《编程思想之消息机制》一文中我们讲了消息的相关概念和消息机制的模拟，本文将进一步聊聊C++中的消息机制。

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从简单例子探析核心原理

在讲之前，我们先看一个简单例子：创建一个窗口和两个按钮，用来控制窗口的背景颜色。其效果如下：

图 2 ：效果图

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Win32Test.h

#pragma once

#include 
   
     #include 
    
      #include 
     
       //资源ID #define ID_BUTTON_DRAW 1000 #define ID_BUTTON_SWEEP 1001 // 注册窗口类 ATOM AppRegisterClass(HINSTANCE hInstance); // 初始化窗口 BOOL InitInstance(HINSTANCE, int); // 消息处理函数(又叫窗口过程) LRESULT CALLBACK WndProc(HWND, UINT, WPARAM, LPARAM); // (白色背景)按钮事件 void OnButtonWhite(); // (灰色背景)按钮事件 void OnButtonGray(); // 绘制事件 void OnDraw(HDC hdc);
     
    
   

Win32Test.cpp

#include stdafx.h
#include Win32Test.h


//字符数组长度
#define MAX_LOADSTRING 100

//全局变量
HINSTANCE hInst;                                            // 当前实例
TCHAR g_szTitle[MAX_LOADSTRING] = TEXT(Message process);  // 窗口标题
TCHAR g_szWindowClass[MAX_LOADSTRING] = TEXT(AppTest);    // 窗口类的名称
HWND g_hWnd;                                                // 窗口句柄
bool g_bWhite = false;                                      // 是否为白色背景

//WinMain入口函数
int APIENTRY _tWinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance, LPTSTR lpCmdLine, int nCmdShow)
{
    UNREFERENCED_PARAMETER(hPrevInstance);
    UNREFERENCED_PARAMETER(lpCmdLine);
    // 注册窗口类
    if(!AppRegisterClass(hInstance))
    {
         return (FALSE);
    }
    // 初始化应用程序窗口
    if (!InitInstance (hInstance, nCmdShow))
    {
        return FALSE;
    }

    // 消息循环
    MSG msg;
    while (GetMessage(&msg, NULL, 0, 0))
    {
        TranslateMessage(&msg);
        DispatchMessage(&msg);
    }
    return (int) msg.wParam;
}



// 注册窗口类
ATOM AppRegisterClass(HINSTANCE hInstance)
{
    WNDCLASSEX wcex;
    wcex.cbSize = sizeof(WNDCLASSEX);
    wcex.style          = CS_HREDRAW | CS_VREDRAW;
    wcex.lpfnWndProc    = WndProc;
    wcex.cbClsExtra     = 0;
    wcex.cbWndExtra     = 0;
    wcex.hInstance      = hInstance;
    wcex.hIcon          = LoadIcon(NULL, IDI_APPLICATION);
    wcex.hCursor        = LoadCursor(NULL, IDC_ARROW);
    wcex.hbrBackground  = (HBRUSH)(COLOR_WINDOW+1);
    wcex.lpszMenuName   = NULL;
    wcex.lpszClassName  = g_szWindowClass;
    wcex.hIconSm        = NULL;

    return RegisterClassEx(&wcex);
}



// 保存实例化句柄并创建主窗口
BOOL InitInstance(HINSTANCE hInstance, int nCmdShow)
{  
   hInst = hInstance; // 保存handle到全局变量
   g_hWnd = CreateWindow(g_szWindowClass, g_szTitle, WS_OVERLAPPEDWINDOW, 0, 0, 400, 300, NULL, NULL, hInstance, NULL);
   // 创建按钮
   HWND hBtWhite = CreateWindowEx(0, LButton, L白色, WS_CHILD | WS_VISIBLE | BS_TEXT, 100, 100, 50, 20, g_hWnd, (HMENU)ID_BUTTON_DRAW, hInst, NULL);
   HWND hBtGray = CreateWindowEx(0, LButton, L灰色, WS_CHILD | WS_VISIBLE | BS_CENTER, 250, 100, 50, 20, g_hWnd, (HMENU)ID_BUTTON_SWEEP, hInst, NULL);

   if (!g_hWnd)
   {
      return FALSE;
   }
   ShowWindow(g_hWnd, nCmdShow);
   UpdateWindow(g_hWnd);

   return TRUE;
}



// (窗口)消息处理
LRESULT CALLBACK WndProc(HWND hWnd, UINT message, WPARAM wParam, LPARAM lParam)
{
    int wmId, wmEvent;
    PAINTSTRUCT ps;
    HDC hdc;

    switch (message)
    {
    case WM_COMMAND:
        wmId    = LOWORD(wParam);
        //wmEvent = HIWORD(wParam);

        switch (wmId)
        {
        case ID_BUTTON_DRAW:
            OnButtonWhite();
            break;
        case ID_BUTTON_SWEEP:
            OnButtonGray();
            break;
        default:
            return DefWindowProc(hWnd, message, wParam, lParam);
        }
        break;
    case WM_PAINT:
        hdc = BeginPaint(hWnd, &ps);
        OnDraw(hdc);
        EndPaint(hWnd, &ps);
        break;
    case WM_DESTROY:
        PostQuitMessage(0);
        break;
    default:
        return DefWindowProc(hWnd, message, wParam, lParam);
    }
    return 0;
}



//事件处理

//按下hBtWhite时的事件
void OnButtonWhite()
{
    g_bWhi