CreateWindowEx returns NULL

Question

以下是我代码的一部分。每次我运行该程序时，CreateWindowEx SPanel 都会返回 NULL ，触发错误。任何人都可以看到这段代码有什么问题吗？

SPanelProc和MainWndProc已经声明，并且是原型LRESULT CALLBACK SPanelProc (HWND hWnd, UINT msg, WPARAM wParam, LPARAM lParam);。

我正在编程的环境是Visual C++ 2010。

为什么CreateWindowEx总是返回NULL？

#include <Windows.h>
#include <WindowsX.h>
LRESULT CALLBACK SPanelProc (HWND hWnd, UINT msg, WPARAM wParam, LPARAM lParam)
{
    switch (msg)
    {
        case WM_MOUSEMOVE:
        break;
    }
    return 0;
}
void Init ()
{
    HWND child;
    HINSTANCE hInstance = (HINSTANCE)(GetWindowLongPtr (parent, GWLP_HINSTANCE));
    WNDCLASSEX wc;
    const char PanelClassName[] = "SPanel"; //ClassName of the panel. Do not reuse on another window
    //Create the window, initialize GWLP_USERDATA, check for errors, register the window class, and hide the window

    //Create the windowclass for the button
    wc.cbSize        = sizeof (WNDCLASSEX);
    wc.style         = 0;
    wc.lpfnWndProc   = SPanelProc;
    wc.cbClsExtra    = 0;
    wc.cbWndExtra    = 0;
    wc.hInstance     = hInstance;
    wc.hIcon         = LoadIcon (hInstance, IDI_APPLICATION);
    wc.hCursor       = LoadCursor (hInstance, IDC_ARROW);
    wc.hbrBackground = (HBRUSH)(COLOR_WINDOW + 1);
    wc.lpszMenuName  = NULL;
    wc.lpszClassName = PanelClassName;
    wc.hIconSm       = LoadIcon (hInstance, IDI_APPLICATION);
    //If could not register window class
    if(!RegisterClassEx (&wc))
    {
        MessageBox (NULL, "Panel registration failed!", "Error!", MB_OK);
        PostQuitMessage (0);
        return;
    }
    //Create window
    child = CreateWindowEx (WS_EX_NOPARENTNOTIFY, PanelClassName, "TITLE_TEXT", WS_CHILD, 0, 0, 400, 200, parent, NULL, hInstance, NULL);
    //Check for error in window creation
    if (child == NULL)
    {
        MessageBox (NULL, "Panel creation failed!", "Error!", MB_OK);
        PostQuitMessage (0);
        return;
    }
    return;
}

int WINAPI WinMain (HINSTANCE hInstance, HINSTANCE hPrevInstance, LPSTR lpCmdLine, int nCmdShow)
{
    WNDCLASSEX wc;
    HWND hWnd;
    MSG Msg;
    int length, width;
    //Register the window, create the window, and check for errors
    {
        //Window class
        wc.cbSize        = sizeof (WNDCLASSEX);
        wc.style         = 0;
        wc.lpfnWndProc   = MainWndProc;
        wc.cbClsExtra    = 0;
        wc.cbWndExtra    = 0;
        wc.hInstance     = hInstance; //Instance used to create the window
        wc.hIcon         = LoadIcon (hInstance, MAKEINTRESOURCE (IDI_CODERICON)); //Change here to change large application icon
        wc.hCursor       = LoadCursor (hInstance, IDC_ARROW); //Change here to change application cursor
        wc.hbrBackground = (HBRUSH)(COLOR_WINDOW + 1); //Change here to change starting background color (white)
        wc.lpszMenuName  = NULL;
        wc.lpszClassName = Coder::Constants::MAINWNDCLASSNAME;
        wc.hIconSm       = (HICON)LoadImage (hInstance, MAKEINTRESOURCE (IDI_CODERICON), IMAGE_ICON, GetSystemMetrcs (SM_CXSMICON), GetSystemMetrics (SM_CYSMICON), 0); //Change here to change application icon (small, as in taskbar)
        //Register the window class so that the ClassName can be used to create the window and then check for error
        if (!RegisterClassEx (&wc))
        {
            MessageBox (NULL, "Main window registration failed!", "Error!", MB_OK);
            return 0;
        }
        //Get screen dimensions
        length = GetSystemMetrics (SM_CXSCREEN);
        width = GetSystemMetrics (SM_CYSCREEN);
        //Create window
        hWnd = CreateWindowEx (WS_EX_CLIENTEDGE, /*Border*/
            Coder::Constants::MAINWNDCLASSNAME,
            Coder::Constants::MAINWNDTITLETEXT, /*Title of window*/
            WS_OVERLAPPED | WS_SYSMENU | WS_MINIMIZEBOX | WS_THICKFRAME | WS_CLIPCHILDREN, /*Window style*/
            (length - Coder::Constants::XDEFAULT - Coder::Constants::XSHIFT) / 2, (width - Coder::Constants::YDEFAULT - Coder::Constants::YSHIFT) / 2, /*Top-left x and y coordinates*/
            Coder::Constants::XDEFAULT + Coder::Constants::XSHIFT, Coder::Constants::YDEFAULT + Coder::Constants::YSHIFT, /*Lengths and widths of window*/
            NULL, NULL, 
            hInstance, NULL);
        //Check for error in window creation
        if (hWnd == NULL)
        {
            MessageBox (NULL, "Main window creation failed!", "Error!", MB_OK);
            return 0;
        }
    }
    //Call function
            Init (hWnd);
    //Show and redraw the window
    ShowWindow (hWnd, nCmdShow);
    UpdateWindow (hWnd);
    //Put window in message loop
    while (GetMessage (&Msg, NULL, 0, 0) > 0) //While not terminated
    {
        TranslateMessage (&Msg);
        DispatchMessage (&Msg);
    }
    //Return
    return static_cast<int>(Msg.wParam);
}

Answer 1

每个窗口过程都必须在每条消息上返回DefWindowProc(hwnd,msg,wparam,lparam)，但使用自定义绘制过程时WM_ERASEBKGND和WM_PAINT等消息除外（您必须返回 0，以便操作系统不会使用其默认过程重新绘制窗口）