# 手動動畫 `timeOffset`一個很有用的功能在于你可以它可以讓你手動控制動畫進程，通過設置`speed`為0，可以禁用動畫的自動播放，然后來使用`timeOffset`來來回顯示動畫序列。這可以使得運用手勢來手動控制動畫變得很簡單。 舉個簡單的例子：還是之前關門的動畫，修改代碼來用手勢控制動畫。我們給視圖添加一個`UIPanGestureRecognizer`，然后用`timeOffset`左右搖晃。 因為在動畫添加到圖層之后不能再做修改了，我們來通過調整`layer`的`timeOffset`達到同樣的效果（清單9.4）。 清單9.4 通過觸摸手勢手動控制動畫 ~~~ @interface ViewController () @property (nonatomic, weak) UIView *containerView; @property (nonatomic, strong) CALayer *doorLayer; @end @implementation ViewController - (void)viewDidLoad { [super viewDidLoad]; //add the door self.doorLayer = [CALayer layer]; self.doorLayer.frame = CGRectMake(0, 0, 128, 256); self.doorLayer.position = CGPointMake(150 - 64, 150); self.doorLayer.anchorPoint = CGPointMake(0, 0.5); self.doorLayer.contents = (__bridge id)[UIImage imageNamed:@"Door.png"].CGImage; [self.containerView.layer addSublayer:self.doorLayer]; //apply perspective transform CATransform3D perspective = CATransform3DIdentity; perspective.m34 = -1.0 / 500.0; self.containerView.layer.sublayerTransform = perspective; //add pan gesture recognizer to handle swipes UIPanGestureRecognizer *pan = [[UIPanGestureRecognizer alloc] init]; [pan addTarget:self action:@selector(pan:)]; [self.view addGestureRecognizer:pan]; //pause all layer animations self.doorLayer.speed = 0.0; //apply swinging animation (which won't play because layer is paused) CABasicAnimation *animation = [CABasicAnimation animation]; animation.keyPath = @"transform.rotation.y"; animation.toValue = @(-M_PI_2); animation.duration = 1.0; [self.doorLayer addAnimation:animation forKey:nil]; } - (void)pan:(UIPanGestureRecognizer *)pan { //get horizontal component of pan gesture CGFloat x = [pan translationInView:self.view].x; //convert from points to animation duration //using a reasonable scale factor x /= 200.0f; //update timeOffset and clamp result CFTimeInterval timeOffset = self.doorLayer.timeOffset; timeOffset = MIN(0.999, MAX(0.0, timeOffset - x)); self.doorLayer.timeOffset = timeOffset; //reset pan gesture [pan setTranslation:CGPointZero inView:self.view]; } @end ~~~ 這其實是個小詭計，也許相對于設置個動畫然后每次顯示一幀而言，用移動手勢來直接設置門的`transform`會更簡單。 在這個例子中的確是這樣，但是對于比如說關鍵這這樣更加復雜的情況，或者有多個圖層的動畫組，相對于實時計算每個圖層的屬性而言，這就顯得方便的多了。