CreateWindowEx返回NULL [英] CreateWindowEx returns NULL

问题描述

以下是我的代码的一部分.每次我运行该程序时，SPanel的CreateWindowEx返回NULL，从而触发错误.谁能看到这段代码有什么问题吗?

The following is a portion of my code. Every time I run the program, CreateWindowEx of the SPanel returns NULL, triggering an error. Can anyone see what is wrong with this piece of code?

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

SPanelProc and MainWndProc are declared already, and is of the prototype LRESULT CALLBACK SPanelProc (HWND hWnd, UINT msg, WPARAM wParam, LPARAM lParam);.

我正在编程的环境是Visual C ++ 2010.

The environment I'm programming in is 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);
}

推荐答案

每个窗口过程都必须在每条消息上返回DefWindowProc(hwnd,msg,wparam,lparam)，当您使用自定义绘制过程时，WM_ERASEBKGND和WM_PAINT之类的消息除外(您必须返回0，这样操作系统才不会使用默认过程重新绘制窗口)

Every window procedure MUST return DefWindowProc(hwnd,msg,wparam,lparam) on every message, with exceptions on messages like WM_ERASEBKGND and WM_PAINT when you are using your custom painting procedure (you must return 0 so the OS doesn't the repaint the window with it's default procedure)

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