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</center></div><font FACE="Times New Roman" SIZE="3"><b><p ALIGN="CENTER"></b></font><font color="#3973DE" FACE="Times New Roman" size="4">4.2</font><font color="#3973DE" size="4">工具条的编程技术</font><font FACE="Times New Roman" size="4"></p>
<p ALIGN="CENTER"></font><font SIZE="3"> </font><font FACE="Times New Roman" SIZE="3"></p>
<p></font><font SIZE="3">本节将讨论一些与工具条有关的编程技术，主要包括命令处理、命令更新、按钮风格和工具条的隐藏</font><font FACE="Times New Roman" SIZE="3">/</font><font SIZE="3">显示等技术。</font><b><font FACE="Times New Roman" SIZE="3"></p>
<p></font></b><font color="#3973DE" FACE="Times New Roman" SIZE="3">4.2.1</font><font SIZE="3" color="#3973DE">命令处理</font><font FACE="Times New Roman" SIZE="3"></p>
<p></font><font SIZE="3">要使菜单和工具条执行命令，光为它们指定命令</font><font FACE="Times New Roman" SIZE="3">ID</font><font SIZE="3">是不行的，必须为每个命令</font><font FACE="Times New Roman" SIZE="3">ID</font><font SIZE="3">定义命令处理函数。如果不为命令定义命令处理函数或下面将要提到的命令更新处理函数，则框架将自动使该命令对应的菜单项和按钮禁止（灰化），这就是</font><font FACE="Times New Roman" SIZE="3">4.1</font><font SIZE="3">节中的工具条按钮和菜单项灰化的原因。</font><font FACE="Times New Roman" SIZE="3"></p>
<p></font><font SIZE="3">利用</font><font FACE="Times New Roman" SIZE="3">ClassWizard</font><font SIZE="3">可以很方便地加入命令处理函数，请读者按以下步骤操作：</p>
<blockquote>
<blockquote>
<p>按</font><font FACE="Times New Roman" SIZE="3">Ctrl+W</font><font SIZE="3">键进入</font><font FACE="Times New Roman" SIZE="3">ClassWizard</font><font SIZE="3">。</p>
<p align="center"><img src="T4_6.gif" alt="T4_6.tif (317964 bytes)" WIDTH="515" HEIGHT="387"></p>
<p align="center">图<font FACE="Times New Roman" SIZE="3">4.6 ClassWizard</font>对话框</p>
<p>如图</font><font FACE="Times New Roman" SIZE="3">4.6</font><font SIZE="3">所示，在</font><font FACE="Times New Roman" SIZE="3">Class name</font><font SIZE="3">栏中选择</font><font FACE="Times New Roman" SIZE="3">CMainFrame</font><font SIZE="3">，在</font><font FACE="Times New Roman" SIZE="3">Object IDs</font><font SIZE="3">栏中选择</font><font FACE="Times New Roman" SIZE="3">ID_RECORD_START</font><font SIZE="3">，在</font><font FACE="Times New Roman" SIZE="3">Messages</font><font SIZE="3">栏中双击</font><font FACE="Times New Roman" SIZE="3">COMMAND</font><font SIZE="3">项，则</font><font FACE="Times New Roman" SIZE="3">ClassWizard</font><font SIZE="3">会弹出一个对话框询问命令处理函数的名字，使用其提供的函数名即可。按</font><font FACE="Times New Roman" SIZE="3">OK</font><font SIZE="3">按钮后，函数</font><font FACE="Times New Roman" SIZE="3">OnRecordStart</font><font SIZE="3">就被加入到了</font><font FACE="Times New Roman" SIZE="3">Member functions</font><font SIZE="3">栏中。</p>
<p>仿照第</font><font FACE="Times New Roman" SIZE="3">2</font><font SIZE="3">步，为</font><font FACE="Times New Roman" SIZE="3">ID_RECORD_STOP</font><font SIZE="3">定义一个命令处理函数。</p>
<p>按</font><font FACE="Times New Roman" SIZE="3">OK</font><font SIZE="3">按钮关闭</font><font FACE="Times New Roman" SIZE="3">ClassWizard</font><font SIZE="3">对话框。这时读者会发现</font><font FACE="Times New Roman" SIZE="3">CMainFrame</font><font SIZE="3">类多了两个成员函数，</font><font FACE="Times New Roman" SIZE="3">OnRecordStart</font><font SIZE="3">和</font><font FACE="Times New Roman" SIZE="3">OnRecordStop</font><font SIZE="3">。</p>
