How to prevent an MFC dialog from handling the enter and escape keys and not passing it on.

Question

Hi, we have a C++ application that hosts a flex application in a MFC dialog. Everything works fine, all button pushes etc are passed directly on to flex with no problem at all, except the enter and escape keys, which immediately closes the dialog.

We can trap the enter key, by implementing PreTranslateMessage() or OnOK() and impede the window closing behavior, but we still have the problem of passing these enter key pushes on to the hosted flex app further.

There is no "default" button on the form or anything like that, perhaps MFC is linking the enter key to the close button in the title bar behind the scenes or something.

Does anyone have any ideas how we can stop MFC from treating the enter key from being a special case.

Thanks a lot for any hints.

Edit: Here is PreTranslateMessage() that mmonem requested.

BOOL CFlexDialog::PreTranslateMessage(MSG* pMsg)
{
  if ((pMsg->message == WM_KEYDOWN))
  {
    if (pMsg->wParam == VK_RETURN)
    {
      m_ctrlFlex->OnReturnKeyPressed();
      return TRUE;
    }
  }
  return __super::PreTranslateMessage(pMsg);
}

But it is not a suitable solution, calling a method in the flex app like that, as it makes life too difficult for the flex developer, it means he must write a special version implementing the return key behavior for every control.

We just want MFC to treat the return and escape keys like every other key.

Answer 1

MFC command buttons can respond to events even if they do not have the focus.

Have you tried trapping the OnClicked event and OnOk to return nothing?

Example: trap OnClick...

   void CMyDialog::OnClickedMyOK()
   {
      CDialog::OnOK();
   }

Then do a no-op in the OnOk()

void CMyDialog::OnOK()
{
}

This should stop the enter key from being processed.

Answer 2

Another approach is "Windows Subclassing." That is, sending messages from one Window Procedure, that is a WindProc() to another WndProc(). This may provide a way without direct intervention. (This is not C++ subclassing.)

Here's a way with MFC Subclassing Edit: Provided a better link.

Search for "Windows / MFC Subclassing" if more info needed.

The flex control/window has a WndProc and your window certainly has a WndProc, Windows Subclassing should work.

---

New Edit: Here is perhaps a better link for subclassing an ActiveX control.

ActiveX Controls: Subclassing a Windows Control

Subclassing Windows Forms Controls - More .Net-centric.

Notice: In MFC you should see these functions.

CWnd::SubclassDlgItem

CWnd::SubclassWindow

CDialog inherits from CWnd so you will see those two functions as "dialog" functions as well. They are key to making this work. If the flash window is a true window, use SubclassWindow. If it's a control use SubclassDlgItem.

And finally, if nothing else works. A product/library that will hopefully make it easy. EasyHook looks like a product here. EasyHook at CodeProject, you can get all the source code.

Answer 3

Remove OnOK() and OnCancel(); PreTransateMessage is enough after considering VK_ESCAPE.

Why don't you use:

m_ctrlFlex->SendMessage(WM_KEYDOWN, VK_RETURN, 0)

instead of

m_ctrlFlex->OnReturnKeyPressed();

in your implementation of PreTranslateMessage ?

Answer 4

If you are having issues handling tabs & enter keys I would recommend you look into using a window instead of a dialog. The dialog adds modal ( if you are using modal ), tabbing & default button handling. If you don't need/want those features, or if they are getting in your way, then don't use a dialog.

If I understand what you are doing, then you want flex to handle tabbing, enter key, and all sorts of other messages. Get the dialog code out of the way. If you still want modal style, then you may have to handle the enable/disabling of parent windows - thats all that windows does when you open a modal dialog.