昨天写一个简单的画图程序，遇到一个奇怪的问题，目的是想点鼠标左键，画个以此点为中心画个椭圆，最初的代码如下：
void CE02View::OnLButtonDown(UINT nFlags, CPoint point)
{
CPaintDC dc(this);
OnPrepareDC(&dc);
if(this->m_nColor==GRAY_BRUSH)
{
this->m_nColor = WHITE_BRUSH;
}
else
{
this->m_nColor=GRAY_BRUSH;
}
this->m_rectEllipse.left=point.x/2;
this->m_rectEllipse.right = point.x+point.x/2;
this->m_rectEllipse.top = point.y+point.y/2;
this->m_rectEllipse.bottom = point.y/2;
this->OnDraw(&dc);
CView::OnLButtonDown(nFlags, point);
}
void CE02View::OnDraw(CDC* pDC)
{
CE02Doc* pDoc = GetDocument();
ASSERT_VALID(pDoc);
pDC->SelectStockObject(this->m_nColor);
pDC->Ellipse(this->m_rectEllipse);
}
并且也考虑了第一次运行时会发出WM_PAINT事件，而在OnPaint方法里会去调用OnDraw()，所以我把OnPaint重写了，让其不调用OnDraw,这样第一次运行就不会去画了。
void CE02View::OnPaint()
{
CPaintDC dc(this); // device context for painting
}
可尽管这样，点击鼠标左键还是无法画出东西来，问了下师兄，他也不熟悉VC,弄了一会儿也无功而返，今天想了下可能是DC有问题，换了个CClientDC，唉，好了，真是怪了，用CPaintDC我是想模仿这OnPaint()的代码来写，按道理说应该可以的，可为什么在OnLButtonDown里就不行呢？最后可以运行的代码如下：
void CE02View::OnLButtonDown(UINT nFlags, CPoint point)
{
CClientDC dc(this);
OnPrepareDC(&dc);
if(this->m_nColor==GRAY_BRUSH)
{
this->m_nColor = WHITE_BRUSH;
}
else
{
this->m_nColor=GRAY_BRUSH;
}
this->m_rectEllipse.left=point.x/2;
this->m_rectEllipse.right = point.x+point.x/2;
this->m_rectEllipse.top = point.y+point.y/2;
this->m_rectEllipse.bottom = point.y/2;
this->OnDraw(&dc);
CView::OnLButtonDown(nFlags, point);
}
本文转自Phinecos(洞庭散人)博客园博客，原文链接：http://www.cnblogs.com/phinecos/archive/2007/06/09/777508.html，如需转载请自行联系原作者
