How to subclass CListBox and CEdit inside of CComboBox-优快云博客

本文链接：https://blog.youkuaiyun.com/skyremember/article/details/995158

本文介绍了一种简单的方法来子类化组合框内的编辑框和列表框控件。通过处理WM_CTLCOLOR消息，可以安全地获取这些子控件的句柄，并进行子类化操作。

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How to subclass CListBox and CEdit inside of CComboBox

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Article ID	:	174667
Last Review	:	September 1, 2005
Revision	:	4.0

This article was previously published under Q174667

SUMMARY

While it is simple to directly subclass a combo box control, it is not simple to subclass the edit or list box inside a combo box. The problem is that it is difficult to get the HWNDs of the child controls in a portable manner.

One safe way to subclass the internal edit and list box controls is to subclass them in the WM_CTLCOLORXXX messages. Because Win32 sends separate WM_CTLCOLOREDIT and WM_CTLCOLORLISTBOX messages, these messages are safe and easy ways to get the HWNDs of the child controls of the combo box.

Below is a CSuperComboBox class, which is an MFC implementation of this method. Because MFC routes all the WM_CTLCOLOR messages to OnCtlColor, the subclassing takes place there.

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MORE INFORMATION

Use ClassWizard to derive a class from CComboBox and add message handlers for WM_CTLCOLOR and WM_DESTROY. Then manually edit the header file to add the data members, m_edit and m_listbox. Finally, copy the code from the message handlers below:

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Sample code

   // SuperComboBox.h : header file
   class CSuperComboBox : public CComboBox
   {
   public:
      CEdit      m_edit;
      CListBox   m_listbox;
   protected:
      afx_msg HBRUSH OnCtlColor(CDC* pDC, CWnd* pWnd, UINT nCtlColor);
      afx_msg void OnDestroy();
   ...
   };

   // SuperComboBox.cpp : implementation file
   HBRUSH CSuperComboBox::OnCtlColor(CDC* pDC, CWnd* pWnd, UINT nCtlColor)
   {
      if (nCtlColor == CTLCOLOR_EDIT)
      {
         //[ASCII 160][ASCII 160][ASCII 160]Edit control
         if (m_edit.GetSafeHwnd() == NULL)
            m_edit.SubclassWindow(pWnd->GetSafeHwnd());
      }
      else if (nCtlColor == CTLCOLOR_LISTBOX)
      {
         //ListBox control
         if (m_listbox.GetSafeHwnd() == NULL)
            m_listbox.SubclassWindow(pWnd->GetSafeHwnd());
      }
      HBRUSH hbr = CComboBox::OnCtlColor(pDC, pWnd, nCtlColor);
      return hbr;
   }

   void CSuperComboBox::OnDestroy()
   {
      if (m_edit.GetSafeHwnd() != NULL)
         m_edit.UnsubclassWindow();
      if (m_listbox.GetSafeHwnd() != NULL)
         m_listbox.UnsubclassWindow();
      CComboBox::OnDestroy();
   }