常用动画的原理与实现

1. CABasicAnimation  基础动画

2. CAKeyframeAnimation  关键帧动画

3. CATransition 转场动画

4. CAAnimationGroup 组动画

5. CASpringAnimation 弹性动画 （iOS9.0之后，它实现弹簧效果的动画，是CABasicAnimation的子类。）

 //假定一个3s的动画，它的状态为t0,t1,t2,t3，当没有timeOffset的时候，正常的状态序列应该为：
 //t0->t1->t2->t3
 //当设置timeOffset为1的时候状态序列就变为
 //t1->t2->t3->t0
 //同理当timeOffset为2的时候状态序列就变为：
 //t2->t3->t0->t1

 kCAMediaTimingFunctionLinear  时间曲线函数，匀速
 kCAMediaTimingFunctionEaseIn  时间曲线函数，由慢到特别快
 kCAMediaTimingFunctionEaseOut  时间曲线函数，由快到慢
 kCAMediaTimingFunctionEaseInEaseOut  时间曲线函数，由慢到快
 kCAMediaTimingFunctionDefault   系统默认

-(void)animationDidStart:(CAAnimation *)anim; 核心动画开始时执行

-(void)animationDidStop:(CAAnimation *)anim finished:(BOOL)flag; 核心动画执行结束后调用

CAPropertyAnimation *animation = [CAPropertyAnimation animationWithKeyPath:@"position.y"];
[self.view.layer addAnimation:animation forKey:@"position_y"];

注意：

随着动画的进行,在长度为duration的持续时间内,keyPath相应属性的值从fromValue渐渐地变为toValue.
如果fillMode = kCAFillModeForwards和removedOnComletion = NO;那么在动画执行完毕后,图层会保持显示动画执行后的状态,但实质上,图层的属性值还是动画执行前的初始值,并没有真正被改变.比如: CALayer的postion初始值为(0,0),CABasicAnimation的fromValue为(10,10),toValue为 (100,100),虽然动画执行完毕后图层保持在(100,100) 这个位置,实质上图层的position还是为(0,0);

CABasicAnimation *animation = [CABasicAnimation animationWithKeyPath:@"transform.rotation.z"];
animation.byValue = @(M_PI * 2);

CABasicAnimation *a1 = [CABasicAnimation animation];
a1.keyPath = @"position";
a1.toValue = [NSValue valueWithCGPoint:CGPointMake(150 + 28, 180 + 28)];
a1.duration = 0.5;
a1.fillMode = kCAFillModeForwards;
a1.removedOnCompletion = NO;
[self.view.layer addAnimation:a1 forKey:@"position"];

//设置动画属性
CAKeyframeAnimation *animation = [CAKeyframeAnimation animationWithKeyPath:@"position"];
NSValue *p1 = [NSValue valueWithCGPoint:CGPointMake(50, 150)];
NSValue *p2 = [NSValue valueWithCGPoint:CGPointMake(250, 150)];
NSValue *p3 = [NSValue valueWithCGPoint:CGPointMake(50, 550)];
NSValue *p4 = [NSValue valueWithCGPoint:CGPointMake(250, 550)];
animation.values = @[p1, p2, p3, p4];
animation.keyTimes = @[ [NSNumber numberWithFloat:0.0],
                        [NSNumber numberWithFloat:0.4],
                        [NSNumber numberWithFloat:0.8],
                        [NSNumber numberWithFloat:1.0]];

CAKeyframeAnimation * ani = [CAKeyframeAnimation animationWithKeyPath:@"position"];
CGMutablePathRef path = CGPathCreateMutable();
    CGPathAddEllipseInRect(path, NULL, CGRectMake(130, 200, 100, 100));
ani.path = path.CGPath;

