ios - UILabel 的图层在动画时不更新颜色

Question

我正在使用 CATransition 为 UILabel 设置动画以“蒸发”出屏幕。
我希望标签文本变为绿色，并移出屏幕。

以下代码可以很好地“蒸发”标签，但在设置动画之前不会改变其颜色:

CATransition *transition = [CATransition animation];
transition.beginTime = CACurrentMediaTime();
transition.duration = 0.4;
transition.timingFunction = [CAMediaTimingFunction functionWithName:kCAMediaTimingFunctionDefault];
transition.type = kCATransitionPush;
transition.subtype = kCATransitionFromTop;

[self.displayLabel.layer addAnimation:transition forKey:@"evaporate"];

self.displayLabel.textColor = [self greenColor];
self.displayLabel.text = @" ";

在标签上调用 setNeedsDisplay 无效。
无法使用 CABasicAnimation，因为标签文本正在更改。

我做错了什么，我该如何解决？

Answer 1

你基本上想要嵌套动画，或者在某种意义上，寻找一个完成 block 类型的东西。
我能想到的最接近的实现方式是使用 CATransition 委托(delegate)

示例:

-(IBAction)btnTest:(UIButton *)sender
{
    //[1] Animate text color change

    CATransition *animation = [CATransition animation];
    [animation setDelegate:self]; //important
    [animation setRemovedOnCompletion:YES]; //better to remove the animation
    [animation setBeginTime:CACurrentMediaTime()]; //not really needed
    [animation setDuration:0.4];
    [animation setTimingFunction:[CAMediaTimingFunction functionWithName:kCAMediaTimingFunctionDefault]];
    [animation setType:kCATransitionFade];

    //you can specify any key name or keep it nil. doesn't make a difference
    [self.displayLabel.layer addAnimation:animation forKey:@"changeTextColor"];
    [self.displayLabel setTextColor:[UIColor greenColor]];
}

---

#pragma mark - CATransition Delegate
-(void)animationDidStop:(CAAnimation *)anim finished:(BOOL)flag
{
    //[2] Animate text sublayer

    /*
     The following CATransition should not set a delegate
     otherwise this animation will loop continously
    */

    CATransition *animation = [CATransition animation];
    [animation setRemovedOnCompletion:YES]; //better to remove the animation
    [animation setBeginTime:CACurrentMediaTime()]; //not really needed
    [animation setDuration:0.4];
    [animation setTimingFunction:[CAMediaTimingFunction functionWithName:kCAMediaTimingFunctionDefault]];
    [animation setType:kCATransitionPush];
    [animation setSubtype:kCATransitionFromTop];

    //you can specify any key name or keep it nil. doesn't make a difference
    [self.displayLabel.layer addAnimation:animation forKey:@"changeText"];
    [self.displayLabel setText:@" "];
}