-(instancetype)initWithCenter:(CGPoint)center radius:(CGFloat)radius bgColor:(UIColor *)bgColor repeatCount:(NSInteger)repeatCount {
 if (self = [super init]) {

  //設置self的frame和center
  self.backgroundColor = bgColor;
  self.frame = CGRectMake(0, 0, radius * 2, radius * 2);
  self.center = center;

  _repeatCount = repeatCount;
  //特別注意：貝塞爾曲線的radius必須為self高度的四分之一，CAShapeLayer的線寬必須為self高度的二分之一
  UIBezierPath *path = [UIBezierPath bezierPathWithArcCenter:CGPointMake(radius, radius) radius:radius / 2 startAngle:-M_PI/2 endAngle:M_PI *3 / 2 clockwise:YES];

  CAShapeLayer *maskLayer = [CAShapeLayer layer];
  maskLayer.path = path.CGPath;
  maskLayer.fillColor = [UIColor clearColor].CGColor;
  maskLayer.strokeColor = bgColor.CGColor;
  maskLayer.lineWidth = radius; //等于半徑的2倍，以圓的邊緣為中心，向圓內部伸展一個半徑，向外伸展一個半徑，所以看上去以為圓的半徑是self高度的一半。

  self.layer.mask = maskLayer;
  _maskLayer = maskLayer;
 }

 return self;
}
-(void)startAnimaiton {
 //開始執(zhí)行扇形動畫
 CABasicAnimation *strokeEndAni = [CABasicAnimation animationWithKeyPath:@"strokeEnd"];
 strokeEndAni.fromValue = @0;
 strokeEndAni.toValue = @1;
 strokeEndAni.duration = 1;
 //重復次數(shù)
 strokeEndAni.repeatCount = _repeatCount;

 [_maskLayer addAnimation:strokeEndAni forKey:@"ani"];
}

/**
初始化對象
@param center 中心
@param radius self寬度的一半
@param bgColor 背景色
@param repeatCount 動畫重復次數(shù)
@return self
*/
-(instancetype)initWithCenter:(CGPoint)center radius:(CGFloat)radius bgColor:(UIColor *)bgColor repeatCount:(NSInteger)repeatCount;
-(void)startAnimaiton;
-(void)puaseAnimation;