<p>现在要在这两个命令处理函数中插入相应的源代码以实现其功能。当然，这里不会真的实现开始录音和停止录音的功能。我们只是让这两个函数发出一个声音，象征性地表示功能的执行，具体代码如清单</font><font FACE="Times New Roman" SIZE="3">4.2</font><font SIZE="3">所示。</p>
</font>
</blockquote>
</blockquote>
<p><font SIZE="3"> </p>
<p>清单</font><font FACE="Times New Roman" SIZE="3">4.2<b> OnRecordStart</font><font SIZE="3">和</font><font FACE="Times New Roman" SIZE="3">OnRecordStop</font><font SIZE="3">函数</font></b><font FACE="Times New Roman" SIZE="3"></p>
<p>void CMainFrame::OnRecordStart() </p>
<p>{</p>
<p>// TODO: Add your command handler code here</p>
<p></font><b><font SIZE="3"> </font><font FACE="Times New Roman" SIZE="3"></p>
<p>MessageBeep((UINT)(-1));</b></p>
<p>}</p>
<p>void CMainFrame::OnRecordStop() </p>
<p>{</p>
<p>// TODO: Add your command handler code here</p>
<p></font><b><font SIZE="3"> </font><font FACE="Times New Roman" SIZE="3"></p>
<p>MessageBeep((UINT)(-1));</b></p>
<p>}</p>
<p></font><font SIZE="3"> </font><font FACE="Times New Roman" SIZE="3"></p>
<p></font><font SIZE="3">编译并运行</font><font FACE="Times New Roman" SIZE="3">Record</font><font SIZE="3">，可以看到</font><font FACE="Times New Roman" SIZE="3">Start</font><font SIZE="3">和</font><font FACE="Times New Roman" SIZE="3">Stop</font><font SIZE="3">命令已经可以执行了。</font><font FACE="Times New Roman" SIZE="3"><b></p>
<p></b></font><font color="#3973DE" FACE="Times New Roman" SIZE="3">4.2.2</font><font SIZE="3" color="#3973DE">命令更新</font><font FACE="Times New Roman" SIZE="3"></p>
<p></font><font SIZE="3">虽然</font><font FACE="Times New Roman" SIZE="3">Start</font><font SIZE="3">和</font><font FACE="Times New Roman" SIZE="3">Stop</font><font SIZE="3">命令可以执行了，但是还有一个不足之处。在没有开始录音之前，</font><font FACE="Times New Roman" SIZE="3">Stop</font><font SIZE="3">命令应该是禁止的，也即对应的菜单项和按钮应是禁止的，这是因为此时没有必要执行该命令。录音开始后，</font><font FACE="Times New Roman" SIZE="3">Stop</font><font SIZE="3">命令应该允许，而</font><font FACE="Times New Roman" SIZE="3">Start</font><font SIZE="3">命令则应变为禁止。我们可以利用</font><font FACE="Times New Roman" SIZE="3">MFC</font><font SIZE="3">的命令更新机制实现此逻辑功能。</font><font FACE="Times New Roman" SIZE="3"></p>
<p></font><font SIZE="3">在菜单下拉之前，或在工具条按钮处在空闲循环期间，</font><font FACE="Times New Roman" SIZE="3">MFC</font><font SIZE="3">会发一个更新命令，这将导致命令更新处理函数的调用。命令更新处理函数可以根据情况，使用户接口对象（主要指菜单项和工具条按钮）允许或禁止。定义命令更新处理函数的方法如下：</p>
<blockquote>
<blockquote>
<p>按</font><font FACE="Times New Roman" SIZE="3">Ctrl+W</font><font SIZE="3">键进入</font><font FACE="Times New Roman" SIZE="3">ClassWizard</font><font SIZE="3">。</p>
<p align="center"><img src="T4_7.gif" alt="T4_7.tif (317964 bytes)" WIDTH="518" HEIGHT="389"></p>
<p align="center">图<font FACE="Times New Roman" SIZE="3">4.7 ClassWizard</font>对话框</p>
<p ALIGN="JUSTIFY">如图</font><font FACE="Times New Roman" SIZE="3">4.7</font><font SIZE="3">所示，在</font><font FACE="Times New Roman" SIZE="3">Class name</font><font SIZE="3">栏中选择</font><font FACE="Times New Roman" SIZE="3">CMainFrame</font><font SIZE="3">，在</font><font FACE="Times New Roman" SIZE="3">Object IDs</font><font SIZE="3">栏中选择</font><font FACE="Times New Roman" SIZE="3">ID_RECORD_START</font><font SIZE="3">，在</font><font FACE="Times New Roman" SIZE="3">Messages</font><font SIZE="3">栏中双击</font><font FACE="Times New Roman" SIZE="3">UPDATE_COMMAND_UI</font><font SIZE="3">项，则</font><font FACE="Times New Roman" SIZE="3">ClassWizard</font><font SIZE="3">会弹出一个对话框询问命令更新处理函数的名字，使用其提供的函数名即可。按</font><font FACE="Times New Roman" SIZE="3">OK</font><font SIZE="3">按钮后，函数</font><font FACE="Times New Roman" SIZE="3">OnUpdateRecordStart</font><font SIZE="3">就被加入到了</font><font FACE="Times New Roman" SIZE="3">Member functions</font><font SIZE="3">栏中。</p>
