iOS 转盘效果

//转盘效果，如果使用autolayout创建的view，会出问题，建议使用纯代码

//开始
- (void)startRotating
{
    if (self.link) return;
    
    // 1秒内刷新60次
    CADisplayLink *link = [CADisplayLink displayLinkWithTarget:self selector:@selector(update)];
    [link addToRunLoop:[NSRunLoop mainRunLoop] forMode:NSDefaultRunLoopMode];
    self.link = link;
}

//停止
- (void)stopRotating
{
    [self.link invalidate];
    self.link = nil;
}

//刷新
- (void)update
{
    self.centerWheel.transform = CGAffineTransformRotate(self.centerWheel.transform, M_PI / 500);
}