# 手动动画 `timeOffset`一个很有用的功能在于你可以它可以让你手动控制动画进程，通过设置`speed`为0，可以禁用动画的自动播放，然后来使用`timeOffset`来来回显示动画序列。这可以使得运用手势来手动控制动画变得很简单。 举个简单的例子：还是之前关门的动画，修改代码来用手势控制动画。我们给视图添加一个`UIPanGestureRecognizer`，然后用`timeOffset`左右摇晃。 因为在动画添加到图层之后不能再做修改了，我们来通过调整`layer`的`timeOffset`达到同样的效果（清单9.4）。 清单9.4 通过触摸手势手动控制动画 ~~~ @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 ~~~ 这其实是个小诡计，也许相对于设置个动画然后每次显示一帧而言，用移动手势来直接设置门的`transform`会更简单。 在这个例子中的确是这样，但是对于比如说关键这这样更加复杂的情况，或者有多个图层的动画组，相对于实时计算每个图层的属性而言，这就显得方便的多了。