PeekMessage与GetMessage区别

原文地址：http://www.cnblogs.com/faceang/archive/2010/05/25/1743757.html

 

PeekMessage与GetMessage的对比
相同点：
           PeekMessage函数与GetMessage函数都用于查看应用程序消息队列，有消息时将队列中 的消息派发出去。

不同点：
          无论应用程序消息队列是否有消息，PeekMessage函数都立即返回，程序得以继续执行后面的语句（无消息则执行其它指令，有消息时一般要将消息派发出去，再执行其它指令）。GetMessage函数只有在消息对立中有消息时返回，队列中无消息就会一直等，直至下一个消息出现时才返回。在等的这段时间，应用程序不能执行任何指令。

（从他们的不同点上来看，PeekMessage函数有点像“乞丐行乞”，有你就施舍点，没有也不强。GetMessage函数有点像“强盗打劫”，有你得给，没有我就等你什么时候有了再给，这段时间我什么都不干，我就等你。）

下面的程序用来在窗体内画随机生成的矩形，分别使用PeekMessage函数和GetMessage函数实现，读者可以种实际效果看出他们两者的区别。

<span style="font-size:18px;">#include <windows.h>
#include <stdlib.h>           // for the rand function

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

int cxClient, cyClient ;

int WINAPI WinMain (HINSTANCE hInstance,HINSTANCE hPrevInstance,
                    PSTR szCmdLine,int iCmdShow)
{
     static TCHAR szAppName[] = TEXT ("RandRect") ;
     HWND         hwnd ;
     MSG          msg ;
     WNDCLASS     wndclass ;

     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 ;
     }

     hwnd = CreateWindow (szAppName, TEXT ("Random Rectangles"),
                          WS_OVERLAPPEDWINDOW,
                          CW_USEDEFAULT, CW_USEDEFAULT,
                          CW_USEDEFAULT, CW_USEDEFAULT,
                          NULL, NULL, hInstance, NULL) ;

     ShowWindow (hwnd, iCmdShow) ;
     UpdateWindow (hwnd) ;

     //用于替换的部分
    while (TRUE)
     {
          if (PeekMessage (&msg, NULL, 0, 0, PM_REMOVE))
          {
               if (msg.message == WM_QUIT)
                    break ;
               TranslateMessage (&msg) ;
               DispatchMessage (&msg) ;
          }
          else
               DrawRectangle (hwnd) ;
     }
    //用于替换的部分
     return msg.wParam ;
}

LRESULT CALLBACK WndProc (HWND hwnd,UINT iMsg, WPARAM wParam,LPARAM

lParam)
{
     switch (iMsg)
     {
     case WM_SIZE:
          cxClient = LOWORD (lParam) ;
          cyClient = HIWORD (lParam) ;
          return 0 ;

     case WM_DESTROY:
          PostQuitMessage (0) ;
          return 0 ;
     }
     return DefWindowProc (hwnd, iMsg, wParam, lParam) ;
}

void DrawRectangle (HWND hwnd)
{
     HBRUSH hBrush ;
     HDC    hdc ;
     RECT   rect ;

     if (cxClient == 0 || cyClient == 0)
          return ;

     SetRect (&rect, rand () % cxClient, rand () % cyClient,
                     rand () % cxClient, rand () % cyClient) ;

     hBrush = CreateSolidBrush (
                    RGB (rand () % 256, rand () % 256, rand () % 256)) ;
     hdc = GetDC (hwnd) ;

     FillRect (hdc, &rect, hBrush) ;
     ReleaseDC (hwnd, hdc) ;
     DeleteObject (hBrush) ;
}</span>

<span style="font-size:18px;">#include <windows.h>
#include <stdlib.h>           // for the rand function

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

int cxClient, cyClient ;

int WINAPI WinMain (HINSTANCE hInstance, HINSTANCE hPrevInstance,
                    PSTR szCmdLine, int iCmdShow)
{
     static TCHAR szAppName[] = TEXT ("RandRect") ;
     HWND         hwnd ;
     MSG          msg ;
     WNDCLASS     wndclass ;

     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 ;
     }

     hwnd = CreateWindow (szAppName, TEXT ("Random Rectangles"),
                          WS_OVERLAPPEDWINDOW,
                          CW_USEDEFAULT, CW_USEDEFAULT,
                          CW_USEDEFAULT, CW_USEDEFAULT,
                          NULL, NULL, hInstance, NULL) ;

     ShowWindow (hwnd, iCmdShow) ;
     UpdateWindow (hwnd) ;

     //用于替换的部分
    while (TRUE)
     {
          if (PeekMessage (&msg, NULL, 0, 0, PM_REMOVE))
          {
               if (msg.message == WM_QUIT)
                    break ;
               TranslateMessage (&msg) ;
               DispatchMessage (&msg) ;
          }
          else
               DrawRectangle (hwnd) ;
     }
    //用于替换的部分
     return msg.wParam ;
}

LRESULT CALLBACK WndProc (HWND hwnd, UINT iMsg, WPARAM wParam, LPARAM

lParam)
{
     switch (iMsg)
     {
     case WM_SIZE:
          cxClient = LOWORD (lParam) ;
          cyClient = HIWORD (lParam) ;
          return 0 ;

     case WM_DESTROY:
          PostQuitMessage (0) ;
          return 0 ;
     }
     return DefWindowProc (hwnd, iMsg, wParam, lParam) ;
}

void DrawRectangle (HWND hwnd)
{
     HBRUSH hBrush ;
     HDC    hdc ;
     RECT   rect ;

     if (cxClient == 0 || cyClient == 0)
          return ;

     SetRect (&rect, rand () % cxClient, rand () % cyClient,
                     rand () % cxClient, rand () % cyClient) ;

     hBrush = CreateSolidBrush (
                    RGB (rand () % 256, rand () % 256, rand () % 256)) ;
     hdc = GetDC (hwnd) ;

     FillRect (hdc, &rect, hBrush) ;
     ReleaseDC (hwnd, hdc) ;
     DeleteObject (hBrush) ;
}</span>

以上程序用PeekMessage函数实现，在应用程序消息队列没有消息时，随机生成的矩形将坚持不懈地画下去。当有消息产生时，PeekMessage函数获取并派发消息出去，然后继续画随机生成的矩形。

下面部分代码用于替换WinMain函数中“用于替换的部分”的代码。

<span style="font-size:18px;">while (TRUE)
     {
          if (GetMessage (&msg, NULL, 0, 0))
          {
               if (msg.message == WM_QUIT)
                    break ;
               TranslateMessage (&msg) ;
               DispatchMessage (&msg) ;
           DrawRectangle (hwnd) ;
          }
          else
                break;
     }</span>

<span style="font-size:18px;">while (TRUE)
     {
          if (GetMessage (&msg, NULL, 0, 0))
          {
               if (msg.message == WM_QUIT)
                    break ;
               TranslateMessage (&msg) ;
               DispatchMessage (&msg) ;
           DrawRectangle (hwnd) ;
          }
          else
                break;
     }</span>

替换后，应用程序产生一个消息（鼠标移动、改变窗体大小等），在窗体内画一个随机生成的矩形，无消息产生时，窗体无变化。