做一個無限旋轉的UIView

這幾天需要做一個無限旋轉的View，有點像下圖這樣，一個開關控制風扇啟動與停止。

在stackoverflow上找到一篇相關的討論，在所有答案中我最喜歡Nate的答案。

// an ivar for your class:
BOOL animating;

- (void) spinWithOptions: (UIViewAnimationOptions) options {
   // this spin completes 360 degrees every 2 seconds
   [UIView animateWithDuration: 0.5f
                         delay: 0.0f
                       options: options
                    animations: ^{
                       self.imageToMove.transform = CGAffineTransformRotate(imageToMove.transform, M_PI / 2);
                    }
                    completion: ^(BOOL finished) {
                       if (finished) {
                          if (animating) {
                             // if flag still set, keep spinning with constant speed
                             [self spinWithOptions: UIViewAnimationOptionCurveLinear];
                          } else if (options != UIViewAnimationOptionCurveEaseOut) {
                             // one last spin, with deceleration
                             [self spinWithOptions: UIViewAnimationOptionCurveEaseOut];
                          }
                       }
                    }];
}

- (void) startSpin {
   if (!animating) {
      animating = YES;
      [self spinWithOptions: UIViewAnimationOptionCurveEaseIn];
   }   
}

- (void) stopSpin {
    // set the flag to stop spinning after one last 90 degree increment
    animating = NO;
}