MFC OnEnChange handler function - infinite loop

Question

(I'm using VS++2005)

I put edit box control (with ID - ID_edit_box) on my dialog, and associate (with handler wizard) two varibles for it: control (c_editbox) and value (v_editbox) variable. Also I associate handler function OnEnChangeedit_box with that edit box control. Suppose that we may enter just one digit in edit box, and that digit can be 0 or 1. If we enter some other value - what I want is that content of that edit box is automaticaly cleared, so user can't see that he type anything (in other words user can not enter anything except 0/1 in edit box). I do that check in onEnChangeedit_box function. Here is the code:

void CSDRDlg::OnEnChangeedit_box()
{
   CWnd* pWnd;
   CString edit_box_temp;

   pWnd = GetDlgItem(ID_edit_box);
   pWnd->GetWindowText(edit_box_temp);

   if ((edit_box_temp == "0" || edit_box_temp == "1")
   {...do something - i.e. setfocus on some other edit box }
   else
   {
       pWnd->SetWindowText(""); // clear the content of edit box
       //... any other statement below will not be executed because the 
       //above line cause again call of this function
   }
}

I debug and discover that line: pWnd->SetWindowText(""); cause an infinite loop because we change control content in this function which triggers again her call.

But I change above code like this:

void CSDRDlg::OnEnChangeedit_box()
{
   UpdateData(TRUE);
   if ((v_editbox == "0" || v_editbox== "1")
   {...do something - i.e. setfocus on some other edit box }
   else
   { 
      v_editbox = "";
      UpdateData(FALSE);
   }
}

and that works what I want but can someone explain to me why when we call

  v_editbox = "";
  UpdateData(FALSE);

that doesn't cause an infinite loop.

score 1 · Answer 1 · edited Jan 30 '13 at 15:32

1

Why don't you Set Min/Max value to 0/1 or Set Value Type as bool when you Add Variable for your EditBox

edited Jan 30 '13 at 15:32

MrsTang

3,119
1
19
24

answered Jan 30 '13 at 15:13

rheoJacob

11
1

score 0 · Answer 2 · answered Aug 06 '09 at 21:43

You should probably do this by subclassing CEdit and filter out invalid characters. eg:

class CSDREdit public CEdit
{
    afx_msg void OnChar(UINT nChar, UINT nRepCnt, UINT nFlags);
    DECLARE_MESSAGE_MAP()
};

BEGIN_MESSAGE_MAP(CSDREdit, CEdit)
    ON_WM_CHAR()
END_MESSAGE_MAP()

void CSDREdit::OnChar(UINT nChar, UINT nRepCnt, UINT nFlags)
{
    if (nChar != _T('0') && nChar != _T('1'))
        return;
    CEdit::OnChar(nChar, nRepCnt, nFlags);
}

MFC OnEnChange handler function - infinite loop

2 Answers2