How to change the back color of an edit box when it gets the focus

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Introduction

This article shows how to change the back color of an edit box when it gets the focus.

1. Derive a class from the standard edit control class, CEdit.
2. Add 3 private variables:
   • A COLORREF to store the current back color
   • A CBrush to store the brush used to paint the back color of the edit control
   • A CString to store the current contents of the edit box
3. Override the virtual OnChildNotify function.

   BOOL CMyEdit::OnChildNotify(UINT message, 
       WPARAM wParam, LPARAM lParam, LRESULT* pLResult)
   {
       // We only want to handle WM_CTLCOLOREDIT messages - 32 bit only
       if (message != WM_CTLCOLOREDIT) 
       {
           return CEdit::OnChildNotify(message, wParam, lParam, pLResult);
       }
       HDC hdcChild = (HDC)wParam;
       // Text is black – you can modify this by adding
       // another variable for text color
       SetTextColor(hdcChild, RGB(0,0,0));
       SetBkColor(hdcChild, m_BackColor);
       return TRUE;
   }

4. Add message handlers to handle the following Windows messages:
   • ON_WM_SETFOCUS
   • ON_WM_KILLFOCUS
   • ON_WM_PAINT

   void CMyEdit::OnSetFocus(CWnd* pOldWnd)
   {
       CEdit::OnSetFocus(pOldWnd);
   
       m_BackColor = RGB(255,255,0);
       Invalidate(FALSE);
   }
   
   void CMyEdit::OnKillFocus(CWnd* pNewWnd)
   {
       CEdit::OnKillFocus(pNewWnd);
       // I am setting normal back color to white
       // – you can modify this as you see fit
       m_BackColor = RGB(255,255,255);
       // Force a repaint
       Invalidate(FALSE);
   }

   void CMyEdit::OnPaint()
   {
       CPaintDC dc(this); // device context for painting
   
       // TODO: Add your message handler code here
       GetWindowText(m_Text);
       SetBkGrndColor();
   
       // Do not call CEdit::OnPaint() for painting messages
   }
   

5. Add a private member function SetBkGrndColor()

   void CMyEdit::SetBkGrndColor()
   {
       // Delete the old brush
       m_Brush.DeleteObject();
       // Create a new brush in the specified color
       m_Brush.CreateSolidBrush(m_BackColor);
       CDC* pDC = GetDC();
       pDC->SetBkMode(OPAQUE);
       pDC->SetBkColor(m_BackColor);
       // Select the brush into this window’s device context
       pDC->SelectObject(&m_Brush);
       CRect rc;
       // Get the client area of the edit control
       GetClientRect(&rc);
       ScreenToClient(&rc);
       // Apply the device context to the client area of the edit control
       pDC->Rectangle(0, 0, rc.Width(), rc.Height());
       // Rewrite the text since the backcolor paint
       // overwrote the existing text
       pDC->SetTextColor(RGB(0, 0, 0,));
       pDC->TextOut(2, 2, m_Text.GetBuffer(m_Text.GetLength()));
   }

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