Customized Check Boxes

Environment: VC6 SP4, Win 2000 SP2

Owner-Drawn push buttons have been well covered until now, but what about check boxes?

At first I was surprised that, although being one of the basic controls under Windows, I couldn’t find anything useful about customized check boxes. I soon realised why: Windows doesn’t support Owner-Drawn check boxes. You can assign the BS_OWNERDRAW style to them, but this won’t be any help. Then you would receive WM_DRAWITEM messages for the default, pushed, and disabled states, just like for an ordinary Owner-Drawn push button.

A check box, however, has more states; first, it can be checked or unchecked; then, the left mouse button or space bar can be pressed in any of the basic states; and, it can also be disabled in any of them. That’s six different states. So, is it impossible to make customized check boxes? No, the fact that we can’t rely on WM_DRAWITEM only means that there will be more work for you. You have to determine yourself when to redraw the check box and in which state to do it. But that is where CCheckBox comes in: It does all this for you internally. You only have to provide a bitmap with all six possible check mark states to it.

About CCheckBox

CCheckBox is a class derived from the MFC CButton class. Besides CTor and Dtor, it only has one public member:

static bool drawFocus;  // true  => draw focus rectangle (default)
                        // false => don’t draw focus rectangle

How to Integrate CCheckBox into Your Application

1. Prepare a bitmap with all six possible check mark states. RGB(255,0,255) is the transparency color.
2. Declare a CCheckBox member variable in your CDialog derive class:

   CCheckBox   m_cb_1;

3. Call the CCheckBox’s constructor from the constructor of your dialog:

   CYourDialog::CYourDialog () :
       m_cb_1 (IDB_STATES, 13)
   { }      // IDB_STATES: ID of bitmap resource,
            // prepared in step 1
            // 13: dimension (width=height) of check mark
   

4. Now, attach the check box to CCheckBox, either in OnInitDialog:

   // Subclass IDC_CBOX (= ID of check box)
   m_cb_1.SubclassDlgItem(ID_CBOX, this);
   

   or in DoDataExchange:

   // Subclass IDC_CBOX
   DDX_Control(pDX, IDC_CBOX, m_cb_1);