problem:UIScrollView doesn't refresh...

Question

I add an UIScrollView in an UIView whose controller is UIViewController *controller1;

Now, in an function of another UIViewController, I modify the UIScrollView's frame,the code is following:

-(void)controller2Function { CGRect rect = CGRectMake (10,20, 100, 100); controller1.scrollview.frame = rect; }

after invoke the function controller2Function, scrollview still the same until I touch the screen....that is , the scroll view doesn't refresh until user touches the screen.

I have tried the setNeedsDisplay,but it doesn't work.