WTL - Button Menu

• Download demo project - 16 Kb
• Download source files - 3 Kb

DevStudio's Tools|Customize menu displays a dialog box that contains a button control with an arrow on it. When pressed, the button will display a drop-down menu. I needed this feature in my ATL applications, but didn't want the overhead of MFC or the headache of Win32. So I borrowed from Norm Almond's excellent example of Cool Push Menu Button and ported it to WTL, simplifying it's functionality along the way. I'm not implying anything was wrong with what Norm developed...the control just did more than I needed it to. I will eventually port his entire control to WTL, when time allows.

Caveats

CButtonMenu is derived from CButtonMenuImpl. To draw the arrow on the button, CButtonMenuImpl needs to have the BS_OWNERDRAW style set. However, this will send the WM_DRAWITEM msg to the parent of the CButtonMenuImpl, and not the CButtonMenuImpl itself. By subclassing the parent HWND, the CButtonMenuImpl can hijack the msg and handle it alone. To do this, the CButtonMenuImpl has a private member CContainedWindow variable that subclasses the parent. Then, using the ALT_MSG_MAP() macro, we can catch the msg:

class CButtonMenuImpl : ...
{
CContainedWindow m_Parent;
public:
    CButtonMenuImpl():
      m_Parent(this,1){}

    {other code}
protected:
    typedef CWindowImpl<T, TBase, TWinTraits> baseClass;
    BEGIN_MSG_MAP(CButtonMenuImpl)
        other msgs
    ALT_MSG_MAP(1)
        MESSAGE_HANDLER(WM_DRAWITEM, OnDrawItem)
    END_MSG_MAP()
        {other code}

};

Finally, to make simple use of this control, CButtonMenu provides an operator overload:

class CButtonMenu : public CButtonMenuImpl<CButtonMenu>
{
public:
    DECLARE_WND_SUPERCLASS(_T("WTL_CButtonMenu"), GetWndClassName())
//ZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZ
    CButtonMenu& operator=(HWND hWnd)
    {
        if ( m_hWnd )
            DestroyWindow();
        if ( ::IsWindow(hWnd) )
            SubclassWindow(hWnd);
        return *this;
    }
};

Here's an example of how to initialize a CButtonMenu with a button already on a dialog:

    // Member variable of dialog
    CButtonMenu btnMenu;        

    // Somewhere in WM_INITDIALOG handler
    btnMenu = GetDlgItem(IDC_BTN_ABOUT);
    btnMenu.AddMenuItem(IDC_MNU_ONE,"Windows");
    btnMenu.AddMenuItem(IDC_MNU_TWO,"Template");
    btnMenu.AddMenuItem(IDC_MNU_THREE,"",MF_SEPARATOR);
    btnMenu.AddMenuItem(IDC_MNU_FOUR,"Library");

When the user selects a menu item, a msg will be sent to the dialog.

Deficiencies

Doesn't provide a Create method that will initialize the control properly (yet)

Doesn't respond to the BS_DEFPUSHBUTTON flag

History

August 14, 2000 - Fixed the OnDraw method to use the DRAWITEMSTRUCT's HWND instead of the Button's HWND when calling GetWindowText(). This fixed a bug that resulted in two different CButtonMenu's on the same dialog always painting the same caption.