ios - 观察 'strokeEnd'层动画事件

Question

我想在动画开始时观察 strokeEnd 键路径。但是它不起作用，我哪里出错了？

- (void)addAnimation {
    // do animation
    CABasicAnimation *drawAnimation = [CABasicAnimation animationWithKeyPath:@"strokeEnd"];
    drawAnimation.duration            = 3.f;
    drawAnimation.repeatCount         = 1.0;
    drawAnimation.fromValue = [NSNumber numberWithFloat:0.0f];
    drawAnimation.toValue   = [NSNumber numberWithFloat:0.5f];
    drawAnimation.timingFunction = [CAMediaTimingFunction functionWithName:kCAMediaTimingFunctionEaseInEaseOut];
    drawAnimation.fillMode = kCAFillModeForwards;
    drawAnimation.removedOnCompletion = NO;
    [self.progressLayer addAnimation:drawAnimation forKey:@"drawCircleAnimation"];
    [self.progressLayer addObserver:self forKeyPath:@"strokeEnd" options:NSKeyValueObservingOptionNew context:NULL]; // 监听position

}

- (void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary *)change context:(void *)context {
    NSLog(@"change:%@",change);
    // not called here...
}

Answer 1

当动画像这样“飞行”时，您无法观察到动画属性的变化。该属性实际上设置为动画开始时的结束值。然后有一个“表示层”，位于 View 的常规层之上，动画发生在该层上。

最好的办法是设置一个 CADisplayLink 计时器(一个与屏幕刷新率同步的轻量级计时器)并查询表示层上的属性因为它动画(layer.presentationLayer.strokeEnd，在你的例子中。)