关于画笔的一点问题，跟大家讨论讨论，欢迎交流。

[yiruirui0507]

目的：我想让25个矩形用默认黑色画笔，而让中间的差号用红色
第一种情况：
hpen=CreatePen(PS_SOLID,2,RGB(255,0,0));
SelectObject(hdc,hpen);
DeleteObject(hpen);
SelectObject(hdc,GetStockObject(BLACK_PEN));
理论上并没有发现问题，建一个画笔，选进DC，然后画线，之后删除此画笔，再把黑色画笔选进去DC，为什么就没达到效果呢？
代码：

#include <windows.h>
#define DIVISIONS 5
LRESULT CALLBACK WndProc (HWND, UINT, WPARAM, LPARAM) ;
int WINAPI WinMain (HINSTANCE hInstance, HINSTANCE hPrevInstance,
                    PSTR szCmdLine, int iCmdShow)
{
     static TCHAR szAppName [] = TEXT ("RECT") ;
     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 ("RECT TEST"), 
                          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 ;
}
     static int     cxClient, cyClient;
         static BOOL state[DIVISIONS][DIVISIONS];
LRESULT CALLBACK WndProc (HWND hwnd, UINT message, WPARAM wParam, LPARAM lParam)
{

     HDC            hdc;
         HPEN hpen;
     PAINTSTRUCT    ps ;
         RECT     rect;
         int i,j;
         int x,y;

         TCHAR szAppName[]="RECTANGLE";
     
     switch (message)
     {
     case WM_CREATE:

          return 0 ;


     case WM_SIZE:
          cxClient = LOWORD (lParam)/DIVISIONS ;
          cyClient = HIWORD (lParam)/DIVISIONS ;
          return 0 ;
         case WM_LBUTTONDOWN:
                        x=LOWORD(lParam);
                        y=HIWORD(lParam);
                        i=j=0;
                        while(!(x<i*cxClient))
                        {
                                ++i;
                        }
                        while(!(y<j*cyClient))
                        {
                                ++j;
                        }
                        if(state[i-1][j-1]==TRUE)
                        {
                                state[i-1][j-1]=FALSE;
                        }
                        else
                        {
                                state[i-1][j-1]=TRUE;
                        }
                        InvalidateRect(hwnd,NULL,TRUE);
                        return 0;
     case WM_PAINT:
                 hdc=BeginPaint(hwnd,&ps);
                 GetClientRect(hwnd,&rect);
                 hpen=CreatePen(PS_SOLID,2,RGB(255,0,0));
                
                for(j=0;j<DIVISIONS;j++)
                        for(i=0;i<DIVISIONS;i++)
                        {
                                Rectangle(hdc,i*cxClient,j*cyClient,(i+1)*cxClient,(j+1)*cyClient);
                                if(state[i][j])
                                {
                                         SelectObject(hdc,hpen);
                                        MoveToEx(hdc,i*cxClient,j*cyClient,NULL);
                                        LineTo(hdc,(i+1)*cxClient,(j+1)*cyClient);
                                                MoveToEx(hdc,i*cxClient,(j+1)*cyClient,NULL);
                                        LineTo(hdc,(i+1)*cxClient,j*cyClient);
                                        DeleteObject(hpen);
                                        SelectObject(hdc,GetStockObject(BLACK_PEN));
                                                 
                                }
                        }
                 EndPaint(hwnd,&ps);

          return 0 ;

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

情况2
如果换成下面这样：

 if(state[i][j])

                                {

                                         hpen=(HPEN)SelectObject(hdc,CreatePen(PS_SOLID,2,RGB(255,0,0)));

                                        MoveToEx(hdc,i*cxClient,j*cyClient,NULL);

                                        LineTo(hdc,(i+1)*cxClient,(j+1)*cyClient);

                                                MoveToEx(hdc,i*cxClient,(j+1)*cyClient,NULL);

                                        LineTo(hdc,(i+1)*cxClient,j*cyClient);

                                        DeleteObject(SelectObject(hdc,hpen));

                                        //SelectObject(hdc,GetStockObject(BLACK_PEN));

                                                 

                                }

倒是就没问题了。但是始终没发现情况1中为什么不可以满足要求？3Q!

[yiruirui0507]

知道错误的原因了，情况一的 DeleteObject(hpen); 放错位置了，悲剧。放到ENDPAINT上面就行了。

没人回帖？谁回分数就是谁的啊，呵呵。

[schlafenhamster]

要还原：
oldPen=SelectObject(hdc,hpen);
SelectObject(hdc,oldpen);
这时才能删除！
DeleteObject(hpen);