MFC: Changing the colour of CEdit

Question

Guys, can someone give me a brief run through of how to change the background colour of a CEdit control at runtime? I want to be able to change the background to red if the field is zero length and the normal white otherwise.

Answer 1

You cannot do it with a plain CEdit, you need to override a few bits.

Implement your own ON_WM_CTLCOLOR_REFLECT handler, then return your coloured CBrush in the handler:

(roughly, you'll need to put the usual resource management in there, rememebr to delete your brush in the destructor)

class CColorEdit : public CEdit
{
  ....
  CBrush   m_brBkgnd;
  afx_msg HBRUSH CtlColor(CDC* pDC, UINT nCtlColor)
  {
    m_brBkgnd.DeleteObject();
    m_brBkgnd.CreateSolidBrush(nCtlColor);
  }
}

Answer 2

This can also be done without deriving from CEdit:

1. Add ON_WM_CTLCOLOR() to your dialog's BEGIN_MESSAGE_MAP() code block.

2. Add OnCltColor() to your dialog class:

   afx_msg HBRUSH OnCtlColor(CDC* pDC, CWnd* pWnd, UINT nCtlColor);
   

3. Implement OnCtlColor() like so:

   HBRUSH CMyDialog::OnCtlColor(CDC* pDC, CWnd* pWnd, UINT nCtlColor)
   {
       if ((CTLCOLOR_EDIT == nCtlColor) &&
           (IDC_MY_EDIT == pWnd->GetDlgCtrlID()))
       {
           return m_brMyEditBk; //Create this brush in OnInitDialog() and destroy in destructor
       }
       return CDialog::OnCtlColor(pDC, pWnd, nCtlColor);
   }