MFC CToolBar update mechanism bug?

Question

In Visual Studio, MFC CToolBar buttons are updated by ON_UPDATE_COMMAND_UI which is sent during idle state. I suppose this mechanism is buggy if I change enable/disable state of the button in ON_UPDATE_COMMAND_UI handler.

Specifically:

Suppose the button is now in enabled state. At a certain time, the code 'wants' the button to be disabled (and of-course should not be clicked by user), but the button will be really disabled at next idle period, as in following figure:

In red area in the figure, the code state, in my opinion, is unstable and the developer must handle this unstable state by checking the button state manually. I have no idea if I have missed something or have some misunderstanding of this mechanism?

PS: The procedure for Menu is OK. It always calls ON_UPDATE_COMMAND_UI handler and check the button state before ON_COMMAND handler.

My question is how to make the ON_UPDATE_COMMAND_UI handler be called before ON_COMMAND handler just like Menus do?

Answer 1

After debugging and tracing, I finally found a possible solution. Key codes are listed here to help others with the same problem. Override OnCommand as follows:

BOOL CMainDlg::OnCommand(WPARAM wParam, LPARAM lParam)
{
    // Disable WM_COMMAND reflection for ToolBar control
    // makes the ON_UPDATE_COMMAND_UI handler be called 
    // right before ON_COMMAND handler.

    if ((HWND)lParam == m_wndToolBar.GetSafeHwnd())
        lParam = NULL;

    return CDialog::OnCommand(wParam, lParam);
}

The side effect is WM_COMMAND reflection is disabled for ToolBar, but it would be OK in most cases.

Answer 2

As I just ran into this so I thought I'd add my solution. I have a button to paste records into a database and so it is clear for the client, I only wanted the button enabled if there is valid data on the clip board. Here is what it looks like:

My App in the back and notepad++ in front with records selected. When I 'ctrl C' the text in notepad++ the 'I' on my tool bar becomes active even though my app is idle. My app is part of the clipboard chain and gets notified. This is the WM_DRAWCLIPBOARD handler.

LRESULT CMainFrame::OnDrawClipboard(  WPARAM wparam, LPARAM lparam  )
{
    if( hWndClipboardChain )
        ::SendMessage( hWndClipboardChain, WM_DRAWCLIPBOARD, wparam, lparam );

    if( wparam )
        PostMessage( ID_CLIPBOARD_HASCHANGED, 0, 0 );

    return TRUE;
}

From there I post to my app not getting in the way of the WM_DRAWCLIPBOARD message, and there:

LRESULT CMainFrame::OnCheckClipboard(  WPARAM wparam, LPARAM lparam  )
{
    std::string data( GetClipboardStr( ) );
    std::string::size_type end_cnt= data.find( "\r\n" );
    if( end_cnt == std::string::npos )
        bClipboardHasValidRecords= false;
    else
    {
        auto header_end= data.begin( ) + end_cnt;
        csv_vect_t header;
        split( header, str_it_range_t( data.begin( ), header_end ), boost::is_any_of("\t") );

        bClipboardHasValidRecords= header.size( ) == RARECORD_SIZE;
    }
    return TRUE;
}

The main thread of my app is waken up by the messages and the 'I' will turn on and off without making the app an active window. And it just happens without any extra code.