CABasicAnimation关键帧动画

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