RegisterClassEx fails with error 87

[rpetz]

I'm trying to create a window using this library but I am running into a roadblock while registering the window class struct - it just returns with error code 87 - The parameter is incorrect.

Running this code nearly identically in C++ creates a window without issue, and I have tried so many different configurations of the WNDCLASSEXW struct but nothing seems to make the issue disappear.

(Obviously this code doesn't call CreateWindowEx yet as I omitted that here since I cannot get past this error)

fixed (char* dll = "user32.dll")
fixed (char* lpClassName = "myWindowClass")
fixed (char* lpWindowName = "My Window")
{
    var hInstance = PInvoke.GetModuleHandle(dll);
    var wc = new WNDCLASSEXW
    {
        style = WNDCLASS_STYLES.CS_HREDRAW | WNDCLASS_STYLES.CS_VREDRAW,
        lpfnWndProc = Wndproc,
        cbClsExtra = 0,
        cbWndExtra = 0,
        hInstance = hInstance,
        hIcon = PInvoke.LoadIcon(HINSTANCE.Null, PInvoke.IDI_APPLICATION),
        hCursor = PInvoke.LoadCursor(HINSTANCE.Null, PInvoke.IDC_ARROW),
        hbrBackground = new HBRUSH(new IntPtr(0x6)), // 0x6 is what a C++ compiler generates, I'd love to know how to get the COLOR_WINDOW brush through CsWin32
        lpszMenuName = null,
        lpszClassName = lpClassName,
        hIconSm = PInvoke.LoadIcon(HINSTANCE.Null, PInvoke.IDI_APPLICATION)
    };
    wc.cbSize = (uint)Marshal.SizeOf(wc); // I also have tried Marshal.SizeOf<WNDCLASSEXW>() with no luck    

    var regResult = PInvoke.RegisterClassEx(in wc);

    var errorCode = Marshal.GetLastWin32Error();
    var errorMessage = new Win32Exception(errorCode).Message;
}

My WndProc func resides in the same class and is as follows:

private LRESULT Wndproc(HWND hwnd, uint msg, WPARAM wParam, LPARAM lParam)
{
    switch (msg)
    {
        case PInvoke.WM_CLOSE:
        {
            Debug.WriteLine("Closing Window");
            PInvoke.DestroyWindow(hwnd);
            break;
        }
        case PInvoke.WM_DESTROY:
        {
            Debug.WriteLine("Destroying Window");
            PInvoke.PostQuitMessage(0);
            break;
        }
        case PInvoke.WM_KEYUP:
        {
            Debug.WriteLine("Key Up Event");
            break;
        }
        default:
        {
            PInvoke.DefWindowProc(hwnd, msg, wParam, lParam);
            break;
        }
    }

    return new LRESULT(0);
}

What am I missing? At this point I feel like Mr Magoo just poking around until I finally get something right on this haha

[rpetz]

Well it would appear I was not very knowledgeable on what module HINSTANCE should be referencing - using the Marshal class I was able to have it grab the correct instance

var hInstance = new HINSTANCE(Marshal.GetHINSTANCE(typeof([insert your type here]).Module));