windows是如何擦除背景的？？？？？？？

Question

LRESULT CALLBACK WndProc(HWND hWnd, UINT message, WPARAM wParam, LPARAM lParam
)
{
    int wmId, wmEvent;
    PAINTSTRUCT ps;
    HDC hdc;
    RECT wndREC;    switch (message) 
    {
    case WM_COMMAND:
        wmId    = LOWORD(wParam); 
        wmEvent = HIWORD(wParam); 
        // 分析菜单选择:
        switch (wmId)
        {
        case IDM_ABOUT:
            //::SendMessage(hWnd,9999,0,0);
            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);
//        EndPaint(hWnd, &ps);
        //break;
    case WM_DESTROY:
        PostQuitMessage(0);
        break;
    case WM_CHAR:
        ::CreateWindow("myWnd","aa",WS_CHILD|WS_VISIBLE|WS_CAPTION|WS_THICKFRA
ME,100,100,300,300,hWnd,NULL,hInst,NULL);
        break;
    case 9999:
        hdc = GetDC(hWnd);
        TextOut(hdc,100,100,"helllow",7);
        DeleteDC(hdc);
        break;
    default:
        return DefWindowProc(hWnd, message, wParam, lParam);
    }
    return 0;
}假如我产生两个子窗口在主窗口下，然后两个字窗口重叠，再把下面的子窗口移出来，就
会发现该窗口背景没有擦除，似乎上面还有一个窗口似的，
假如发送WM_ERASEBACKGROUND消息，又只有客户区擦除，其余地方还是那样。

Answer 1

// 32.cpp : 定义应用程序的入口点。
//#include "stdafx.h"
#include "32.h"
#define MAX_LOADSTRING 100// 全局变量:
HINSTANCE hInst; // 当前实例
TCHAR szTitle[MAX_LOADSTRING]; // 标题栏文本
TCHAR szWindowClass[MAX_LOADSTRING]; // 主窗口类名// 此代码模块中包含的函数的前向声明:
ATOM MyRegisterClass(HINSTANCE hInstance);
BOOL InitInstance(HINSTANCE, int);
LRESULT CALLBACK WndProc(HWND, UINT, WPARAM, LPARAM);
LRESULT CALLBACK WndProc2(HWND, UINT, WPARAM, LPARAM);
LRESULT CALLBACK About(HWND, UINT, WPARAM, LPARAM);int APIENTRY _tWinMain(HINSTANCE hInstance,
                     HINSTANCE hPrevInstance,
                     LPTSTR    lpCmdLine,
                     int       nCmdShow)
{
  // TODO: 在此放置代码。
MSG msg;
HACCEL hAccelTable; // 初始化全局字符串
LoadString(hInstance, IDS_APP_TITLE, szTitle, MAX_LOADSTRING);
LoadString(hInstance, IDC_MY, szWindowClass, MAX_LOADSTRING);
MyRegisterClass(hInstance); // 执行应用程序初始化:
if (!InitInstance (hInstance, nCmdShow)) 
{
return FALSE;
} hAccelTable = LoadAccelerators(hInstance, (LPCTSTR)IDC_MY); // 主消息循环:
while (GetMessage(&msg, NULL, 0, 0)) 
{
if (!TranslateAccelerator(msg.hwnd, hAccelTable, &msg)) 
{
TranslateMessage(&msg);
DispatchMessage(&msg);
}
} return (int) msg.wParam;
}//
//  函数: MyRegisterClass()
//
//  目的: 注册窗口类。
//
//  注释: 
//
//    仅当希望在已添加到 Windows 95 的
//    “RegisterClassEx”函数之前此代码与 Win32 系统兼容时，
//    才需要此函数及其用法。调用此函数
//    十分重要，这样应用程序就可以获得关联的
//   “格式正确的”小图标。
//
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_MY);
wcex.hCursor = LoadCursor(NULL, IDC_ARROW);
wcex.hbrBackground = (HBRUSH)::GetStockObject(WHITE_BRUSH);
wcex.lpszMenuName = (LPCTSTR)IDC_MY;
wcex.lpszClassName = szWindowClass;
wcex.hIconSm = LoadIcon(wcex.hInstance, (LPCTSTR)IDI_SMALL); RegisterClassEx(&wcex);
wcex.hbrBackground = (HBRUSH)::GetStockObject(GRAY_BRUSH);
wcex.lpszClassName = "myWnd";
wcex.lpfnWndProc = (WNDPROC)WndProc2;
return RegisterClassEx(&wcex);
}//
//   函数: InitInstance(HANDLE, int)
//
//   目的: 保存实例句柄并创建主窗口
//
//   注释: 
//
//        在此函数中，我们在全局变量中保存实例句柄并
//        创建和显示主程序窗口。
//
BOOL InitInstance(HINSTANCE hInstance, int nCmdShow)
{
   HWND hWnd;   hInst = hInstance; // 将实例句柄存储在全局变量中   hWnd = CreateWindowEx(WS_EX_CLIENTEDGE,szWindowClass, szTitle, WS_OVERLAPPEDWINDOW|WS_VSCROLL|WS_HSCROLL,
      CW_USEDEFAULT, 0, CW_USEDEFAULT, 0, NULL, NULL, hInstance, NULL);   if (!hWnd)
   {
      return FALSE;
   }   ShowWindow(hWnd, nCmdShow);
   UpdateWindow(hWnd);   return TRUE;
}//
//  函数: WndProc(HWND, unsigned, WORD, LONG)
//
//  目的: 处理主窗口的消息。
//
//  WM_COMMAND - 处理应用程序菜单
//  WM_PAINT - 绘制主窗口
//  WM_DESTROY - 发送退出消息并返回
//
//
LRESULT CALLBACK WndProc(HWND hWnd, UINT message, WPARAM wParam, LPARAM lParam)
{
int wmId, wmEvent;
PAINTSTRUCT ps;
HDC hdc;
RECT wndREC; switch (message) 
{
case WM_COMMAND:
wmId    = LOWORD(wParam); 
wmEvent = HIWORD(wParam); 
// 分析菜单选择:
switch (wmId)
{
case IDM_ABOUT:
//::SendMessage(hWnd,9999,0,0);
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);
// EndPaint(hWnd, &ps);
//break;
case WM_DESTROY:
PostQuitMessage(0);
break;
case WM_CHAR:
::CreateWindow("myWnd","aa",WS_CHILD|WS_VISIBLE|WS_CAPTION|WS_THICKFRAME,100,100,300,300,hWnd,NULL,hInst,NULL);
break;
case 9999:
hdc = GetDC(hWnd);
TextOut(hdc,100,100,"helllow",7);
DeleteDC(hdc);
break;
default:
return DefWindowProc(hWnd, message, wParam, lParam);
}
return 0;
}
LRESULT CALLBACK WndProc2(HWND hWnd, UINT message, WPARAM wParam, LPARAM lParam)
{
static int i;
int wmId, wmEvent;
PAINTSTRUCT ps;
HDC hdc;
RECT wndREC;
char szStr[16]; switch (message) 
{
case WM_COMMAND:
wmId    = LOWORD(wParam); 
wmEvent = HIWORD(wParam); 
// 分析菜单选择:
switch (wmId)
{
case IDM_ABOUT:
//::SendMessage(hWnd,9999,0,0);
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:
// GetWindowRect(hWnd,&wndREC);
// InvalidateRect(hWnd,&wndREC,TRUE);
i++;
memset(szStr,0,16);
itoa(i,szStr,10);
::SetWindowText(hWnd,szStr);
hdc = BeginPaint(hWnd, &ps);
// TextOut(hdc,100,100,"helllow",7);

