Android中postinvalidate和validate的区别

1. Each class which is derived from the View class has the invalidate and
the postInvalidate method.
If invalidate gets called it tells the system that the current view has changed and it should be redrawn as soon as possible. As this method can only be called from your UIThread another method is needed for when you are not in the UIThread and still want
to notify the system that your View has been changed. The postInvalidate method notifies the system from a non-UIThread and the View gets redrawn in the next event loop on the UIThread as soon as possible. It is also briefly
explained in the SDK documentation.

2. 

By this method (

postInvalidate()

),
you can invalidate a 

View

 from
non-UI threads. To invalidate a 

View

 from
UI-thread use 

invalidate()

 method.

The invalidation means, that the 

View.onDraw(Canvas)

 method
will we called at some point in the future (not immediately) to redraw whole 

View

 (if
the 

View

 is
visible).

Android is redrawing 

View

s
automaticly, but sometimes is necessary to tell: "Hey, this 

View

 has
been changed, redraw it as fast as possible."

More at:

http://developer.android.com/guide/topics/ui/how-android-draws.html

http://developer.android.com/reference/android/view/View.html#invalidate%28%29