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;
}

Answer 2

I m not a hundred percent sure, but it seems like the some_control_ CEdit control is not registered with the parent window. I think you will need to call some_control_.Create(...) with the parent handle as a parameter.

see msdn article for a documentation of CEdit::Create().

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