CAKeyframeAnimation *animation = [CAKeyframeAnimation animationWithKeyPath:@"position"];
animation.duration = 2;
//animation.repeatCount = HUGE_VAL;
NSMutableArray *array = [NSMutableArray array];
[array addObject:[NSValue valueWithCGPoint:CGPointMake(30, 150)]];
[array addObject:[NSValue valueWithCGPoint:CGPointMake(SCREEN_WIDTH / 2.0, 70)]];
[array addObject:[NSValue valueWithCGPoint:CGPointMake(SCREEN_WIDTH - 30, 150)]];
[array addObject:[NSValue valueWithCGPoint:CGPointMake(SCREEN_WIDTH / 2.0, 300 - 50)]];
[array addObject:[NSValue valueWithCGPoint:CGPointMake(30, 150)]];
animation.values = array;
//每一个动画的时间节点位置  百分比制 0-1之间
NSMutableArray *time_array = [NSMutableArray array];
[time_array addObject:[NSNumber numberWithFloat:0.0]];
[time_array addObject:[NSNumber numberWithFloat:0.25]];
[time_array addObject:[NSNumber numberWithFloat:0.5]];
[time_array addObject:[NSNumber numberWithFloat:0.75]];
[time_array addObject:[NSNumber numberWithFloat:1.0]];
animation.keyTimes = time_array; //设置关键帧对应的时间点，范围：0-1。如果没有设置该属性，则每一帧的时间平分。

[self.imageView.layer addAnimation:animation forKey:@"CAKeyframeAnimation"];

CASpringAnimation *animation = [CASpringAnimation animationWithKeyPath:@"position.y"];
animation.fromValue = @(132);
animation.toValue = @(80);
animation.duration = animation.settlingDuration;
animation.damping = 5;
animation.initialVelocity = 0;
animation.stiffness = 500.0;
animation.mass = 1.0;
[self.imageView.layer addAnimation:animation forKey:@"CASpringAnimation"];

// 2. 向组动画中添加各种子动画
// 2.1 旋转
CABasicAnimation *anim1 = [CABasicAnimation animationWithKeyPath:@"transform.rotation.z"];
// anim1.toValue = @(M_PI * 2 * 500);
anim1.byValue = @(M_PI * 2 * 1000);

// 2.2 缩放
CABasicAnimation *anim2 = [CABasicAnimation animationWithKeyPath:@"transform.scale"];
anim2.toValue = @(0.1);

// 2.3 改变位置, 修改position
CAKeyframeAnimation *anim3 = [CAKeyframeAnimation animationWithKeyPath:@"position"];
anim3.path = [UIBezierPath bezierPathWithOvalInRect:CGRectMake(50, 100, 250, 100)].CGPath;

// 把子动画添加到组动画中
CAAnimationGroup *groupAnima = [CAAnimationGroup animation];

groupAnima.animations = @[ anim1, anim2, anim3];

groupAnima.duration = 2.0;
[self.imageView.layer addAnimation:groupAnima forKey:@"animationGroup"];

kCATransitionFade 交叉淡化过渡

kCATransitionMoveIn 新视图移到旧视图上面

kCATransitionPush 新视图把旧视图推出去

kCATransitionReveal 将旧视图移开,显示下面的新视图

kCATransitionFromRight

kCATransitionFromLeft

kCATransitionFromTop

kCATransitionFromBottom

(IBAction)didRecognizeSwipeGesture:(UISwipeGestureRecognizer *)sender {

  // 1. 创建一个转场动画对象
  CATransition *anim = [[CATransition alloc] init];
  // 设置转场动画的类型
  anim.type = @"suckEffect";
  // 设置转场动画时间
  anim.duration = 1.5;
  anim.delegate = self;
  // 判断方向
  if (sender.direction == UISwipeGestureRecognizerDirectionLeft) {
      // 设置转场动画的子类型
      anim.subtype = kCATransitionFromRight;
      // NSLog(@"left");
      self.index++;
  } else {
      // 设置转场动画的子类型
      anim.subtype = kCATransitionFromLeft;
      // NSLog(@"right");
      self.index--;
  }

  // 判断是否越界
  if (self.index > 4) {
      self.index = 0;
  }

  if (self.index < 0) {
      self.index = 4;
  }

  // 拼接图片名称
  NSString *imgName = [NSString stringWithFormat:@"%d", self.index + 1];
  // 切换图片
  self.imgViewIcon.image = [UIImage imageNamed:imgName];
  // 把转场动画添加到对应的控件上
   [self.imgViewIcon.layer addAnimation:anim forKey:@"anim1"];
}

