in MFC when CEdit control reached the maximum characters, backspace doesn't work

Question

in my dialog, there is a CEdit box, which set maximum character number. below in DoDataExchange function:

void CDlgSurvey::DoDataExchange(CDataExchange* pDX)
{
    DDX_Control(pDX, IDC_EDIT_SURVEY_ID, m_SurveyIDEdit);//ACUTALLY THE ISSUE IS HERE,SO LATER WE MODIFIED THE CLASS FUNCTION Onchar in m_SurveyIDEdit RELATED
    DDX_Text(pDX, IDC_EDIT_SURVEY_ID, m_SurveyID);
    DDV_MaxChars(pDX, m_SurveyID, SURVEY_ID_FIELD_LENGTH);
}

I found it works. it means I cannot key in characters more than SURVEY_ID_FIELD_LENGTH. But the problem is when I already key in the SURVEY_ID_FIELD_LENGTH length of characters, and I tried to delete some character by using backspace at the end of text. it doesn't work. Did somebody met such problem? and I also try to using another way to set max text in OnInitDialog,

BOOL CDlgSurvey::OnInitDialog()
{
    //set Max Text in Edit Box
    CEdit* pEditControl = (CEdit*)GetDlgItem(IDC_EDIT_SURVEY_ID);
    if (pEditControl)
    {
        pEditControl->SetLimitText(SURVEY_ID_FIELD_LENGTH);
    }

    return TRUE;  // return TRUE unless you set the focus to a control
                  // EXCEPTION: OCX Property Pages should return FALSE
}

the problem is the same, again, I cannot use backspace after it reached the maximum character. Does someone have any idea on how to fix it? thanks,

Answer 1

After checking the code, it is not related to SetLimitText or DDV_MaxChars . The actual issue relates to DDX_Control .

With variable m_SurveyIDEdit we check the character restriction. Once we find the text length has already been reached ( MaxLength ), it just simply returns. That's the problem.

So we have modified the code. We still handle the CEdit::OnChar method. So the key point to handle the issue is: Every time you should examine all unrelated code and see what happens.

My edit control was actually derived from CRestrictedEdit . My solution was to adjust the OnChar handler.

void CRestrictedEdit::OnChar(UINT nChar, UINT nRepCnt, UINT nFlags)
{
    // Get the text of the edit control
    CString sText;
    GetWindowText(sText);

    // if the control limit is already reached, no need to validate the character.
    if ((static_cast<UINT>(sText.GetLength())) == this->GetLimitText())
    {
        CEdit::OnChar(nChar, nRepCnt, nFlags); //THIS IS NEW LINE ADDED
        return;
    }
}