无需更新路径的 CAShapeLayer 动画

Question

在给CAShapeLayer做动画的时候，是需要不断的更新layer的路径，还是只能依赖CABasicAnimation？

在下面的示例中，我设置了四个圆形路径并绘制它们。然后我想将它们动画化以消失。然而，在动画完成后，它们 spring 回到原来的路径。

    int radius =  halfWidth-30; //the radius is the distance out from the centre
    trackActive.path = [UIBezierPath bezierPathWithArcCenter:cicleCenter radius:radius startAngle:degreesToRadians(circleStart) endAngle:degreesToRadians(circleEnd) clockwise:true].CGPath;
    circleActive.path = [UIBezierPath bezierPathWithArcCenter:cicleCenter radius:radius startAngle:degreesToRadians(circleStart) endAngle:degreesToRadians(circleEnd) clockwise:true].CGPath;

    radius = halfWidth - 10;
    trackNew.path = [UIBezierPath bezierPathWithArcCenter:cicleCenter radius:radius startAngle:degreesToRadians(circleStart) endAngle:degreesToRadians(circleEnd) clockwise:true].CGPath;
    circleNew.path = [UIBezierPath bezierPathWithArcCenter:cicleCenter radius:radius startAngle:degreesToRadians(circleStart) endAngle:degreesToRadians(circleEnd) clockwise:true].CGPath;

    NSArray * layers = @[trackActive, circleActive, trackNew, circleNew];
    for (CAShapeLayer * layer in layers){

        [CATransaction begin];
        CABasicAnimation * animation = [CABasicAnimation animationWithKeyPath:@"strokeEnd"];
        animation.duration = 1.0f;
        animation.removedOnCompletion = false;
        animation.fromValue = @(1.0);
        animation.toValue = @(0.0);
        animation.timingFunction = [CAMediaTimingFunction functionWithName:kCAMediaTimingFunctionEaseInEaseOut];
        [layer addAnimation:animation forKey:@"circleAnimation"];

        [CATransaction commit];
    }

我知道我可以添加这个来设置新路径：

    [CATransaction setCompletionBlock:^{

        //set the new path
        layer.path = [UIBezierPath bezierPathWithArcCenter:cicleCenter radius:radius startAngle:degreesToRadians(circleStart) endAngle:degreesToRadians(arcEnd) clockwise:true].CGPath;

    }];

但宁愿避免不断更新路径，而是完全依赖动画层。这可能吗？

类似于：layer.path = animation.path 或 animation.updatesOriginalPath=true；可能是一厢情愿，不确定。

Answer 1

您可以在动画中设置一个标志，使其停留在最后的位置并从应该开始的地方开始，如下所示：

[animation setRemovedOnCompletion:NO];
[animation setFillMode:kCAFillModeBoth];

同时检查这个答案： What exactly does removedOnCompletion = NO do?

Answer 2

您可以简化代码并省略 spring 效果：

[CATransaction begin];
[CATransaction setAnimationDuration:1.0];
[CATransaction setAnimationTimingFunction: kCAMediaTimingFunctionEaseInEaseOut];
layer.strokeEnd = 0.0;
[CATransaction commit];

事务将为您创建并添加一个隐式动画对象。

无需更新路径的 CAShapeLayer 动画

CAShapeLayer Animation without having to update the path

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