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;

这实际上将动画从一端到另一端的图层绘制。问题是一旦动画完成，strokeEnd 属性会重置回 0（最初设置的位置）。如何使最终值“坚持”？

我试图在 animationDidStop 委托方法中改变它。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。我也玩过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 是可隐式动画的（这样那条线本身就会产生动画），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，另一个答案的kCAFillModeForwards 也是如此。两者都是基于对 Core Animation 工作原理的误解。