Why doesn't OnKeyDown catch key events in a dialog-based MFC project?

Question

I just create a dialog-based project in MFC (VS2008) and add OnKeyDown event to the dialog. When I run the project and press the keys on the keyboard, nothing happens. But, if I remove all the controls from the dialog and rerun the project it works. What should I do to get key events even when I have controls on the dialog?

Here's a piece of code:

void CgDlg::OnKeyDown(UINT nChar, UINT nRepCnt, UINT nFlags)
{
    // TODO: Add your message handler code here and/or call default
    AfxMessageBox(L"Key down!");
    CDialog::OnKeyDown(nChar, nRepCnt, nFlags);
}

score 23 · Accepted Answer · edited Jan 15 '11 at 13:05

When a dialog has controls on it, the dialog itself never gets the focus. It's stolen by the child controls. When you press a button, a WM_KEYDOWN message is sent to the control with focus so your CgDlg::OnKeyDown is never called. Override the dialog's PreTranslateMessage function if you want dialog to handle the WM_KEYDOWN message:

BOOL CgDlg::PreTranslateMessage(MSG* pMsg)
{
   if(pMsg->message == WM_KEYDOWN   )  
   {
      if(pMsg->wParam == VK_DOWN)
      {
         ...
      }
      else if(pMsg->wParam == ...)
      {
         ...                      
      }
      ...
      else
      {
         ...                   
      }
   }

   return CDialog::PreTranslateMessage(pMsg);  
}

Also see this article on CodeProject: http://www.codeproject.com/KB/dialog/pretransdialog01.aspx

I added a `CMFCPropertyGridCtrl` in a dialog, and its `OnKeyDown` method is not being called.. — manatttta, May 28 '15 at 17:06

score 0 · Answer 2 · answered Sep 23 '11 at 16:38

Many of my CDialog apps use OnKeyDown(). As long you only want to receive key presses and draw on the screen (as in make a game), delete the default buttons and static text (the CDialog must be empty) and OnKeyDown() will start working. Once controls are placed on the CDialog, OnKeyDown() will no longer be called.

Why doesn't OnKeyDown catch key events in a dialog-based MFC project?

2 Answers2

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