win32开发（消息机制）

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    win32真正的本质其实就是消息机制。大家如果调试win32程序，就会发现win32的应用其实是一个单线程代码，这至少说明windows提供的demo code是单线程应用。既然是单线程应用，那么基本上说明这个应用是一个dead loop代码。作为循环代码来说，它不可能一直在运行，那么势必会阻塞在某一个地方，或者在某一个函数里面，否则cpu占有率会一直保持在100%了。

    想到这，大家或许就清楚了，win32其实就是一个消息处理的应用。所有的处理都是通过消息回调的形式进行的。换句话说就是，你只要处理好系统发给你的消息就可以了，剩下的就是你把对应的回调函数准备好就ok了，大体就是这个意思。

// tt.cpp : Defines the entry point for the application.//#include "stdafx.h"#include "resource.h"#define MAX_LOADSTRING 100// Global Variables:HINSTANCE hInst;// current instanceTCHAR szTitle[MAX_LOADSTRING];// The title bar textTCHAR szWindowClass[MAX_LOADSTRING];// The title bar text// Foward declarations of functions included in this code module:ATOMMyRegisterClass(HINSTANCE hInstance);BOOLInitInstance(HINSTANCE, int);LRESULT CALLBACKWndProc(HWND, UINT, WPARAM, LPARAM);LRESULT CALLBACKAbout(HWND, UINT, WPARAM, LPARAM);int APIENTRY WinMain(HINSTANCE hInstance,                     HINSTANCE hPrevInstance,                     LPSTR     lpCmdLine,                     int       nCmdShow){ // TODO: Place code here.MSG msg;HACCEL hAccelTable;// Initialize global stringsLoadString(hInstance, IDS_APP_TITLE, szTitle, MAX_LOADSTRING);LoadString(hInstance, IDC_TT, szWindowClass, MAX_LOADSTRING);MyRegisterClass(hInstance);// Perform application initialization:if (!InitInstance (hInstance, nCmdShow)) {return FALSE;}hAccelTable = LoadAccelerators(hInstance, (LPCTSTR)IDC_TT);// Main message loop:while (GetMessage(&msg, NULL, 0, 0)) {if (!TranslateAccelerator(msg.hwnd, hAccelTable, &msg)) {TranslateMessage(&msg);DispatchMessage(&msg);}}return msg.wParam;}////  FUNCTION: MyRegisterClass()////  PURPOSE: Registers the window class.////  COMMENTS:////    This function and its usage is only necessary if you want this code//    to be compatible with Win32 systems prior to the 'RegisterClassEx'//    function that was added to Windows 95. It is important to call this function//    so that the application will get 'well formed' small icons associated//    with it.//ATOM MyRegisterClass(HINSTANCE hInstance){WNDCLASSEX wcex;wcex.cbSize = sizeof(WNDCLASSEX); wcex.style= CS_HREDRAW | CS_VREDRAW;wcex.lpfnWndProc= (WNDPROC)WndProc;wcex.cbClsExtra= 0;wcex.cbWndExtra= 0;wcex.hInstance= hInstance;wcex.hIcon= LoadIcon(hInstance, (LPCTSTR)IDI_TT);wcex.hCursor= LoadCursor(NULL, IDC_ARROW);wcex.hbrBackground= (HBRUSH)(COLOR_WINDOW+1);wcex.lpszMenuName= (LPCSTR)IDC_TT;wcex.lpszClassName= szWindowClass;wcex.hIconSm= LoadIcon(wcex.hInstance, (LPCTSTR)IDI_SMALL);return RegisterClassEx(&wcex);}////   FUNCTION: InitInstance(HANDLE, int)////   PURPOSE: Saves instance handle and creates main window////   COMMENTS:////        In this function, we save the instance handle in a global variable and//        create and display the main program window.//BOOL InitInstance(HINSTANCE hInstance, int nCmdShow){   HWND hWnd;   hInst = hInstance; // Store instance handle in our global variable   hWnd = CreateWindow(szWindowClass, szTitle, WS_OVERLAPPEDWINDOW,      CW_USEDEFAULT, 0, CW_USEDEFAULT, 0, NULL, NULL, hInstance, NULL);   if (!hWnd)   {      return FALSE;   }   ShowWindow(hWnd, nCmdShow);   UpdateWindow(hWnd);   return TRUE;}////  FUNCTION: WndProc(HWND, unsigned, WORD, LONG)////  PURPOSE:  Processes messages for the main window.////  WM_COMMAND- process the application menu//  WM_PAINT- Paint the main window//  WM_DESTROY- post a quit message and return////LRESULT CALLBACK WndProc(HWND hWnd, UINT message, WPARAM wParam, LPARAM lParam){int wmId, wmEvent;PAINTSTRUCT ps;HDC hdc;TCHAR szHello[MAX_LOADSTRING];LoadString(hInst, IDS_HELLO, szHello, MAX_LOADSTRING);switch (message) {case WM_COMMAND:wmId    = LOWORD(wParam); wmEvent = HIWORD(wParam); // Parse the menu selections:switch (wmId){case IDM_ABOUT:   DialogBox(hInst, (LPCTSTR)IDD_ABOUTBOX, hWnd, (DLGPROC)About);   break;case IDM_EXIT:   DestroyWindow(hWnd);   break;default:   return DefWindowProc(hWnd, message, wParam, lParam);}break;case WM_PAINT:hdc = BeginPaint(hWnd, &ps);// TODO: Add any drawing code here...RECT rt;GetClientRect(hWnd, &rt);DrawText(hdc, szHello, strlen(szHello), &rt, DT_CENTER);EndPaint(hWnd, &ps);break;case WM_DESTROY:PostQuitMessage(0);break;default:return DefWindowProc(hWnd, message, wParam, lParam);   }   return 0;}// Mesage handler for about box.LRESULT CALLBACK About(HWND hDlg, UINT message, WPARAM wParam, LPARAM lParam){switch (message){case WM_INITDIALOG:return TRUE;case WM_COMMAND:if (LOWORD(wParam) == IDOK || LOWORD(wParam) == IDCANCEL) {EndDialog(hDlg, LOWORD(wParam));return TRUE;}break;}    return FALSE;}

