[英]Strange behavior animating a UIView using [UIView animateKeyframesWithDuration]
我正在尝试创建一个效果,其中三个箭头从可见变为不可见。
我做了一个简单的算法,其中每个箭头都从不同的alpha值开始(如果有3个箭头,第一个将从alpha = 1开始,第二个在alpha = 0.6667,第三个在alpha = 0.3337)。 然后我开始一个关键帧动画:
然而,由于某种原因,似乎跳过了一些步骤。
一个简单的例子:
[UIView animateKeyframesWithDuration:2 delay:0 options:UIViewKeyframeAnimationOptionCalculationModeLinear | UIViewKeyframeAnimationOptionRepeat animations:^{
[UIView addKeyframeWithRelativeStartTime:0 relativeDuration:0 animations:^{
_animatedView.alpha = 0.5;
}];
[UIView addKeyframeWithRelativeStartTime:0 relativeDuration:0.5 animations:^{
_animatedView.alpha = 0;
}];
[UIView addKeyframeWithRelativeStartTime:0.5 relativeDuration:0 animations:^{
_animatedView.alpha = 1;
}];
[UIView addKeyframeWithRelativeStartTime:0.5 relativeDuration:0.5 animations:^{
_animatedView.alpha = 0.5;
}];
} completion:nil];
在这种情况下,它应该立即变为0.5,在1秒内变为0.5到0,立即变为1,在1秒内变为1到0.5。 因此,它应该进行无缝过渡,看起来视图正在出现并消失,但看起来动画会在alpha = 0.5上停留几次。
从理论上讲,效果应该与使用此关键帧动画相同:
[UIView animateKeyframesWithDuration:2 delay:0 options:UIViewKeyframeAnimationOptionCalculationModeLinear | UIViewKeyframeAnimationOptionRepeat animations:^{
[UIView addKeyframeWithRelativeStartTime:0 relativeDuration:0 animations:^{
_animatedView.alpha = 1;
}];
[UIView addKeyframeWithRelativeStartTime:0 relativeDuration:1 animations:^{
_animatedView.alpha = 0;
}];
} completion:nil];
如果您想以相同的方式为N个视图设置动画:
CGFloat count = [self.animatedViews count];
CGFloat period = 1.0f / count;
__weak NSArray *weakViews = self.animatedViews;
[UIView animateKeyframesWithDuration:2.0f delay:0 options:UIViewKeyframeAnimationOptionCalculationModeLinear | UIViewKeyframeAnimationOptionRepeat animations:^{
for (NSUInteger index = 0; index < count; ++index) {
UIView *animatedView = weakViews[index];
CGFloat startDelay = period * index;
[UIView addKeyframeWithRelativeStartTime:0 relativeDuration:0 animations:^{
animatedView.alpha = startDelay;
}];
[UIView addKeyframeWithRelativeStartTime:0.0f relativeDuration:startDelay animations:^{
animatedView.alpha = 0.0f;
}];
[UIView addKeyframeWithRelativeStartTime:startDelay relativeDuration:0.0f animations:^{
animatedView.alpha = 1.0f;
}];
[UIView addKeyframeWithRelativeStartTime:startDelay relativeDuration:(1.0f - startDelay) animations:^{
animatedView.alpha = startDelay;
}];
}
} completion:nil];
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