EndPaint(hWnd, &ps);
// UpdateWindow(hWnd);
break;
case WM_MOVE:
// MessageBox(hWnd,"ss","ss",MB_OK);
hdc = GetDC(hWnd);
SendMessage(hWnd,WM_ERASEBKGND,(DWORD)hdc,0);
ReleaseDC(hWnd,hdc);
break;
case WM_DESTROY:
PostQuitMessage(0);
break;
case 9999:
hdc = GetDC(hWnd);
TextOut(hdc,100,100,"helllow",7);
DeleteDC(hdc);
break;
default:
return DefWindowProc(hWnd, message, wParam, lParam);
}
return 0;
}// “关于”框的消息处理程序。
LRESULT CALLBACK About(HWND hDlg, UINT message, WPARAM wParam, LPARAM lParam)
{
HWND hWnd;
HDC hdc;
switch (message)
{
case WM_INITDIALOG:
return TRUE; case WM_COMMAND:
if (LOWORD(wParam) == IDCANCEL) 
{
EndDialog(hDlg, LOWORD(wParam));
return TRUE;
}
if(LOWORD(wParam) == IDOK  )
{
hWnd = GetParent(hDlg);
hdc = GetDC(hWnd);
TextOut(hdc,0,0,"ggggggg",7);
ReleaseDC(hWnd,hdc);
::SendMessage(hWnd,9999,0,0);
return TRUE;
}
break;
}
return FALSE;
}

Answer 2

只有客户区被擦除？你再试试WM_NCPAINT。

Answer 3

你应该重新注册一个子窗口类
ATOM MyRegisterClass(HINSTANCE hInstance);
ATOM MyRegisterClass1(HINSTANCE hInstance);int APIENTRY _tWinMain(HINSTANCE hInstance,
                     HINSTANCE hPrevInstance,
                     LPTSTR    lpCmdLine,
                     int       nCmdShow)
{
  MSG msg;
HACCEL hAccelTable; MyRegisterClass(hInstance);
MyRegisterClass1(hInstance);         ... return (int) msg.wParam;
}ATOM MyRegisterClass1(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 = 0;
wcex.hCursor = 0;
wcex.hbrBackground = (HBRUSH)::GetStockObject(WHITE_BRUSH);
wcex.lpszMenuName = 0;
wcex.lpszClassName = "MY_CHILD";
wcex.hIconSm = 0; RegisterClassEx(&wcex);
wcex.hbrBackground = (HBRUSH)::GetStockObject(GRAY_BRUSH);
wcex.lpszClassName = "myChild";
wcex.lpfnWndProc = (WNDPROC)WndProc2;
return RegisterClassEx(&wcex);
}

Answer 4

case WM_CHAR:
::CreateWindow("myChild","aa",WS_POPUP|WS_VISIBLE|WS_CAPTION|WS_THICKFRAME,100,100,300,300,hWnd,NULL,hInst,NULL);
break;

Answer 5

我主要不明白windows默认处理什么时候擦除窗口，在程序里我在子窗口WM_PAINT消息里加了一个计数器，然后移动窗口时，有的时候重画，有的时候不重画，即便重画，也不擦除任何东西，假如我在WM_MOVE里面加入WM_ERASEBACKGROUND，只是客户区被擦除。而且有的时候，两个子窗口一块重画，假如移动的窗口没有彻底移动出来，另一个窗口的标题栏说不定反而把移动的窗口覆盖了，似乎发生移动的窗口仍在下面似的。
假如最小化然后复原，一切的乱画全消失了，我就想明白最小化而后复原时，windows究竟发送了那些消息。

Answer 6

case 9999:
        hdc = GetDC(hWnd);
        TextOut(hdc,100,100,"helllow",7);
        DeleteDC(hdc);//改为ReleaseDC(hWnd, hdc);