ios - 如何在 iOS UIView 动画中跟踪动画

Question

[UIView beginAnimations:nil context:NULL]; // animate the following:
gearKnob.center = startedAtPoint;
[UIView setAnimationDuration:0.3];
[UIView commitAnimations];

这是动画，它将 UIImageView (gearKnob) 从一个点移动到另一个点。问题是当对象移动时，我需要相应地更改背景，所以我需要在移动时跟踪每个 UIImageView 位置。我怎样才能追踪它的位置？有什么方法或委托(delegate)可以做到这一点吗？

Answer 1

如果您确实必须这样做，这里有一种有效的方法。诀窍是使用 CADisplayLink 计时器并从 layer.presentationLayer 读取动画属性。

@interface MyViewController ()
...
@property(nonatomic, strong) CADisplayLink *displayLink;
...
@end

@implementation MyViewController {

- (void)animateGearKnob {

   // invalidate any pending timer
   [self.displayLink invalidate];

   // create a timer that's synchronized with the refresh rate of the display
   self.displayLink = [CADisplayLink displayLinkWithTarget:self selector:@selector(updateDuringAnimation)];
   [self.displayLink addToRunLoop:[NSRunLoop currentRunLoop] forMode:NSDefaultRunLoopMode];

   // launch the animation
   [UIView animateWithDuration:0.3 delay:0 options:0 animations:^{

       gearKnob.center = startedAtPoint;

   } completion:^(BOOL finished) {

       // terminate the timer when the animation is complete
       [self.displayLink invalidate];
       self.displayLink = nil;
   }];
}

- (void)updateDuringAnimation {

    // Do something with gearKnob.layer.presentationLayer.center

}

}