API消息機制中的WM_COMMAND

在WM_COMMAND消息中 , lParam參數沒有高地位的值之分 . 如果這個消息是由一個窗口發送的 , 那麼這個參數lParam就表示這個窗口的窗口句柄HWND，這個主要是爲了區分消息是從哪個按鈕(或其它窗口控件)發送來的。

//button.c

#include<windows.h>

 

//按鈕個數

#define NUM        2

 

//按鈕的文本

TCHAR*  btnName[NUM]={TEXT("按鈕1"), TEXT("按鈕2")};

 

LRESULT CALLBACK WndProc(HWND, UINT, WPARAM, LPARAM);

 

int WINAPI WinMain(HINSTANCE hInstance,

                   HINSTANCE hPrevInstance,

                   PSTR szCmdLine,

                   int iCmdShow)

{

    static  TCHAR   szAppName[] = TEXT("Btn");

    HWND            hwnd;

    MSG             msg;

    WNDCLASS        wndclass;

    int             cxScreen, cyScreen;

     

    wndclass.style          = CS_HREDRAW | CS_VREDRAW;

    wndclass.lpfnWndProc    = WndProc;

    wndclass.cbClsExtra     = 0;

    wndclass.cbWndExtra     = 0;

    wndclass.hInstance      = hInstance;

    wndclass.hIcon          = LoadIcon(NULL, IDI_APPLICATION);

    wndclass.hCursor        = LoadCursor(NULL, IDC_ARROW);

    wndclass.hbrBackground  = (HBRUSH)GetStockObject(WHITE_BRUSH);

    wndclass.lpszMenuName   = NULL;

    wndclass.lpszClassName  = szAppName;

     

    if(!RegisterClass(&wndclass))

    {

        MessageBox(NULL, TEXT("This program requires Windows NT!"),

            szAppName, MB_ICONERROR);

        return 0;

    }

     

    cxScreen = GetSystemMetrics(SM_CXSCREEN);

    cyScreen = GetSystemMetrics(SM_CYSCREEN);

    hwnd = CreateWindow(szAppName,

                        TEXT("Btn Demo"),

                        WS_OVERLAPPEDWINDOW,

                        cxScreen * 3 / 10,

                        cyScreen / 5,

                        cxScreen * 2 / 5,

                        cyScreen * 3 / 5,

                        NULL,

                        NULL,

                        hInstance,

                        NULL);

 

    ShowWindow(hwnd, iCmdShow);

    UpdateWindow(hwnd);

 

    while(GetMessage(&msg, NULL, 0, 0))

    {

        TranslateMessage(&msg);

        DispatchMessage(&msg);

    }

     

    return msg.wParam;

}

 

LRESULT CALLBACK WndProc(HWND hwnd, UINT message, WPARAM wParam, LPARAM lParam)

{

    static HWND        hwndBtn[NUM];//按鈕句柄

    HINSTANCE       hInstance;  //窗口實例

    int             cxChar, cyChar, i;//默認字體的寬度和高度 循環變量

     

    switch(message)

    {

    case WM_CREATE:

        cxChar = LOWORD(GetDialogBaseUnits());

        cyChar = HIWORD(GetDialogBaseUnits());

        hInstance = ((LPCREATESTRUCT)lParam)->hInstance;

         

        //創建兩個按鈕

        for(i=0; i<NUM; i++)

            hwndBtn[i] = CreateWindow(TEXT("button"), btnName[i],

                                    WS_CHILD | WS_VISIBLE | BS_DEFPUSHBUTTON,

                                    10, i * 100 + 10, 20 * cxChar, 7 * cyChar / 4,

                                    hwnd, (HMENU)9, hInstance, NULL);

          return 0;

 

    case WM_COMMAND:

        //響應兩個按鈕的按下消息

        for(i=0; i<NUM; i++)

            //如果按鈕句柄匹配  就顯示相應信息

            if((HWND)lParam == hwndBtn[i])

            {

                MessageBox(NULL, btnName[i], TEXT("提示"), MB_OK);

                break;

            }

        return 0;

 

    case WM_DESTROY:

        PostQuitMessage(0);

        return 0;

    }

 

    return DefWindowProc(hwnd, message, wParam, lParam);

}