类继承的Onpaint问题2

[hxj1920]

class CDrawA : public CWnd
class CDrawB : public CDrawA

void CDrawA::OnPaint()
{
CPaintDC dc(this);
int nMode = dc.SetBkMode(TRANSPARENT);
dc.TextOut(0,0,"testDrawA");
dc.SetBkMode(nMode);
}

void CDrawB::OnPaint()
{
CDrawA::OnPaint();

CPaintDC dc(this);
int nMode = dc.SetBkMode(TRANSPARENT);
dc.TextOut(50,0,"testDrawB");
dc.SetBkMode(nMode);
}

CDrawB* pdrawb = new CDrawB;
pdrawb->Create(NULL, NULL, WS_CHILD | WS_VISIBLE |WS_BORDER,
CRect(0,0,100,100), this, 11025);
pdrawb->Invalidate();

为什么只会显示testDrawA而testDrawB不显示？该如何改写，前提是不要在CDrawB中
dc.TextOut(0,0,"testDrawA");

[oldn123]

[Quote=引用 3 楼 oldn_cc_bird 的回复:]
Onpaint是消息处理函数，　如果你消息映射在B窗口里作的的话就可以，不过现在看你应该是在A窗口里作的映射，B里没作。
不过我猜你的本意思可能是想用虚函数，比如可以自己写个A类中写个vistual void OnDraw(),OnPaint中调OnDraw.父类子类的画图部分都写在OnDraw里就可以了
[/Quote].

[dinjay]

CView::OnDraw
Called by the framework to render an image of the document. The framework calls this function to perform screen display, printing, and print preview, and it passes a different device context in each case. There is no default implementation.

就是说frame处理界面的那些工作，包括显示，打印等，都在OnDraw这个函数中做处理，那你就按LS的做法，重写这个OnDraw，然后添加自己的操作就行。一定要B做处理，那就ondraw中调用B的处理函数就行了