一个简单的SDK程序， CreateWindow了一个Button子窗口，接着用SetWindowLong函数来指定该Button的回调函数为ButtonProc。程序的目标效果为点击窗口中的按钮后，会在窗口中输出一段文字。
问题在于用SetWindowLong函数为Button指定的回调函数未起作用，所以也就无法得到目标效果了。
下面是完整的程序代码，不知问题出在哪儿了

C/C++ code

#include <windows.h>

#define IDC_BUTTON 101

BOOL InitApplication(HINSTANCE);
BOOL InitInstance(HINSTANCE, int);
LRESULT CALLBACK WndProc(HWND hwnd, UINT uMsg, WPARAM wParam, LPARAM lParam);
LRESULT CALLBACK ButtonProc(HWND hwnd, UINT uMsg, WPARAM wParam, LPARAM lParam);
//int WINAPI WinMain(HINSTANCE, HINSTANCE, LPSTR, int);

static TCHAR szAppName[] = TEXT("MainWClass");
WNDPROC BTNProc;
HWND hwndButton;

int WINAPI WinMain(HINSTANCE hInstance,
                                   HINSTANCE hPrevInstance,
                                   LPSTR lpCmdLine,
                                   int nCmdShow)
{
        MSG msg;

        if (!InitApplication(hInstance))
        {
                return (FALSE);
        }

        if (!InitInstance(hInstance, nCmdShow))
        {
                return (FALSE);
        }

        while(GetMessage(&msg, NULL, 0, 0))
        {
                TranslateMessage(&msg);
                DispatchMessage(&msg);
        }

        return (msg.wParam);

}

BOOL InitApplication(HINSTANCE hinstance)
{

        WNDCLASS wcx;
        //wcx.cbSize = sizeof(wcx);
        wcx.style = CS_HREDRAW | CS_VREDRAW;
        wcx.lpfnWndProc = (WNDPROC)WndProc;
        wcx.cbClsExtra = 0;
        wcx.cbWndExtra = 0;
        wcx.hInstance = hinstance;
        wcx.hIcon = LoadIcon(NULL, IDI_APPLICATION);
        wcx.hCursor = LoadCursor(NULL, IDC_ARROW);
        wcx.hbrBackground = GetStockObject(WHITE_BRUSH);
        wcx.lpszMenuName = NULL;
        wcx.lpszClassName = szAppName;

        return (RegisterClass(&wcx));
}

BOOL InitInstance(HINSTANCE hinstance, int nCmdShow)
{
        HWND hwnd;
        HINSTANCE hinst = hinstance;

        hwnd = CreateWindow(szAppName,
                                TEXT("SDK"),
                                                WS_OVERLAPPEDWINDOW,
                                                CW_USEDEFAULT,
                                                CW_USEDEFAULT,
                                                CW_USEDEFAULT,
                                                CW_USEDEFAULT,
                                                NULL,
                                                NULL,
                                                hinstance,
                                                NULL);
        if (!hwnd)
        {
                return (FALSE);
        }

        ShowWindow(hwnd, nCmdShow);
        UpdateWindow(hwnd);
        return (TRUE);
}

LRESULT CALLBACK WndProc(HWND hwnd, UINT uMsg, WPARAM wParam, LPARAM lParam)
{
        HDC hdc;

        RECT rect;
        PAINTSTRUCT ps;
        //RECT rect;

        switch(uMsg)
        {
        case WM_CREATE:
                hwndButton = CreateWindow(TEXT("BUTTON"),
                                              TEXT("OK"),
                                                                  WS_VISIBLE | WS_CHILD | BS_DEFPUSHBUTTON,
                                                                  10,
                                                                  10,
                                                                  100,
                                                                  27,
                                                                  hwnd,
                                                                  (HMENU) IDC_BUTTON,
                                                                  (HINSTANCE) GetWindowLong(hwnd, GWL_HINSTANCE),
                                                                  NULL);

                BTNProc = (WNDPROC) SetWindowLong(hwndButton,
                                                      GWL_WNDPROC,
                                                                                   (LPARAM)(WNDPROC)ButtonProc);
                return 0;
        case WM_PAINT:
                hdc = BeginPaint(hwnd, &ps);
                EndPaint(hwnd, &ps);
                break;
        case WM_DESTROY:
                PostQuitMessage(0);
        }

        return DefWindowProc(hwnd, uMsg, wParam, lParam);
}
LRESULT CALLBACK ButtonProc(HWND hwnd, UINT uMsg, WPARAM wParam, LPARAM lParam)
{
        HDC hdc;
        RECT rect;
        switch(uMsg)
        {
        case WM_PAINT:
                break;
        case WM_COMMAND:
                switch(LOWORD(wParam))
                {
                case IDC_BUTTON:
                        hdc = GetDC(hwnd);
                        TextOut(hdc, 100, 100, TEXT("Mouse Left Button Click!"), strlen("Mouse Left Button Click!"));
                        ReleaseDC(hwnd, hdc);

                        ValidateRect(hwnd, &rect);
                        break;
                }
                break;
        }
        return CallWindowProc(BTNProc, hwnd, uMsg, wParam, lParam);
}

关注

你的回调函数已经起作用了，问题是Button本身是接收不到WM_COMMAND消息的，这个消息是用来通知父窗体的，只要把WM_COMMAND放到WndProc里就能收到。

楼上正解.当Button被点击,会发送BN_CLICKED给你窗口,所以WM_COMMAND只能写在父窗口中