CATransition *ani = [CATransition animation];
ani.type = @"rippleEffect"; //水滴入水振动的效果
ani.subtype = kCATransitionFromLeft;
ani.duration = 1.5;
[self.imageView.layer addAnimation:ani forKey:nil];

1.隐式属性动画的本质是这些属性的变动默认隐含了CABasicAnimation动画实现。

2.在CALayer中很少使用frame属性，因为frame本身不支持动画效果，通常使用bounds和position代替。

3.CALayer中透明度使用opacity表示而不是alpha；中心点使用position表示而不是center。

4.anchorPoint属性是图层的锚点，范围在（0-1,0-1）表示在x、y轴的比例，这个点永远可以同position（中心点）重合，当图层中心点固定后，调整anchorPoint即可达到调整图层显示位置的作用（因为它永远和position重合）

CGContextRef  ctx 图形上下文,可以将其理解为一块画布
//ctx 的备份
CGContextSaveGState(ctx);
//线的粗细
CGContextSetLineWidth(ctx, 5);

CGContextSetLineCap(ctx, kCGLineCapRound);//线条两端的样式
CGContextSetLineJoin(ctx, kCGLineJoinRound);//两线条转折相接端的样式

//ctx 的出栈  把  ctx 恢复成默认
CGContextRestoreGState(ctx);
//画笔颜色
CGContextSetRGBStrokeColor(ctx, 1, 0, 0, 1);
//两点成线
CGContextMoveToPoint(ctx, 120, 50);    //起点
CGContextAddLineToPoint(ctx, 270, 50); //画线

CGContextStrokePath(ctx); //根据ctx 线条方式绘制
CGContextFillPath(ctx); //根据ctx 填充方式绘制

画实线
CGContextMoveToPoint(ctx, 120, 50);    //起点
CGContextAddLineToPoint(ctx, 270, 50); //画线

画虚线
ctx方式：

CGFloat dash[2] = {3, 1};
CGContextSetLineWidth(ctx, 0.5);
CGContextSetLineCap(ctx, kCGLineCapRound);
CGContextSetLineDash(ctx, 0.0, dash, 2);
CGContextMoveToPoint(ctx, 120, 100);
CGContextAddLineToPoint(ctx, 270, 100);
CGContextStrokePath(ctx);

CAShapeLayer方式：

UIBezierPath *pathFour = [UIBezierPath bezierPath];
pathFour.lineWidth = 3;
[pathFour moveToPoint:CGPointMake(120, 50)];
[pathFour addLineToPoint:CGPointMake(270, 50)];
[pathFour stroke];

CAShapeLayer *layer4 = [CAShapeLayer layer];
layer4.path = pathFour.CGPath;
[layer addSublayer:layer4];
layer4.strokeColor = [[UIColor greenColor] CGColor];
layer4.fillColor = [[UIColor clearColor] CGColor];
//线型模板 这是一个NSNumber的数组，索引从1开始记，奇数位数值表示实线长度，偶数位数值表示空白长度
[layer4 setLineDashPattern:@[ @3, @1, @10, @5 ]];

画矩形
CGContextAddRect(ctx, CGRectMake(150, 50, 50, 50));

画圆、圆弧
CGContextAddArc(ctx, 60, 50, 45, 0, M_PI, 0);

画圆、画椭圆
CGContextAddEllipseInRect(ctx, CGRectMake(150, 40, 90, 50));

部分绘制
CAShapeLayer  的 strokeStart 和 strokeEnd 属性

UIBezierPath *path = [UIBezierPath bezierPath];
CAShapeLayer *layer = [CAShapeLayer layer];
[path moveToPoint:CGPointMake(50, 100)];
[path addLineToPoint:CGPointMake(200, 100)];
[path addLineToPoint:CGPointMake(200, 250)];
[path addLineToPoint:CGPointMake(50, 250)];

layer.frame = self.contentViewOne.bounds;
layer.strokeColor = [[UIColor redColor] CGColor];
layer.fillColor = [[UIColor clearColor] CGColor];
layer.lineCap = kCALineCapRound;
layer.lineJoin = kCALineJoinRound;
layer.path = [path CGPath];
layer.lineWidth = 6.0;

[self.contentViewOne.layer addSublayer:layer];

