MFC Dialog: How to disable/change the behaviour of the <...> key in a dialog?

[Sonu Kapoor]

Q: How to disable/change the behaviour of the <...> key in a dialog?

A: There are several ways of doing it:

• The easiest way is to simply open the resource editor and set the 'Default button' property of the button which should act as the default one.
  
  
  
• The correct way of diasabling the <Enter> key in MFC is presented in Paul DiLascias' MSDN C++ Q/A Article Enabling Menus in MFC Apps, Changing the Behavior of Enter with DLGKEYS Sample App.. It boils down to processing the 'DM_GETDEFID' message to return 'DC_HASDEFID' in the high word:
  
  

  BEGIN_MESSAGE_MAP(CMyDialog, CDialog)
    ON_MESSAGE(DM_GETDEFID, OnGetDefID)
    //...
  END_MESSAGE_MAP()
  
  LRESULT CMyDialog::OnGetDefID(WPARAM wp, LPARAM lp) 
  {
    return MAKELONG(0,DC_HASDEFID); 
  }

  The article also discusses how to change the behaviour of <Enter> and other keys, providing a sample application with source code. Please refer to the article for details.
  
  
  
• Another workaround can be achieved by overriding 'OnOK()':
  
  

  void CYourDialog::OnOK(void)
  {
    CWnd* pWnd = GetFocus();
    if(GetDlgItem(IDOK) == pWnd)
    {
      CDialog::OnOK();
      return;
    }
    
    // Enter key was hit -> do whatever you want
  }

  This solution is a quick-fix, because it lacks on generality.
  
  
  
• Another 'hack' that seems to be very popular (but not recommendable) is overriding 'PreTranslateMessage()':
  
  

  BOOL CYourDialog::PreTranslateMessage(MSG* pMsg)
  {
    // ENTER key
    if((pMsg->message == WM_KEYDOWN) && 
       (pMsg->wParam == VK_RETURN))
    {
      // Enter key was hit -> do whatever you want
      return TRUE;
    }
  
    return CDialog::PreTranslateMessage(pMsg);
  }

  This is a 'hack' because it breaks the modularity of MFC. If you want to change the behaviour of more keys but just <Enter> you will end up with a labyrinth of 'if' statements in the overriden 'PreTranslateMessage()' function. This is ugly, hard to read, hard to maintain and error prone. The MFC way of doing it is presented in detail in DiLascias' Article.

For further information on the whole topic, take also a look at the article 'Processing Keyboard Messages ' written by Sam Hobbs.