Re: CWindow::Create Failure

From:
"Ben Voigt" <rbv@nospam.nospam>
Newsgroups:
microsoft.public.vc.language
Date:
Wed, 18 Oct 2006 17:02:25 -0500
Message-ID:
<uKidZEw8GHA.3736@TK2MSFTNGP02.phx.gbl>
"NickP" <a@a.com> wrote in message
news:%23urEpEh8GHA.2092@TK2MSFTNGP03.phx.gbl...

Hi there,

   I have a class derived from CWindowImpl and I am handling the WM_CREATE
message via a message handler and map.

   -----------

   BEGIN_MSG_MAP(CMyWindow)
       MESSAGE_HANDLER(WM_CREATE, OnCreate)
   END_MSG_MAP()

   LRESULT OnCreate(UINT /*uMsg*/, WPARAM /*wParam*/, LPARAM /*lParam*/,
BOOL& /*bHandled*/);

   LRESULT CFlashView::OnCreate(UINT /*uMsg*/, WPARAM /*wParam*/, LPARAM
lParam, BOOL& /*bHandled*/)
   {
       #if FLASH
           cWndChildWindow = CWindow::Create(WC_MYWINDOWCLASS, m_hWnd,
NULL, NULL, WS_CHILD);
           cWndChildWindow.ShowWindow(SW_SHOW);
       #endif
       return(0);
   }

   -----------

   In the OnCreate method I would like to create an instance of a child
window that needs to be displayed in this window. But for some reason I
am greeted with an Assertion Failure with the expression

   m_hWnd == 0
   ...
   ATLASSUME(m_hWnd == NULL)

   Now is this telling me that m_hWnd needs to be 0? or can't be 0?

   m_hWnd is the handle to CMyWindow and at this point it should have been
created right? This is really confusing me, if I pass 0 to the method it


Although I see you solved your problem, it might help to clarify this as
well.
When WM_CREATE is sent (it is sent, not posted), the window exists, but
CreateWindow has not yet returned. So if you had code looking like:
static HWND hMainWnd;
hMainWnd = ::CreateWindow(...);
Then hMainWnd would not be assigned yet during WM_CREATE. Instead, the HWND
is passed as the first parameter to WndProc. Since ATL doesn't share that
first parameter with you, I expect it has already used it to set m_hWnd and
initialize whatever lookup tables / hash dictionary it uses to map between
C++ objects and HWNDs.

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