onDraw()与onPaint()的区别是什么?

[Showshin]

呃,区别是什么?

[afx_swallow]

应该是一样用把
具体的区别请教大虾

[gniqoug]

×××××××××××
virtual void OnDraw(
CDC* pDC
) = 0;
×××××××××××

Parameters
pDC
Points to the device context to be used for rendering an image of the document.
Remarks
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.

You must override this function to display your view of the document. You can make graphic device interface (GDI) calls using the CDC object pointed to by the pDC parameter. You can select GDI resources, such as pens or fonts, into the device context before drawing and then deselect them afterwards. Often your drawing code can be device-independent; that is, it doesn't require information about what type of device is displaying the image.

To optimize drawing, call the RectVisible member function of the device context to find out whether a given rectangle will be drawn. If you need to distinguish between normal screen display and printing, call the IsPrinting member function of the device context.

The framework calls this member function when Windows or an application makes a request to repaint a portion of an application's window.
×××××××××××
afx_msg void OnPaint( );
×××××××××××

Remarks
The WM_PAINT message is sent when the UpdateWindow or RedrawWindow member function is called.

A window may receive internal paint messages as a result of calling the RedrawWindow member function with the RDW_INTERNALPAINT flag set. In this case, the window may not have an update region. An application should call the GetUpdateRect member function to determine whether the window has an update region. If GetUpdateRect returns 0, the application should not call the BeginPaint and EndPaint member functions.

It is an application's responsibility to check for any necessary internal repainting or updating by looking at its internal data structures for each WM_PAINT message because a WM_PAINT message may have been caused by both an invalid area and a call to the RedrawWindow member function with the RDW_INTERNALPAINT flag set.

An internal WM_PAINT message is sent only once by Windows. After an internal WM_PAINT message is sent to a window by the UpdateWindow member function, no further WM_PAINT messages will be sent or posted until the window is invalidated or until the RedrawWindow member function is called again with the RDW_INTERNALPAINT flag set.

[signoft]

(转载)
OnDraw()和OnPaint()兄弟
经常有朋友问雷神这样的问题：我在视图画的图象或者文字，当窗口改变后为什么不见了？OnDraw()和OnPaint()两个都是解决上面的问题，有什么不同？
雷神在这里一并解答一下吧。OnDraw()和OnPaint()好象兄弟俩，因为它们的工作类似。
至于不见了的问题简单，因为当你的窗口改变后，会产生无效区域，这个无效的区域需要重画。一般Windows回发送两个消息WM_PAINT（通知客户区有变化）和WM_NCPAINT（通知非客户区有变化）。非客户区的重画系统自己搞定了，而客户区的重画需要我们自己来完成。这就需要OnDraw()或OnPaint()来重画窗口。
OnDraw()和OnPaint()有什么区别呢？首先：我们先要明确CView类派生自CWnd类。而OnPaint()是CWnd的类成员，同时负责响应WM_PAINT消息。OnDraw()是CVIEW的成员函数，并且没有响应消息的功能。这就是为什么你用VC成的程序代码时，在视图类只有OnDraw没有OnPaint的原因。
其次：我们在第《每天跟我学MFC》3的开始部分已经说到了。要想在屏幕上绘图或显示图形，首先需要建立设备环境DC。其实DC是一个数据结构，它包含输出设备（不单指你17寸的纯屏显示器，还包括打印机之类的输出设备）的绘图属性的描述。MFC提供了CPaintDC类和CWindwoDC类来实时的响应，而CPaintDC支持重画。
当视图变得无效时（包括大小的改变，移动，被遮盖等等），Windows 将 WM_PAINT 消息发送给它。该视图的 OnPaint 处理函数通过创建 CPaintDC 类的DC对象来响应该消息并调用视图的 OnDraw 成员函数。通常我们不必编写重写的 OnPaint 处理成员函数。
///CView默认的标准的重画函数void CView::OnPaint(){ CPaintDC dc(this); OnPreparDC(&dc)； OnDraw(&dc); //调用了OnDraw}
既然OnPaint最后也要调用OnDraw,因此我们一般会在OnDraw函数中进行绘制。下面是一个典型的程序
///视图中的绘图代码首先检索指向文档的指针，然后通过DC进行绘图调用。void CMyView::OnDraw( CDC* pDC ){ CMyDoc* pDoc = GetDocument(); CString s = pDoc->GetData(); // Returns a CString CRect rect;
GetClientRect( &rect ); pDC->SetTextAlign( TA_BASELINE | TA_CENTER ); pDC->TextOut( rect.right / 2, rect.bottom / 2, s, s.GetLength() );}
最后：现在大家明白这哥俩之间的关系了吧。因此我们一般用OnPaint维护窗口的客户区（例如我们的窗口客户区加一个背景图片），用OnDraw维护视图的客户区（例如我们通过鼠标在视图中画图）。当然你也可以不按照上面规律来，只要达到目的并且没有问题，怎么干都成。
补充：我们还可以利用Invalidate(),ValidateRgn(),ValidateRect()函数强制的重画窗口，具体的请参考MSDN吧。正文完