Question

I have a WTL 8.0 SDI application for Windows Mobile 5. In this contrived example below, I create a view, destroy it, then re-create it. But, when it’s re-created assertions in the WM_INITDIALOG handler fail because the control’s HWND isn’t valid.

I note that I can fix this by handling WM_DESTROY in CMyView and manually destroying every child control. But, I didn’t think I should have to. MSDN even says:

This message is sent first to the
window being destroyed and then to the
child windows (if any) as they are
destroyed.

Anybody have an idea as to what’s going on?

Edit: If I handle WM_NCDESTROY in CMyView, all of the the child control handles are still valid! (some_control_.IsWindow()==TRUE) That’s not how it’s supposed to be…

Thanks,
PaulH

class CMyView : public CDialogImpl< CMyView >,
                public CWinDataExchange< CMyView >
{
    // <snip> Message Map and other standard WTL macros </snip>

    LRESULT OnInitDialog( UINT /*uMsg*/, WPARAM /*wParam*/, LPARAM /*lParam*/, BOOL& /*bHandled*/ )
    {
        DoDataExchange( FALSE );
        // assertion fails within the SetWindowText() call
        // atlwin.h line 876
        // ATLASSERT(::IsWindow(m_hWnd));
        some_control_.SetWindowText( _T( "Foo" ) );
        return 0;
    };

private:
    CEdit some_control_;
}; // class CMyView

class CMainFrame : public CFrameWindowImpl< CMainFrame >, 
                   public CUpdateUI< CMainFrame >,
                   public CMessageFilter, 
                   public CIdleHandler
{
public:
    // <snip> Message Map and other standard WTL macros </snip>

    BOOL CMainFrame::PreTranslateMessage( MSG* pMsg )
    {
        if( CFrameWindowImpl< CMainFrame >::PreTranslateMessage( pMsg ) )
            return TRUE;

        return my_view_.PreTranslateMessage( pMsg );
    };

    LRESULT OnCreate( UINT /*uMsg*/, WPARAM /*wParam*/, LPARAM /*lParam*/, BOOL& /*bHandled*/ )
    {
        CMessageLoop* pLoop = _Module.GetMessageLoop();
        ATLASSERT( pLoop != NULL );
        pLoop->AddMessageFilter( this );
        pLoop->AddIdleHandler( this );

        m_hWndClient = my_view_.Create( m_hWnd );
        my_view_.DestroyWindow();
        m_hWndClient = my_view_.Create( m_hWnd );
    };

private:
    CMyView my_view_;
}; // class CMainFrame

Answer 1

It is not good practice to Create, Destroy and re-Create the same window, you should consider hiding it and reinitializing your contents when showing it again.

Anyhow your code will not ASSERT at re-creation with:

virtual void CMyView::OnFinalMessage(HWND)
{
    some_control_.m_hWnd = 0;
}