MFC Edit Control EN_KILLFOCUS issue

Question

I am using Visual Studio 2013 and making MFC Dialog based application. I am running into strange issue with Kill Focus of Edit Control.

Please see below:

==========================================================================

In my application, I have two Edit Controls on Dialog Box.

1st Edit Control -> IDC_EDIT_QUALITY1
2nd Edit Control -> IDC_EDIT_QUALITY2

I have handled both's EN_KILLFOCUS event to validate the value.

BEGIN_MESSAGE_MAP(CTestDlg, CDialog)
    ON_EN_KILLFOCUS(IDC_EDIT_QUALITY1, &CTestDlg::OnQuality1EditKillFocus)
    ON_EN_KILLFOCUS(IDC_EDIT_QUALITY2, &CTestDlg::OnQuality2EditKillFocus)
END_MESSAGE_MAP()

void CTestDlg::OnQuality1EditKillFocus()
{
    ValidateQualityParams(IDC_EDIT_QUALITY1);
}

void CTestDlg::OnQuality2EditKillFocus()
{
    ValidateQualityParams(IDC_EDIT_QUALITY2);
}

#define MIN_QUALITY_VALUE     1     
#define MAX_QUALITY_VALUE   100

void CTestDlg::ValidateQualityParams(int qualityParamID)
{
    CString strQuality1;
    if (IDC_EDIT_QUALITY1 == qualityParamID)
    {
        m_ctrlQuality1.GetWindowText(strQuality1);
        if ((_ttoi(strQuality1) < MIN_QUALITY_VALUE) || (_ttoi(strQuality1) > MAX_QUALITY_VALUE))
        {
            CString strMessage;
            strMessage.Format(_T("Quality1 value must be between %d to %d."), MIN_QUALITY_VALUE, MAX_QUALITY_VALUE);
            **AfxMessageBox(strMessage);**
            m_ctrlQuality1.SetSel(0, -1);
            m_ctrlQuality1.SetFocus();
            return;
        }
    }

    CString strQuality2;
    if (IDC_EDIT_QUALITY2 == qualityParamID)
    {
        m_ctrlQuality2.GetWindowText(strQuality2);
        if ((_ttoi(strQuality2) < MIN_QUALITY_VALUE) || (_ttoi(strQuality2) > MAX_QUALITY_VALUE))
        {
            CString strMessage;
            strMessage.Format(_T("Quality2 value must be between %d to %d."), MIN_QUALITY_VALUE, MAX_QUALITY_VALUE);
            AfxMessageBox(strMessage);
            m_ctrlQuality2.SetSel(0, -1);
            m_ctrlQuality2.SetFocus();
            return;
        }
    }
}

Now, the issue happens when, after changing the value in 1st Edit Control (IDC_EDIT_QUALITY1), say entering 0 in it and pressing TAB key, the flow goes as below:

• void CTestDlg::OnQuality1EditKillFocus() is called.
  
• It calls ValidateQualityParams(IDC_EDIT_QUALITY1)
  
• Inside ValidateQualityParams, it goes to if (IDC_EDIT_QUALITY1 == qualityParamID) condition.
  
• As the value I entered is less than MIN_QUALITY_VALUE, so it shows the Message by calling AfxMessageBox.
  - Now, even from the callstack of AfxMessageBox, it hits void CTestDlg::OnQuality2EditKillFocus() internally.

Although callstack of OnQuality1EditKillFocus is NOT finished yet, OnQuality2EditKillFocus gets called from the callstack of AfxMessageBox.

I don't understand the cause of this issue. Has anyone encountered such issue before?

In my resource.h, I have two distinct values for IDC_EDIT_QUALITY1 and IDC_EDIT_QUALITY2

 #define IDC_EDIT_QUALITY1               1018
 #define IDC_EDIT_QUALITY2               1020

Please help on this issue.

Answer 1

When you pressed TAB key, IDC_EDIT_QUALITY2 got focus. But because value entered was out of bound, the program called m_ctrlQuality1.SetFocus(), which in turn caused OnQuality2EditKillFocus() to get called. Add a member variable says m_bQuality1OutOfBound and set it to true right before calling m_ctrlQuality1.SetFocus(). In OnQuality2EditKillFocus(), when m_bQuality1OutOfBound is true, set it to false and don't call ValidateQualityParams(IDC_EDIT_QUALITY2).

Answer 2

I believe the EN_KILLFOCUS notification for the IDC_EDIT_QUALITY2 control you are receiving is caused not by the m_ctrlQuality1.SetFocus() call, but instead by the AfxMessageBox() call.

When you press the [Tab] key IDC_EDIT_QUALITY1 loses the focus, and IDC_EDIT_QUALITY2 gets the focus. Then you receive the EN_KILLFOCUS notification for IDC_EDIT_QUALITY1. You display the error-message, which causes the application to "yield" (start processing messages again), while the message-box is displayed. The m_ctrlQuality1.SetFocus() call won't take place before the AfxMessageBox() returns, ie before you close the message-box, and therefore the EN_KILLFOCUS notification for IDC_EDIT_QUALITY2 can't be the result of that call. I guess it's the result of displaying the message-box (IDC_EDIT_QUALITY2 has got the focus, but the message-box makes it lose it).

You may work around it by adding a memeber variable, as Staytuned123 suggested, but in a different setting: name it, say m_bKillFocusProcessing, and set it to TRUE while you are processing ANY EN_KILLFOCUS notification (AfxMessageBox() plus SetFocus()), and to FALSE when you are done processing it; if it's already TRUE exit without doing anything. That is, only one EN_KILLFOCUS notification may be processed at a time.

However, such a user-interface (displaying a message-box on exiting a field) is rather weird. And why reinvent the wheel and not instead use the DDX/DDV feature, which MFC already offers? You can define member variables associated with controls, and perform various checks, including range-check. Call UpdateData(TRUE) to perform the checks (for all controls on the dialog) and transfer the data to the member variables. Or you can put some error-displaying controls (usually in red color), activated when an error is found, like in .net or the web.