所谓关键帧动画，就是将Layer的属性作为KeyPath来注册，指定动画的起始帧和结束帧，然后自动计算和实现中间的过度的一种动画方式。
CABasicAnimation 基本动画
基本使用方法：
CABasicAnimation *animation = [CABasicAnimation animationWithKeyPath:@"opacity"];
animation.duration = 1;
animation.fromValue = @1;
animation.toValue = @0.f;
// 设置完动画之后一定要添加到你想要执行的Layer上，要不，动画无效
[layer addAnimation:animation forKey:@"myopacity"];
属性说明：
-
duration动画时长(秒)，默认为0，不设置的话，会快速执行完你设置的动画 -
speed执行速度，默认为1倍。如果设置了该属性，则执行时间会变为（duration/speed） -
repeatCount重复次数，默认为0，即不重复，如果需要设置成永久的话可以设置为HUGE_VALF -
autoreverses动画执行完是否执行逆动画，默认为NO -
fromValue开始值 -
toValue结束值
注：CABasicAnimation执行完动画后会回归动画开始的状态，如果想要让它变成动画执行最后的状态，设置一下两个属性。(不建议这样做，耗费资源)
animation.removedOnCompletion = NO;
animation.fillMode = kCAFillModeForwards;
最后，动画执行完成后要记得将layer上的动画删除。
[self.myview.layer removeAllAnimations];
举个🌰： 我们弄个改变Layer透明度的动画，代码见下：
CABasicAnimation *animation = [CABasicAnimation animationWithKeyPath:@"opacity"];
animation.duration = 1;
animation.repeatCount = HUGE_VALL;
animation.autoreverses = YES;
animation.fromValue = @1;
animation.toValue = @0.f;
[layer addAnimation:animation forKey:@"myopacity"];
效果如图：
1.gif
再来一个它常用的组合类型：
- (void)drawRect:(CGRect)rect {
// Drawing code
CGSize size = self.bounds.size;
UIBezierPath *path = [UIBezierPath bezierPath];
[path moveToPoint:CGPointMake(0, 0)];
[path addLineToPoint:CGPointMake(size.width, 0)];
[path addLineToPoint:CGPointMake(size.width, size.height)];
[path addLineToPoint:CGPointMake(0, size.height)];
[path closePath];
self.mylayer = [CAShapeLayer layer];
self.mylayer.frame = self.bounds;
self.mylayer.lineWidth = 5;
self.mylayer.strokeColor = [UIColor redColor].CGColor;
self.mylayer.path = path.CGPath;
[self.layer addSublayer:self.mylayer];
CABasicAnimation *pathAnimation = [CABasicAnimation animationWithKeyPath:@"strokeEnd"];
pathAnimation.duration = 1.0;
pathAnimation.repeatCount = HUGE_VALF;
pathAnimation.autoreverses = YES;
pathAnimation.fromValue = [NSNumber numberWithFloat:0.f];
pathAnimation.toValue = [NSNumber numberWithFloat:1.f];
[self.mylayer addAnimation:pathAnimation forKey:nil];
}
效果图：
2.gif
