思路：
方法 创建一个图层，图层要求圆形，可传参数颜色、大小
方法 给图层设置位置和整个加载动画的大小
之后给其添加动画，并且注意动画的beginTime要有间距
创建Layer
func createLayerWith(size:CGSize,color:UIColor) -> CALayer{
let layer:CAShapeLayer = CAShapeLayer()
let path:UIBezierPath = UIBezierPath()
//addArcWithCenter,就是根据中心点画圆
/**
center:CGPoint 中心点
radius:CGFloat 半径
startAngle:CGFloat 开始的弧度
endAngle:CGFloat 结束的弧度
clockwise:Bool 绘图方向 true:顺时针 false:逆时针
*/
path.addArcWithCenter(CGPointMake(size.width/2, size.height/2), radius: size.width/2, startAngle: 0, endAngle: CGFloat(2*M_PI), clockwise: false)
layer.lineWidth = 2
layer.fillColor = color.CGColor
layer.backgroundColor = nil
layer.path = path.CGPath
return layer
}
根据传入参数，角度angle也就是每个圆对于圆心的角度，size就是小圆的半径，origin加载动画中心所在的位置，containerSize加载动画的尺寸，和颜色
func createCircle(angle:CGFloat, size:CGFloat,origin:CGPoint,containerSize:CGSize,color:UIColor)->CALayer{
let radius = containerSize.width/2
let circle = createLayerWith(CGSizeMake(size, size), color: color)
let frame = CGRectMake(origin.x+radius*(cos(angle)+1)-size/2, origin.y+radius*(sin(angle)+1)-size/2, size, size)
circle.frame = frame
return circle
}
以下是设置动画的过程，创建动画组
let scaleAnimation = CAKeyframeAnimation.init(keyPath: "transform.scale")
//该属性用以制定每个子路径的时间
scaleAnimation.keyTimes = [0,0.5,1]
//关键帧点
scaleAnimation.values = [1,0.4,1]
scaleAnimation.duration = 1
let opacityAnimation = CAKeyframeAnimation.init(keyPath: "opacity")
opacityAnimation.keyTimes = [0,0.5,1]
opacityAnimation.values = [1,0.3,1]
opacityAnimation.duration = 1
let animation = CAAnimationGroup()
animation.animations = [scaleAnimation,opacityAnimation]
animation.duration = 1
animation.repeatCount = HUGE
animation.removedOnCompletion = false
for index in 0...7{
let circle = createCircle(CGFloat(M_PI_4*Double(index)), size: 10, origin: CGPointMake(50, 50), containerSize: CGSizeMake(50, 50), color: UIColor.redColor())
animation.beginTime = Double(index)*0.125
circle.addAnimation(animation, forKey: "animation")
self.view.layer.addSublayer(circle)
}
效果图：
