HOWTO: Handle OCM_CTLCOLORxxx Reflected Messages

• The Microsoft Foundation Classes (MFC) included with: Microsoft Visual C++, 32-bit Edition, version 4.0, 4.1, 4.2, 5.0

SUMMARY

This article shows you how to change the background color of an OLE control that subclasses a Windows Control, with sample code for an Edit control.

This article should apply to Button, Static, ListBox, and ComboBox controls as well.

MORE INFORMATION

Please refer to the following article in the Microsoft Knowledge Base:

   ARTICLE_ID : Q130952
   TITLE      : WM_CTLCOLORxxx Message Changes for Windows 95

To change the background color of an OLE Control that subclasses an Edit Control, you must handle the OCM_CTLCOLOREDIT(32-bit) messages. These messages are intercepted by the "reflector window" (created for an OLE control that subclasses a Windows control) that reflects them back to the OLE control itself. In response to these reflected messages, you must set the background color (and optionally the foreground color) and return a handle to a brush initialized with the background color.

Step-by-Step Example

The sample code in this example illustrates how to handle OCM_CTLCOLOREDIT in order to change the background color of an OLE control that subclasses an Edit control

1. Generate an MFC ActiveX Control Wizard Application, and select the option that allows you to subclass an Edit control.

2. To handle an OCM_CTLCOLOREDIT reflected window message, declare the following handler function in the .h file of your control's class:

         LRESULT OnOcmCtlColor(WPARAM wParam, LPARAM lParam);
   

3. In the .cpp file of your control's class, add an ON_MESSAGE entry to the message map:

         ON_MESSAGE(OCM_CTLCOLOREDIT, OnOcmCtlColor)
   

4. Also in the .cpp file, implement the OnOcmCtlColor member function to process the reflected message:

         // Assuming CEdtclrCtrl is the class for this control
         LRESULT CEdtclrCtrl::OnOcmCtlColor(WPARAM wParam, LPARAM lParam)
         {
           //Declare CBrush* m_pBackBrush in your control's .h file
           if (m_pBackBrush == NULL)
              m_pBackBrush = new CBrush(RGB(0,0,0));
           CDC* pdc = CDC::FromHandle((HDC)wParam);
           pdc->SetBkMode(TRANSPARENT);
           pdc->SetBkColor(RGB(0,0,0));
           pdc->SetTextColor(RGB(0,255,0));
           HBRUSH far* hbr = (HBRUSH far*)m_pBackBrush->GetSafeHandle();
           return ((DWORD)hbr);
         }
   
   

1. Build and register your control.

2. Insert this control into the ActiveX Control Test Container. Notice that the background color of your OLE control is changed.

REFERENCES