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📁 vb实例,很好很好用的哦,处学者的天堂这是第四部分
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<title>第四章：按钮</title>
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        <td width="100%"><font size="3" color="#8000FF"><strong><em>第四章：按钮（2）</em></strong></font></td>
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        <td width="100%" style="background-color: rgb(232,255,254)">　<p ALIGN="JUSTIFY"><strong>上面举了一个比较简单的例子，下面的例子稍微复杂些：</strong></p>
        <p ALIGN="JUSTIFY"><strong>新建窗体，控件布局如图4－3所示，包括一个List控件，一个Text控件和两个按钮（Command1和Command2），（比较简单的程序我们都采用缺省名），对它们属性做如下修改：</strong></p>
        <p ALIGN="JUSTIFY"><img src="0403.gif" alt="04－03.gif (2583 字节)" WIDTH="320" HEIGHT="240"></p>
        <table BORDER="1" CELLSPACING="1" CELLPADDING="7" WIDTH="283">
          <tr>
            <td WIDTH="28%" VALIGN="TOP"><p ALIGN="JUSTIFY"><strong>List1 </strong></td>
            <td WIDTH="72%" VALIGN="TOP"><p ALIGN="JUSTIFY"><strong>Caption＝“请输入你的名字”</strong></td>
          </tr>
          <tr>
            <td WIDTH="28%" VALIGN="TOP"><p ALIGN="JUSTIFY"><strong>Text1 </strong></td>
            <td WIDTH="72%" VALIGN="TOP"><p ALIGN="JUSTIFY"><strong>Text＝“”（空字符串)</strong></td>
          </tr>
          <tr>
            <td WIDTH="28%" VALIGN="TOP"><p ALIGN="JUSTIFY"><strong>Button1 </strong></td>
            <td WIDTH="72%" VALIGN="TOP"><p ALIGN="JUSTIFY"><strong>Caption＝“复原”</strong></p>
            <p ALIGN="JUSTIFY"><strong>Enabled＝False</strong></td>
          </tr>
          <tr>
            <td WIDTH="28%" VALIGN="TOP"><p ALIGN="JUSTIFY"><strong>Button2</strong></td>
            <td WIDTH="72%" VALIGN="TOP"><p ALIGN="JUSTIFY"><strong>Caption=“清除”</strong></td>
          </tr>
        </table>
        <p ALIGN="JUSTIFY"><strong>把使用Button1的Enabled属性设为False（假），是使程序在初始时，无法单击Command1。按F5，运行程序，图4－4，复原按钮成为灰色，不可选。</strong></p>
        <p ALIGN="JUSTIFY"><img src="0404.gif" alt="04－04.gif (2517 字节)" WIDTH="320" HEIGHT="240"></p>
        <p ALIGN="JUSTIFY"><strong>当然现在程序还什么也不能做，下面我们在程序中添加代码：</strong></p>
        <p ALIGN="JUSTIFY"><strong>首先在General里声明全局变量：</strong></p>
        <p ALIGN="JUSTIFY"><strong><font color="#004080">Dim StoreString As String</font><font color="#008000"> '用来储存字符串</font></strong></p>
        <p ALIGN="JUSTIFY"><font color="#FF0000"><strong>※注意：为什么用全局变量？</strong></font></p>
        <p ALIGN="JUSTIFY"><strong>VB里每一个小过程都相当于一个程序，程序里的变量称为局部变量，是只能在程序内部使用的，而当程序调用结束后，由于从内存中被清除，所以变量储存的值也就消失了，这里的全局变量是用来在过程中传递字符串。</strong></p>
        <p ALIGN="JUSTIFY"><strong>接着填写以下代码：</strong></p>
        <p ALIGN="JUSTIFY"><font color="#004080"><strong>Private Sub Command1_Click()</strong></font></p>
        <blockquote>
          <p ALIGN="JUSTIFY"><font color="#004080"><strong>Text1.Text = StoreString<br>
          Command1.Enabled = False</strong></font></p>
        </blockquote>
        <p ALIGN="JUSTIFY"><font color="#004080"><strong>End Sub</strong></font></p>
        <p ALIGN="JUSTIFY">　</p>
        <p ALIGN="JUSTIFY"><font color="#004080"><strong>Private Sub Command2_Click()</strong></font></p>
        <blockquote>
          <p ALIGN="JUSTIFY"><strong><font color="#004080">StoreString = Text1.Text<br>
          Text1.Text = &quot;&quot; </font><font color="#008040">'清除</font><font color="#004080"><br>
          Command1.Enabled = True</font></strong></p>
        </blockquote>
        <p ALIGN="JUSTIFY"><font color="#004080"><strong>End Sub</strong></font></p>
        <p ALIGN="JUSTIFY"><strong>运行程序，如图4－5。按下“清除”，文本框被清除，按下“复原”，文本有被恢复，许多程序中的Undo/Redo就是利用这个原理实现的，现在知道为什么内存越多越好了吧。</strong></p>
        <p ALIGN="JUSTIFY"><img src="0405.gif" alt="04－05.gif (2637 字节)" WIDTH="320" HEIGHT="240"></p>
        <p ALIGN="JUSTIFY"><strong>我们在把程序修改一下，把Button2删除，Button1的Enabled属性改为True，Caption改为“清除”，填写代码：</strong></p>
        <p ALIGN="JUSTIFY"><font color="#004080"><strong>Private Sub Command1_Click()</strong></font></p>
        <blockquote>
          <p ALIGN="JUSTIFY"><font color="#004080"><strong>If Command1.Caption = &quot;清除&quot; 
          Then</strong></font></p>
          <blockquote>
            <p ALIGN="JUSTIFY"><strong><font color="#004080">StoreString = Text1.Text<br>
            Text1.Text = &quot;&quot; </font><font color="#008040">'清除</font><font color="#004080"><br>
            Command1.Caption = &quot;复原&quot;</font></strong></p>
          </blockquote>
          <p ALIGN="JUSTIFY"><font color="#004080"><strong>Else</strong></font></p>
          <blockquote>
            <p ALIGN="JUSTIFY"><font color="#004080"><strong>Text1.Text = StoreString<br>
            Command1.Caption = &quot;清除&quot;</strong></font></p>
          </blockquote>
          <p ALIGN="JUSTIFY"><font color="#004080"><strong>End If</strong></font></p>
        </blockquote>
        <p ALIGN="JUSTIFY"><font color="#004080"><strong>End Sub</strong></font></p>
        <p ALIGN="JUSTIFY"><strong>同样可以上面的功能，但是却少用了一个控件，控件使用少的程序启动会快些。</strong></td>
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