CAKeyframeAnimation手动进度

Question

我有一个UIView，它的背景层有一个CAKeyframeAnimation，其path设置为一条简单的直线路径。

我是否可以让动画“冻结”，并手动更改其进度？

例如:如果路径长度为100点，则设置进度(偏移量？)设置为0.45时，视图将沿路径移动45个点。

我记得看过一篇文章，它通过CAMediaTiming界面做了类似的事情(根据滑块的值沿路径移动视图)，但即使经过几个小时的搜索，我也找不到它。如果我以一种完全错误的方式来处理这个问题，请一定要让我知道。谢谢。

如果上面的内容不够清楚，这里有一些示例代码。

- (void)setupAnimation
{

    CAKeyFrameAnimation *animation = [CAKeyframeAnimation animationWithKeyPath:@"position"];

    UIBezierPath *path = [UIBezierPath bezierPath];
    [path moveToPoint:_label.layer.position];
    [path addLineToPoint:(CGPoint){200, 200}];
    
    animation.path = path.CGPath;
    
    animation.duration = 1;
    animation.autoreverses = NO;
    animation.removedOnCompletion = NO;
    animation.speed = 0;
    
    // _label is just a UILabel in a storyboard
    [_label.layer addAnimation:animation forKey:@"LabelPathAnimation"]; 
}

- (void)sliderDidSlide:(UISlider *)slider
{
    // move _label along _animation.path for a distance that corresponds to slider.value
}

Answer 1

这是基于Jonathan所说的，只是稍微切中要害。动画设置正确，但滑块动作方法应如下所示：

- (void)sliderDidSlide:(UISlider *)slider 
{
    // Create and configure a new CAKeyframeAnimation instance
    CAKeyframeAnimation *animation = ...;
    animation.duration = 1.0;
    animation.speed = 0;
    animation.removedOnCompletion = NO;
    animation.timeOffset = slider.value;

    // Replace the current animation with a new one having the desired timeOffset
    [_label.layer addAnimation:animation forKey:@"LabelPathAnimation"];
}

这将使标签基于timeOffset沿动画的path移动。

Answer 2

是的，您可以使用CAMediaTiming接口来实现这一点。您可以将layer的speed设置为0，然后手动设置timeOffset。简单的pause/resume方法示例：

- (void)pauseAnimation {
    CFTimeInterval pausedTime = [yourLayer convertTime:CACurrentMediaTime() fromLayer:nil];
    yourLayer.speed = 0.0;
    yourLayer.timeOffset = pausedTime;
}

- (void)resumeAnimation {

    CFTimeInterval pausedTime = [yourLaye timeOffset];
    if (pausedTime != 0) {
        yourLayer.speed = 1.0;
        yourLayer.timeOffset = 0.0;
        yourLayer.beginTime = 0.0;

        CFTimeInterval timeSincePause = [yourLayer convertTime:CACurrentMediaTime() fromLayer:nil] - pausedTime;
        yourLayer.beginTime = timeSincePause;
    }
}