How do I get notification from a `CEdit` box?

Question

I have a CEdit box where a user can enter relevant information. As soon as he\she starts writing in the box, I need a notification so that I can call doSomething() to perform some other task. Does Windows provide a callback, and if so, how do I use it?

Answer 1

With MFC there's no callback as such, rather you do this by implementing a handler for the appropriate event. You need to handle one of two events: WM_CHAR or EN_CHANGE

Handle the dialog's EN_CHANGE for example duplicating in realtime the entered text elsewhere on the dialog. You need to firstly add an entry in the dialog's message map, and secondly override the appropriate handler:

BEGIN_MESSAGE_MAP(CstackmfcDlg, CDialog)
    ON_EN_CHANGE(IDC_EDIT1, &CstackmfcDlg::OnEnChangeEdit1)
END_MESSAGE_MAP()

void CstackmfcDlg::OnEnChangeEdit1()
    {
    CString text;
    m_edit.GetWindowText(text);
    m_label.SetWindowText(text); // update a label control to match typed text
    }

Or, handle the editbox class's WM_CHAR for example preventing input of certain characters, e.g. ignore anything other than a digit for numerical entry. Derive a class from CEdit, handle the WM_CHAR event of that class (not the dialog) and make your edit control an instance of that class.

BEGIN_MESSAGE_MAP(CCtrlEdit, CEdit)
    ON_WM_CHAR()
END_MESSAGE_MAP()

void CCtrlEdit::OnChar(UINT nChar, UINT nRepCnt, UINT nFlags)
    {
    // Do nothing if not numeric chars entered, otherwise pass to base CEdit class
    if ((nChar >= '0' && nChar <= '9') || VK_BACK == nChar)
        CEdit::OnChar(nChar, nRepCnt, nFlags);
    }

Note that you can use the VS IDE to put in stubs for the handler overrides by using the Properties bar with the mouse selection in the message map block.

EDIT: Added example code, and corrected explanation of WM_CHAR which I had wrong.