    这个代码大体出现过很多次。其实最重要的地方就三个，一个是MyRegisterClass函数，它最重要的意义就是定义了WndProc这个回调入口，它告诉os所有的消息响应，你直接call这个函数就可以了。当然，如果是mdi程序，还是要定义多个WNDCLASSEX的。第二个函数就是InitInstance，它的意义就是创建了一个句柄为hWnd的窗口，一个app可以创建很多个窗口，但是所有的窗口消息入口都是WndProc。这里的多窗口指的是多窗口控件。注意这里szWindowClass参数的意义。第三个函数毫无疑问，就是WndProc。它是真正处理消息的地方，这些消息有些只会出现一次，比如WM_DESTROY。有些会不停出现，比如WM_PAINT、WM_SIZE这些。至于About函数，其实它就是DialogBox的回调入口，本质上和WndProc是一样的。如果大家有兴趣，会发现About函数处理的时候，回溯堆栈里面就有WndProc，这说明他们其实都是在处理消息而已。

    至于消息是什么时候获取的，大家看这个循环就可以了，

// Main message loop:while (GetMessage(&msg, NULL, 0, 0)) {if (!TranslateAccelerator(msg.hwnd, hAccelTable, &msg)) {TranslateMessage(&msg);DispatchMessage(&msg);}}

    有消息的时候就处理消息，如果系统没有给app发送消息，那么GetMessage会被block住。如果换成另外一个函数PeekMessage，那基本上就是deadloop了，所以两个函数其实是不一样的。windows的消息大体分成三种，一种是WM_COMMAND，这种处理菜单、工具栏等消息。一种是WM_NOTIFY，它处理组件送过来的信息，比如list控件、tree控件等等。第三种就是系统消息，这包括WM_PAINT，WM_CREATE，WM_SIZE，WM_DESTROY等等。学到什么消息，就用什么消息就可以了。