<p>仿照步</font><font FACE="Times New Roman" SIZE="3">2</font><font SIZE="3">，为</font><font FACE="Times New Roman" SIZE="3">ID_RECORD_STOP</font><font SIZE="3">定义一个命令更新处理函数。</p>
<p>按</font><font FACE="Times New Roman" SIZE="3">OK</font><font SIZE="3">按钮关闭</font><font FACE="Times New Roman" SIZE="3">ClassWizard</font><font SIZE="3">对话框。这时读者会发现</font><font FACE="Times New Roman" SIZE="3">CMainFrame</font><font SIZE="3">类多了两个成员函数，</font><font FACE="Times New Roman" SIZE="3">OnUpdateRecordStart</font><font SIZE="3">和</font><font FACE="Times New Roman" SIZE="3">OnUpdateRecordStop</font><font SIZE="3">。</font></p>
</blockquote>
</blockquote>
<p><font SIZE="3"> </font><font FACE="Times New Roman" SIZE="3"></p>
<p></font><font SIZE="3">命令更新处理函数有一个参数是</font><font FACE="Times New Roman" SIZE="3">CCmdUI</font><font SIZE="3">类的指针，通过调用</font><font FACE="Times New Roman" SIZE="3">CCmdUI</font><font SIZE="3">类的成员函数</font><font FACE="Times New Roman" SIZE="3">Enable(TRUE)</font><font SIZE="3">或</font><font FACE="Times New Roman" SIZE="3">Enable(FALSE)</font><font SIZE="3">可以使用户接口对象允许或禁止。需要给</font><font FACE="Times New Roman" SIZE="3">CMainFrame</font><font SIZE="3">加一个布尔型成员变量以表明是否正在录音，这样命令更新处理函数可根据这个变量来决定用户接口对象的状态。请读者在</font><font FACE="Times New Roman" SIZE="3">CMainFrame</font><font SIZE="3">类内加入下面一行代码：</font><font FACE="Times New Roman" SIZE="3"><b></p>
<p>BOOL m_bWorking;</b></p>
<p></font><font SIZE="3">接下来请读者按清单</font><font FACE="Times New Roman" SIZE="3">4.3</font><font SIZE="3">进行修改。<b></p>
<p>清单</font><font FACE="Times New Roman" SIZE="3">4.3 </font><font SIZE="3">命令更新处理</font></b><font FACE="Times New Roman" SIZE="3"></p>
<p>CMainFrame::CMainFrame()</p>
<p>{</p>
<p>// TODO: add member initialization code here</p>
<p></font><b><font SIZE="3"> </font><font FACE="Times New Roman" SIZE="3"></p>
<p>m_bWorking=FALSE; </b></p>
<p>}</p>
<p>void CMainFrame::OnRecordStart() </p>
<p>{</p>
<p>// TODO: Add your command handler code here</p>
<p>MessageBeep((UINT)(-1));</p>
<p></font><b><font SIZE="3"> </font><font FACE="Times New Roman" SIZE="3"></p>
<p>m_bWorking=TRUE;</b></p>
<p>}</p>
<p>void CMainFrame::OnRecordStop() </p>
<p>{</p>
<p>// TODO: Add your command handler code here</p>
<p>MessageBeep((UINT)(-1));</p>
<p></font><b><font SIZE="3"> </font><font FACE="Times New Roman" SIZE="3"></p>
<p>m_bWorking=FALSE;</b></p>
<p>}</p>
<p>void CMainFrame::OnUpdateRecordStart(CCmdUI* pCmdUI) </p>
<p>{</p>
<p>// TODO: Add your command update UI handler code here</p>
<p></font><b><font SIZE="3"> </font><font FACE="Times New Roman" SIZE="3"></p>
<p>pCmdUI->Enable(!m_bWorking); </b></p>
<p>}</p>
<p>void CMainFrame::OnUpdateRecordStop(CCmdUI* pCmdUI) </p>
<p>{</p>
<p>// TODO: Add your command update UI handler code here</p>
<p></font><b><font SIZE="3"> </font><font FACE="Times New Roman" SIZE="3"></p>
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