UIKit Dynamics doesn't allow me to animate a UIView's centre

Question

I have a UIView which is attached to a UICollisionBehavior. I'm trying to animate its center when a new location is tapped on the screen, but it appears using this block of code is not the way to do it:

    [UIView animateWithDuration:0.7f
                          delay:0.0f
                        options:UIViewAnimationOptionCurveEaseOut | UIViewAnimationOptionBeginFromCurrentState
                     animations:^{
                         [self.mainCharacter setCenter:location];
                     }
                     completion:nil];

Can anyone suggest a more UIKitDynamics friendly way of doing this?

Thanks.

UPDATE

So the first part of my question was similar to the one posted and a possible duplicate, however, although technically it solved the issue in the first part of this question, it does seem to interfere with how collision testing in UICollisionBehavior.

The second part of this question was to ask if there was a better way of doing this. I assumed it would be possible to accelerate a UIDynamicItem at a speed over a given time using UIPushBehavior but it seems to be constant.

Can anyone recommend how to use a UIPushBehavior to do the above?

Answer 1

In UIKit Dynamics, when you want to animate changing the center, you'd add a UISnapBehavior to your UIDynamicAnimator (removing any prior snap behavior first). For example, create a property for the UISnapBehavior, and then your tap gesture recognizer can snap it to that point (honoring your UICollisionBehavior), like so:

- (void)handleTap:(UITapGestureRecognizer *)gesture
{
    if (self.snap)
        [self.animator removeBehavior:self.snap];

    CGPoint point = [gesture locationInView:gesture.view];
    UISnapBehavior *snap = [[UISnapBehavior alloc] initWithItem:self.viewToAnimate snapToPoint:point];
    [self.animator addBehavior:snap];

    self.snap = snap;
}

You can control the "bounciness" by adjusting the damping property of the UISnapBehavior. If you don't like it rotating the view as it's snapping, you can also add a UIDynamicItemBehavior with allowsRotation set to NO.