如何通过自定义渐变更改strokeColor

Question

我想为CAShapeLayer的strokeColor设置动画，但在CABasicAnimation中我有两个值（from和to）。动画是火的时候只有两种颜色支持吗？例如，一开始我有strokeColor = [UIColor blueColor].CGColor; 然后

CABasicAnimation *colorAnimation = [CABasicAnimation animationWithKeyPath:@"strokeColor"];
colorAnimation.duration            = 3.0; // "animate over 3 seconds or so.."
colorAnimation.repeatCount         = 1.0;  // Animate only once..
colorAnimation.removedOnCompletion = NO;   // Remain stroked after the animation..
colorAnimation.fillMode = kCAFillModeForwards;
colorAnimation.toValue   = (id)[UIColor redColor].CGColor;
colorAnimation.timingFunction = [CAMediaTimingFunction functionWithName:kCAMediaTimingFunctionEaseIn];

中途我有深紫色，但我需要，例如，黄色。

是否可以向CABasicAnimation添加自定义渐变？

Answer 1

我不认为您可以使用CABasicAnimation执行此操作，但您可以使用CAKeyframeAnimation为动画设置中间值：

CAKeyframeAnimation *colorAnimation = [CAKeyframeAnimation animationWithKeyPath:@"strokeColor"];
colorAnimation.values               = @[(id)[[UIColor blueColor] CGColor],
                                        (id)[[UIColor yellowColor] CGColor],
                                        (id)[[UIColor redColor] CGColor]];
colorAnimation.duration             = 3.0;  // "animate over 3 seconds or so.."
colorAnimation.repeatCount          = 1.0;  // Animate only once..
colorAnimation.removedOnCompletion  = NO;   // Remain stroked after the animation..
colorAnimation.fillMode             = kCAFillModeForwards;
colorAnimation.timingFunction       = [CAMediaTimingFunction functionWithName:kCAMediaTimingFunctionEaseIn];

如果你想要一种“跨频谱”的感觉，你可以这样做：

colorAnimation.values = @[(id)[[UIColor blueColor] CGColor],
                          (id)[[UIColor greenColor] CGColor],
                          (id)[[UIColor yellowColor] CGColor],
                          (id)[[UIColor orangeColor] CGColor],
                          (id)[[UIColor redColor] CGColor]];

或者，如果您想要更多简单的蓝色到红色，但避免使用非常暗紫色，您可以这样做：

colorAnimation.values = @[(id)[[UIColor blueColor] CGColor],
                          (id)[[UIColor colorWithRed:0.9 green:0.0 blue:0.9 alpha:1.0] CGColor],
                          (id)[[UIColor redColor] CGColor]];

很多选择。