> I have an app which creates a window and C# and needs to pass the
> window handle (HWND) and App Instance (HINSTANCE) to a C++ dll
> whicj will do some direct show stuff. I have created the C++ MFC app and
> pass the
> window.Handle (System.IntPtr)
>
> There is a wrapper which looks like:
> [ DllImport("vpCSILib.dll")]
> public static extern void setWnd(System.IntPtr wnd);
>
> the c++ prototype is:
> __declspec(dllexport) void CvpCSILibApp::setWnd(HWND win);
>
> the method does
> HWND m_hwndHandle=win;
>
> sometimes it works. most time not, get a System.NullRefernceException in the
> c++ dll though the pointer has a value going in. For giggles, I set managed
> extentions on to debug from the c# and the win value is unused.

"Robert Jordan" wrote:

> Hi,
>
> > I have an app which creates a window and C# and needs to pass the
> > window handle (HWND) and App Instance (HINSTANCE) to a C++ dll
> > whicj will do some direct show stuff. I have created the C++ MFC app and
> > pass the
> > window.Handle (System.IntPtr)
> >
> > There is a wrapper which looks like:
> > [ DllImport("vpCSILib.dll")]
> > public static extern void setWnd(System.IntPtr wnd);
> >
> > the c++ prototype is:
> > __declspec(dllexport) void CvpCSILibApp::setWnd(HWND win);
> >
> > the method does
> > HWND m_hwndHandle=win;
> >
> > sometimes it works. most time not, get a System.NullRefernceException in the
> > c++ dll though the pointer has a value going in. For giggles, I set managed
> > extentions on to debug from the c# and the win value is unused.
>
> This is probably not an interop issue. Window handles get
> sometimes recreated by WinForms. Is the window already visible
> when you pass its handle to the C++ DLL?
>
> Rob