How to prevent MFC dialog closing on Enter and Esc

问题:

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.

回答1:

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.

回答2:

There is an alternative to the previous answer, which is useful if you wish to still have an OK / Close button. If you override the PreTranslateMessage function, you can catch the use of VK_ESCAPE / VK_RETURN like so:

BOOL MyCtrl::PreTranslateMessage(MSG* pMsg)
{
    if( pMsg->message == WM_KEYDOWN )
    {
        if(pMsg->wParam == VK_RETURN || pMsg->wParam == VK_ESCAPE)
        {
            return TRUE;                // Do not process further
        }
    }

    return CWnd::PreTranslateMessage(pMsg);
}

回答3:

I simply override the OnOk event and instead of passing the message to the parent dialog, do nothing.
So it's basically simple as doing so:

void OnOk() override { /*CDialog::OnOK();*/ }

This should prevent the dialog from closing when pressing the return/enter key.