Question

WM_PAINT消息触发问题

程序本来是想实现鼠标单击改变背景颜色。可是，程序运行时，为什么没有任何消息触发，背景颜色就一直不断的改变了？WM_PAINT怎么被触发的
#include <windows.h>
#include <stdlib.h>

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

int WINAPI WinMain (HINSTANCE hInstance, HINSTANCE hPrevInstance,
PSTR szCmdLine, int iCmdShow)
{
static TCHAR szAppName[] = TEXT ("SetBackgroundColor") ;
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 ("注册失败!"),
szAppName, MB_ICONERROR) ;
return 0 ;
}

hwnd = CreateWindow (szAppName, TEXT ("SetBackgroundColor"),
WS_OVERLAPPEDWINDOW,
CW_USEDEFAULT, CW_USEDEFAULT,
CW_USEDEFAULT, CW_USEDEFAULT,
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 iMsg, WPARAM wParam, LPARAM lParam)
{
static RECT r;
HDC hdc;
HBRUSH hBrush;
switch (iMsg)
{
case WM_PAINT:
hBrush = CreateSolidBrush(RGB(rand()%256,rand()%256,rand()%256));
hdc=GetDC(hwnd);
FillRect (hdc, &r, hBrush) ;
ReleaseDC (hwnd, hdc) ;
DeleteObject (hBrush) ;
return 0;

case WM_SIZE:
GetClientRect(hwnd,&r);
return 0;

case WM_LBUTTONDOWN:
InvalidateRect(hwnd,&r,true);
return 0;

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

Answer 1

这个基础，看一下《windows程序设计》第三章吧

wm_paint是有无效区域的时候 产生的消息，所以应首先恢复该区域，才不会一直循环下去

wm_paint中应该用beginpaint与endpaint这两个api，参数是PaintStruct类型，它们的功能正是使无效区域恢复
而不是getDC与releaseDC

invalidaterect也有使区域无效的功能，可用它手动触发wm_paint事件重绘