How to prevent MFC dialog closing on Enter and Escape keys?

c++ mfc
Laxman Sahni picture Laxman Sahni · Jul 24, 2013 · Viewed 26.8k times · Source

I know one method of preventing an MFC dialog from closing when the Enter or Esc keys are pressed, but I'd like to know more details of the process and all the common alternative methods for doing so.

Thanks in advance for any help.

Answer

rodrigo picture rodrigo · Jul 24, 2013

When the user presses Enter key in a dialog two things can happen:

  1. The dialog has a default control (see CDialog::SetDefID()). Then a WM_COMMAND with the ID of this control is sent to the dialog.
  2. The dialog does not have a default control. Then WM_COMMAND with ID = IDOK is sent to the dialog.

With the first option, it may happen that the default control has a ID equal to IDOK. Then the results will be the same that in the second option.

By default, class CDialog has a handler for the WM_COMMAND(IDOK) that is to call to CDialog::OnOk(), that is a virtual function, and by default it calls EndDialog(IDOK) that closes the dialog.

So, if you want to avoid the dialog being closed, do one of the following.

  1. Set the default control to other than IDOK.
  2. Set a handler to the WM_COMMAND(IDOK) that does not call EndDialog().
  3. Override CDialog::OnOk() and do not call the base implementation.

About IDCANCEL, it is similar but there is not equivalent SetDefID() and the ESC key is hardcoded. So to avoid the dialog being closed:

  1. Set a handler to the WM_COMMAND(IDCANCEL) that does not call EndDialog().
  2. Override CDialog::OnCancel() and do not call the base implementation.

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