uiview animation threading issue

i am using two UIView animations to move the two different balls to particular position. But the timing of collision varies. First time they collide but second time first ball come first or viceversa. Can an开发者_JAVA技巧y buddy explain how to make them collide at same point using uiview animation. is it the thread processing issue of uiview animation

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Make sure you're animating the two views in the same block, as in

 [UIView beginAnimations:nil context:nil];
      viewOne.center = CGPointMake(40,40);
      viewTwo.center = CGPointMake(80,40);
 [UIView commitAnimations];