UIView的animation动画的停止

@property (nonatomic, strong) UIView *transformedView; //被旋转的对象
@property (nonatomic, assign) CGFloat angle; //被旋转的角度

//开始动画
- (void)startAnimation {
  CGAffineTransform endAngle = CGAffineTransformMakeRotation(self.angle * (M_PI / 180.0f));

  [UIView animateWithDuration:0.1 delay:0 options:UIViewAnimationOptionCurveLinear animations:^{
    self.transformedView.transform = endAngle;
  } completion:^(BOOL finished) {
    if (finished) {
      self.angle += 10;
      [self startAnimation];
    }
  }];
}

// 结束动画，使finished变量返回Null
- (void)stopAnimation {
  [self.transformedView.layer removeAllAnimations];
}