ios - 如何使图层保持 CABasicAnimation 的最终值

Question

考虑以下动画:

CABasicAnimation *pathAnimation = [CABasicAnimation animationWithKeyPath:@"strokeEnd"];
pathAnimation.duration = 1.0;
pathAnimation.timingFunction = [CAMediaTimingFunction functionWithName:kCAMediaTimingFunctionEaseOut];
pathAnimation.fromValue = [NSNumber numberWithFloat:0.0f];
pathAnimation.toValue = [NSNumber numberWithFloat:1.0f];
pathAnimation.removedOnCompletion = NO;
pathAnimation.delegate = self;

这将从本质上使图层的绘制从一端动画到另一端。问题在于，一旦动画完成，strokeEnd 属性将重置回 0(最初设置的位置)。如何使最终值“稳定”？

我试图在 animationDidStop 委托(delegate)方法中更改它。这主要是有效的，但可能会导致 strokeEnd 在 0 处短暂闪烁，即使放在 CATransaction 中以禁用动画也是如此。我还玩过 additive 和 cumulative 属性，但无济于事。有什么建议吗？

Answer 1

您只需自己将 strokeEnd 属性设置为其最终值!像这样:

// your current code (stripped of unnecessary stuff)

CABasicAnimation *pathAnimation = [CABasicAnimation animationWithKeyPath:@"strokeEnd"];
pathAnimation.duration = 1.0;
pathAnimation.timingFunction = [CAMediaTimingFunction functionWithName:kCAMediaTimingFunctionEaseOut];
pathAnimation.fromValue = [NSNumber numberWithFloat:0.0f];
pathAnimation.toValue = [NSNumber numberWithFloat:1.0f];

// just add this to it:

theLayer.strokeEnd = 1;

// and now add the animation to theLayer

如果 strokeEnd 是隐式可动画的(以便该行本身会导致动画)，我们将首先关闭隐式动画:

[CATransaction setDisableActions:YES];
theLayer.strokeEnd = 1;

请注意，您的 pathAnimation.removedOnCompletion = NO; 是错误的，其他答案的 kCAFillModeForwards 也是错误的。两者都是基于对 Core Animation 工作原理的误解。