CABasicAnimation *pathAnimation = [CABasicAnimation animationWithKeyPath:@"strokeEnd"];
pathAnimation.duration = 3;
pathAnimation.fromValue = @(0.0);
pathAnimation.toValue = @(1.0);
pathAnimation.autoreverses = YES;
pathAnimation.repeatCount = HUGE;
[layer addAnimation:pathAnimation forKey:nil];

animationDuration：动画时间
animationTimingFunction：动画时间曲线
disableActions：是否关闭动画
completionBlock：动画执行完毕的回调

[CATransaction begin];
[CATransaction setAnimationDuration:2.0];
[CATransaction setAnimationTimingFunction:[CAMediaTimingFunction functionWithName:kCAMediaTimingFunctionEaseInEaseOut]];
//    [CATransaction setDisableActions:YES]; //设置为YES就关闭动画
self.subLayer.bounds = self.centerShow.layer.bounds;
[CATransaction commit];

1. frame            //大小变化：改变视图框架（frame）和边界。
2. bounds           //拉伸变化：改变视图内容的延展区域。
3. center           //居中显示
4. transform        //旋转：即任何应用到视图上的仿射变换（transform）
5. alpha            //改变透明度：改变视图的alpha值。
6. backgroundColor  //改变背景颜色
7. contentStretch   //拉伸内容

1. duration   //为动画持续的时间。 
2. animations //为动画效果的代码块。
3. completion //为动画执行完毕以后执行的代码块
4. options    //为动画执行的选项
5. delay      //为动画开始执行前等待的时间

 UIView(UIViewAnimation);
 设置动画ID 方便查询
 + (void)beginAnimations:(nullable NSString *)animationID context:(nullable void *)context;
 提交动画 执行动画
 + (void)commitAnimations;
 设置动画执行时间
 + (void)setAnimationDuration:(NSTimeInterval)duration;
 设置动画执延迟执行时间
 + (void)setAnimationDelay:(NSTimeInterval)delay;
 设置动画代理对象，当动画开始或者结束时会发消息给代理对象
 + (void)setAnimationDelegate:(nullable id)delegate;
 设置动画开始时调用的方法 执行delegate对象的selector，并且把beginAnimations:context:中传入的参数传进selector
 + (void)setAnimationWillStartSelector:(nullable SEL)selector;
 设置动画结束时调用的方法 执行delegate对象的selector，并且把beginAnimations:context:中传入的参数传进selector
 + (void)setAnimationDidStopSelector:(nullable SEL)selector;
 设置动画的开始时间，默认为now
 + (void)setAnimationStartDate:(NSDate *)startDate
 设置视图view的过渡效果, transition指定过渡类型, cache设置YES代表使用视图缓存，性能较好
 + (void)setAnimationTransition:(UIViewAnimationTransition)transition forView:(UIView *)view cache:(BOOL)cache
 设置是否自动恢复执行 YES,代表动画每次重复执行的效果会跟上一次相反
 + (void)setAnimationRepeatAutoreverses:(BOOL)repeatAutoreverses
 设置动画的重复次数
 + (void)setAnimationRepeatCount:(float)repeatCount
 设置动画执行效果
 + (void)setAnimationCurve:(UIViewAnimationCurve)curve
 设置动画是否生效
 + (void)setAnimationsEnabled:(BOOL)enabled; 

self.animationImageView.frame = CGRectMake(0, 132, 56, 36);
[UIView beginAnimations:@"btnOne" context:nil];
[UIView setAnimationCurve:UIViewAnimationCurveEaseInOut];
[UIView setAnimationDelegate:self];
[UIView setAnimationDuration:1.0];
[UIView setAnimationDelay:0.0];
[UIView setAnimationRepeatCount:1];
[UIView setAnimationRepeatAutoreverses:YES];
[UIView setAnimationDidStopSelector:@selector(AnimationDidStop)];
[UIView setAnimationWillStartSelector:@selector(AnimationWillBegin)];
[UIView setAnimationTransition:UIViewAnimationTransitionFlipFromLeft forView:self.animationImageView cache:YES];

self.animationImageView.frame = CGRectMake(SCREEN_WIDTH - 56, 132, 56, 36);
[UIView commitAnimations];

