typedef NS_ENUM(NSInteger,DotDitection) 
{ 
  DotDitectionLeft = -1, 
  DotDitectionRight = 1, 
}; 
@interface XLDot : UIView 
//移动方向 就两种 左、右 
@property (nonatomic,assign) DotDitection direction; 
//字体颜色 
@property (nonatomic,strong) UIColor *textColor; 
@end 

//初始化存放豆豆的的容器 
_dotContainer = [[UIView alloc] initWithFrame:CGRectMake(0, 0, 320, 200)]; 
_dotContainer.center = self.center; 
[self addSubview:_dotContainer]; 
XLDot *dot = [[XLDot alloc] initWithFrame:CGRectMake(0, 0, [self dotWidth],[self dotWidth])]; 
dot.backgroundColor = [UIColor redColor]; 
dot.direction = DotDitectionRight; 
[_dotContainer addSubview:dot]; 

_link = [CADisplayLink displayLinkWithTarget:self selector:@selector(reloadView)]; 
[_link addToRunLoop:[NSRunLoop mainRunLoop] forMode:NSRunLoopCommonModes]; 

//刷新UI 
-(void)reloadView 
{ 
  XLDot *dot1 = _dots.firstObject; 
  //改变移动方向、约束移动范围 
  //移动到右边距时 
  if (dot1.center.x >= _dotContainer.bounds.size.width - [self dotWidth]/2.0f) { 
    CGPoint center = dot1.center; 
    center.x = _dotContainer.bounds.size.width - [self dotWidth]/2.0f; 
    dot1.center = center; 
    dot1.direction = DotDitectionLeft; 
    [_dotContainer bringSubviewToFront:dot1]; 
  } 
  //移动到左边距时 
  if (dot1.center.x <= [self dotWidth]/2.0f) { 
    dot1.center = CGPointMake([self dotWidth]/2.0f, dot1.center.y); 
    dot1.direction = DotDitectionRight; 
    [_dotContainer sendSubviewToBack:dot1]; 
  } 
  //更新第一个豆的位置 
  CGPoint center1 = dot1.center; 
  center1.x += dot1.direction * [self speed]; 
  dot1.center = center1; 
} 

//显示放大、缩小动画 
-(void)showAnimationsOfDot:(XLDot*)dot 
{ 
  CGFloat apart = dot.center.x - _dotContainer.bounds.size.width/2.0f; 
  //最大距离 
  CGFloat maxAppart = (_dotContainer.bounds.size.width - [self dotWidth])/2.0f; 
  //移动距离和最大距离的比例 
  CGFloat appartScale = apart/maxAppart; 
  //获取比例对应余弦曲线的Y值 
  CGFloat transfomscale = cos(appartScale * M_PI/2.0); 
  //向右移动则 中间变大 两边变小 
  if (dot.direction == DotDitectionLeft) { 
    dot.transform = CGAffineTransformMakeScale(1 + transfomscale/4.0f, 1 + transfomscale/4.0f); 
    //向左移动则 中间变小 两边变大 
  }else if (dot.direction == DotDitectionRight){ 
    dot.transform = CGAffineTransformMakeScale(1 - transfomscale/4.0f,1 - transfomscale/4.0f); 
  } 
} 

CGFloat apart = dot1.center.x - _dotContainer.bounds.size.width/2.0f; 
CGPoint center2 = dot2.center; 
center2.x = _dotContainer.bounds.size.width/2.0f - apart; 
dot2.center = center2;