如何用刷子，笔等在内存dc中作完图后，显示出来？

Question

想在内存dc中全部做完图后显示，但是显示不出，用dc直接作图可以，不知为什么？代码如下（在对话框OnPaint中）：
CDC memDC; //作图的内存DC
CBrush brBS;
CBrush* pTempBrush=NULL;
CRect rectBack; //控件边框 rectBack.top=0;
rectBack.left=0;
rectBack.bottom=200;
rectBack.right=800; memDC.CreateCompatibleDC(&dc); brBS.CreateSolidBrush(RGB(255,0,0));
pTempBrush = (CBrush*)memDC.SelectObject(&brBS);
memDC.FillRect(rectBack,&brBS);
memDC.SelectObject(pTempBrush);
brBS.DeleteObject(); dc.BitBlt(0,0,rectBack.right,rectBack.bottom,&memDC,0,0,SRCCOPY); memDC.DeleteDC();

Answer 1

CDC memDC; //作图的内存DC
CBrush brBS;
CBrush* pTempBrush=NULL;
CRect rectBack; //控件边框rectBack.top=0;
rectBack.left=0;
rectBack.bottom=200;
rectBack.right=800;memDC.CreateCompatibleDC(&dc);
//must create and select a bitmap in memdc
CBitmap Bitmap;
Bitmap.CreateCompatibleBitmap(&dc,rectBack.Width(),rectBack.Height());
CBitmap *pOldBitmap = (CBitmap *)memDC.SelecctObject(&Bitmap);brBS.CreateSolidBrush(RGB(255,0,0));
pTempBrush = (CBrush*)memDC.SelectObject(&brBS);
memDC.FillRect(rectBack,&brBS);
memDC.SelectObject(pTempBrush);
brBS.DeleteObject();dc.BitBlt(0,0,rectBack.right,rectBack.bottom,&memDC,0,0,SRCCOPY);
memDC.SelectObject(pOldBitmap);
memDC.DeleteDC();

Answer 2

CDC memDC; //作?的?存DC
CBrush brBS;
CBrush* pTempBrush=NULL;
CRect rectBack; //控件?框 CBitmap bmMem, *pOldBitmap; rectBack.top=0;
rectBack.left=0;
rectBack.bottom=200;
rectBack.right=800; memDC.CreateCompatibleDC(&dc);
bmMem.CreateCompatibleBitmap(&dc, rectBack.right, rectBack.bottom);
pOldBitmap = memDC.SelectObject(&bmMem); brBS.CreateSolidBrush(RGB(255,0,0));
pTempBrush = (CBrush*)memDC.SelectObject(&brBS);
memDC.FillRect(rectBack,&brBS); dc.BitBlt(0,0,rectBack.right,rectBack.bottom,&memDC,0,0,SRCCOPY); memDC.SelectObject(pTempBrush);
memDC.SelectObject(pOldBitmap); memDC.DeleteDC();