removeFromSuperlayer 不删除层

Question

我正在编写允许用户临时突出显示图像的一部分的代码。在我的视图类中，我使用了 touchesBegan、touchesMoved 和 touchesEnded 从屏幕上获取 UIBezierPath。我将路径添加到图层，描边路径并使用动画将图层的不透明度从 1 淡化为 0。两个 NSLog 语句确认图层已添加到子图层数组中

drawVanishingPath
{
    NSLog(@"There were %d sublayers before the path was added",[self.layer.sublayers count]);
    disappearingLayer = [[CAShapeLayer alloc] init];
    disappearingLayer.strokeColor = self.strokeColor.CGColor;
    disappearingLayer.fillColor = [UIColor clearColor].CGColor;
    disappearingLayer.lineWidth = [self.strokeSize floatValue];
    disappearingLayer.path = path.CGPath;
    [self.layer addSublayer:disappearingLayer];
    [disappearingLayer addAnimation:fadeAnimation forKey:@"opacity"];
    [fadeAnimation setValue:disappearingLayer forKey:@"parentLayer"];
    disappearingLayer.opacity = 0.0;
    NSLog(@"There are %d sublayers after adding the path",[self.layer.sublayers count]);
}

根据另一个关于堆栈溢出的问题的答案 (How to remove a layer when its animation completes?)，我为动画设置了委托并实现了 animationDidStop:finished: 如下所示。我添加了两个 NSLog 语句以确认该层已从层数组中删除。

-(void)animationDidStop:(CAAnimation *)animation finished:(BOOL)flag
{
    NSLog(@"There were %d sublayers",[self.layer.sublayers count]);
    CAShapeLayer *layer = [animation valueForKey:@"parentLayer"];
    [layer removeAllAnimations];
    [layer removeFromSuperlayer];
    NSLog(@"There are now %d sublayers",[self.layer.sublayers count]);
}

程序运行时，添加了层，层数按预期递增，但在animationDidStop:finished:中层数并没有递减。由于没有删除层，因此程序中将有许多不需要的层。这些可能会在以后引起问题。

我相信我误解了一些东西，但我不确定哪里出了问题。任何建议将不胜感激。

How to remove a layer when its animation completes?

Answer 1

你在正确的轨道上！问题是这些行：

[disappearingLayer addAnimation:fadeAnimation forKey:@"opacity"];
[fadeAnimation setValue:disappearingLayer forKey:@"parentLayer"];

它们的顺序错误！颠倒他们的顺序，一切都会好起来的。

原因：添加到图层后不能修改动画。好吧，你可以，但它没有用：动画已被复制，所以你现在修改的不是你添加的动画。

因此，您从未设置动画的 parentLayer 键。因此，在委托方法中，该键为 nil，并且没有删除任何层。

作为测试，我运行了您的代码的简化版本，它按预期工作：

- (void)drawVanishingPath {
    NSLog(@"There were %d sublayers before the path was added",[self.layer.sublayers count]);
    CAShapeLayer* disappearingLayer = [[CAShapeLayer alloc] init];
    disappearingLayer.strokeColor = [UIColor redColor].CGColor;
    disappearingLayer.fillColor = [UIColor clearColor].CGColor;
    disappearingLayer.lineWidth = 5;
    disappearingLayer.path = _path;
    [self.layer addSublayer:disappearingLayer];

    CABasicAnimation* fadeAnimation = [CABasicAnimation animationWithKeyPath:@"opacity"];
    fadeAnimation.toValue = @0;
    fadeAnimation.duration = 2;
    fadeAnimation.delegate = self;
    [fadeAnimation setValue:disappearingLayer forKey:@"parentLayer"];
    [disappearingLayer addAnimation:fadeAnimation forKey:@"opacity"];
    NSLog(@"There are %d sublayers after adding the path",[self.layer.sublayers count]);
}

-(void)animationDidStop:(CAAnimation *)animation finished:(BOOL)flag {
    NSLog(@"There were %d sublayers",[self.layer.sublayers count]);
    CAShapeLayer *layer = [animation valueForKey:@"parentLayer"];
    [layer removeAllAnimations];
    [layer removeFromSuperlayer];
    NSLog(@"There are now %d sublayers",[self.layer.sublayers count]);
}

日志如下：

2014-05-03 17:23:21.204 PathTest[5100:60b] There were 0 sublayers before the path was added
2014-05-03 17:23:21.209 PathTest[5100:60b] There are 1 sublayers after adding the path
2014-05-03 17:23:23.210 PathTest[5100:60b] There were 1 sublayers
2014-05-03 17:23:23.211 PathTest[5100:60b] There are now 0 sublayers