UIView的setNeedsDisplay方法

setNeedsDisplay
Marks the receiver’s entire bounds rectangle as needing to be redrawn.
让接收者的整个边界矩形在需要时被重画。
- (void)setNeedsDisplay
Discussion
You can use this method or the setNeedsDisplayInRect: to notify the system that your view’s contents need to be redrawn. This method makes a note of the request and returns immediately. The view is not actually redrawn
until the next drawing cycle, at which point all invalidated views are updated.

Note: If your view is backed by a
CAEAGLLayer object, this method has no effect. It is intended for use only with views that use native drawing technologies (such as UIKit and Core Graphics) to render their content.

You should use this method to request that a view be redrawn only when the content or appearance of the view change. If you simply change the geometry of the view, the view is typically not redrawn. Instead, its existing content is adjusted based
on the value in the view’s contentMode property. Redisplaying the existing content improves performance by avoiding the need to redraw content that has not changed.
Availability
Available in iOS 2.0 and later.
See Also
– drawRect:
– setNeedsDisplayInRect:
  @property contentMode
Related Sample Code
avTouch
CoreTextPageViewer
PocketCoreImage
SpeakHere
TableViewSuite
Declared In
UIView.h