IOS 手势拖拽弹簧效果

UIPanGestureRecognizer *recognizer = [[UIPanGestureRecognizer alloc] initWithTarget:self    action:@selector(dragContentView:)];
[self.contentView addGestureRecognizer:recognizer];

- (void)dragContentView:(UIPanGestureRecognizer *)pan
{
if (pan.state == UIGestureRecognizerStateEnded || pan.state == UIGestureRecognizerStateCancelled) {
[UIView animateWithDuration:0.25 animations:^{
pan.view.transform = CGAffineTransformIdentity;
}];
}

CGPoint translation = [pan translationInView:pan.view];
pan.view.transform = CGAffineTransformMakeTranslation(translation.x * 0.2, 0);
}