invalidate() and postInvalidate()

/**

* Invalidate the whole view. If the view is

visible,

* {@link #onDraw(android.graphics.Canvas)} will be

called at some point in

* the future. This must be called

from a UI thread. To call from a non-UI thread,

* call

{@link #postInvalidate()}.

*/

invalidate():This must be called from a UI thread

postInvalidate():This must be called from a non-UI

thread