>

<NOTE>[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.</NOTE>

<BR>

<HR ALIGN=CENTER>

</BLOCKQUOTE></BLOCKQUOTE>

<P><B> <A HREF="12vel08.gif">Figure 12.8. Visual Basic ensures that you want a control array.</A></B>

<BR>

<P><FONT COLOR="#FF8000"><B><I>Stop and Type: </I></B></FONT>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.

<BR>

<P><FONT COLOR="#FF8000"><B><I>Review: </I></B></FONT>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.

<BR>

<P>

<FONT COLOR="#000080"><B>Listing 12.4. The code for control array's event procedure.</B></FONT>


<BR>

<PRE>

<FONT COLOR="#000080">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</FONT></PRE>


<P><FONT COLOR="#FF8000"><B><I>Analysis: </I></B></FONT>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.

<BR>

<P>Therefore, whenever the user clicks <I>any</I> of the check boxes, the chkAll_Click() event 
procedure executes. How does the procedure know <I>which</I> 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.

<BR>

<P>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.

<BR>

<BR>

<A NAME="E68E96"></A>

<H3 ALIGN=CENTER>

<CENTER>

<FONT SIZE=5 COLOR="#FF0000"><B>Homework</B></FONT></CENTER></H3>


<BR>

<BR>

<A NAME="E69E81"></A>

<H4 ALIGN=CENTER>

<CENTER>

<FONT SIZE=4 COLOR="#FF0000"><B>General Knowledge</B></FONT></CENTER></H4>

<BR>

<OL>

<LI>Which control offers a single choice from a multiple set of choices?

<BR>

<BR>

<LI>Which control 
is best for allowing the user to select from one or more options?

<BR>

<BR>

<LI>Why are option buttons sometimes called <I>radio buttons</I>?

<BR>

<BR>

<LI>What happens if the user selects an option button that's different from the option button 
currently selected?

<BR>

<BR>

<LI>True or false: You can write code ensuring that no option button is selected when the program first executes.

<BR>

<BR>

<LI>What does the Alignment property do for option buttons and check boxes?

<BR>

<BR>


<LI>What property determines whether an option button is selected?

<BR>

<BR>

<LI>What property determines whether a check box is selected?

<BR>

<BR>

<LI>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).

<BR>

<BR>

<LI>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).

<BR>

<BR>

<LI>What is a frame?

<BR>

<BR>

<LI>True 
or false: You can place one frame at the most on a form at any one time.

<BR>

<BR>

<LI>What is a <I>control character?</I>

<BR>

<BR>

<LI>Describe how to initialize a label control with multiline text.

<BR>

<BR>

<LI>What does the Chr$() function 
do?

<BR>

<BR>

<LI>What is a <I>control array</I>?

<BR>

<BR>

<LI>If a control array contains seven controls, how many names do the controls have?

<BR>

<BR>

<LI>How do you distinguish between values in a control array?

<BR>

<BR>

<LI>What is the 
default starting subscript for control arrays?

<BR>

<BR>

<LI>How many event procedures do you have to write for a control array that contains eight controls?

<BR>

<BR>

<LI>What property holds a control array's subscript number?

<BR>

<BR>

<LI>How 
does Visual Basic make sure that you want to create a control array?

<BR>

<BR>

</OL>

<BR>

<A NAME="E69E82"></A>

<H4 ALIGN=CENTER>

<CENTER>

<FONT SIZE=4 COLOR="#FF0000"><B>Write Code That...</B></FONT></CENTER></H4>

<BR>

<OL>

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

<BR>

<BR>

</OL>

<P><B>Find the Bug</B>

<OL>

<LI>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?

<BR>

<BR>

</OL>

<BR>

<A NAME="E69E83"></A>

<H4 ALIGN=CENTER>

<CENTER>

<FONT SIZE=4 COLOR="#FF0000"><B>Extra Credit</B></FONT></CENTER></H4>

<BR>

<OL>

<LI>What character does the 
following assignment statement place in the string variable named MyGrade?

<BR>MyGrade = Chr$(65)

<BR>

<BR>

</OL>

<P>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.

<P ALIGN=LEFT>

<A HREF="vel11.htm" TARGET="_self"><IMG SRC="purprev.gif" WIDTH = 32 HEIGHT = 32 BORDER = 0 ALT="Previous 
Page"></A>

<A HREF="#I0" TARGET="_self"><IMG SRC="purtop.gif" WIDTH = 32 HEIGHT = 32 BORDER = 0 ALT="Page Top"></A>

<A HREF="index.htm" TARGET="_self"><IMG SRC="purtoc.gif" WIDTH = 32 HEIGHT = 32 BORDER = 0 ALT="TOC"></A>

<A HREF="velp06.htm" 
TARGET="_self"><IMG SRC="purnext.gif" WIDTH = 32 HEIGHT = 32 BORDER = 0 ALT="Next Page"></A>


</BODY></HTML>