可选动画执行效果，如进出效果等
+ (void)animateWithDuration:(NSTimeInterval)duration delay:(NSTimeInterval)delay options:(UIViewAnimationOptions)options animations:(void (^)(void))animations completion:(void (^ __nullable)(BOOL finished))completion NS_AVAILABLE_IOS(4_0);

带回调block动画，动画执行完成后进入block
+ (void)animateWithDuration:(NSTimeInterval)duration animations:(void (^)(void))animations completion:(void (^ __nullable)(BOOL finished))completion NS_AVAILABLE_IOS(4_0); // delay = 0.0, options = 0

不带回调动画
+ (void)animateWithDuration:(NSTimeInterval)duration animations:(void (^)(void))animations NS_AVAILABLE_IOS(4_0); // delay = 0.0, options = 0, completion = NULL

弹簧动画
+ (void)animateWithDuration:(NSTimeInterval)duration delay:(NSTimeInterval)delay usingSpringWithDamping:(CGFloat)dampingRatio initialSpringVelocity:(CGFloat)velocity options:(UIViewAnimationOptions)options animations:(void (^)(void))animations completion:(void (^ __nullable)(BOOL finished))completion NS_AVAILABLE_IOS(7_0);

view的转场动画
+ (void)transitionWithView:(UIView *)view duration:(NSTimeInterval)duration options:(UIViewAnimationOptions)options animations:(void (^ __nullable)(void))animations completion:(void (^ __nullable)(BOOL finished))completion NS_AVAILABLE_IOS(4_0);

view到另一个view的转场动画
+ (void)transitionFromView:(UIView *)fromView toView:(UIView *)toView duration:(NSTimeInterval)duration options:(UIViewAnimationOptions)options completion:(void (^ __nullable)(BOOL finished))completion NS_AVAILABLE_IOS(4_0); // toView added to fromView.superview, fromView removed from its superview

+ (void)performSystemAnimation:(UISystemAnimation)animation onViews:(NSArray<__kindof UIView *> *)views options:(UIViewAnimationOptions)options animations:(void (^ __nullable)(void))parallelAnimations completion:(void (^ __nullable)(BOOL finished))completion NS_AVAILABLE_IOS(7_0);

[UIView animateWithDuration:1.0 delay:0.0 usingSpringWithDamping:5.0 initialSpringVelocity:0 options:UIViewAnimationOptionAutoreverse animations:^{

    self.animationImageView.frame = CGRectMake(SCREEN_WIDTH - 56, 132, 56, 36);

} completion:^(BOOL finished) {
    self.animationImageView.frame = CGRectMake(0, 132, 56, 36);
}];

关键帧动画
+ (void)animateKeyframesWithDuration:(NSTimeInterval)duration delay:(NSTimeInterval)delay options:(UIViewKeyframeAnimationOptions)options animations:(void (^)(void))animations completion:(void (^ __nullable)(BOOL finished))completion NS_AVAILABLE_IOS(7_0);

在上面的block中添加关键帧
+ (void)addKeyframeWithRelativeStartTime:(double)frameStartTime relativeDuration:(double)frameDuration animations:(void (^)(void))animations NS_AVAILABLE_IOS(7_0); // start time and duration are values between 0.0 and 1.0 specifying time and duration relative to the overall time of the keyframe animation

[UIView animateKeyframesWithDuration:2.0 delay:0.0 options:UIViewKeyframeAnimationOptionAutoreverse animations:^{

    [UIView addKeyframeWithRelativeStartTime:0.0 relativeDuration:0.5 animations:^{

        self.animationImageView.frame = CGRectMake(200, 132, 56, 36);
    }];

    [UIView addKeyframeWithRelativeStartTime:0.5 relativeDuration:0.5 animations:^{

        self.animationImageView.frame = CGRectMake(200, 232, 56, 36);
    }];

} completion:^(BOOL finished) {
    self.animationImageView.frame = CGRectMake(0, 132, 56, 36);
}];

//定义转场动画时间
- (NSTimeInterval)transitionDuration:(nullable id<UIViewControllerContextTransitioning>)transitionContext
//定义转场动画效果
- (void)animateTransition:(id<UIViewControllerContextTransitioning>)transitionContext 

//这里返回的就是navigationController push 要使用的动画效果
- (id<UIViewControllerAnimatedTransitioning>)navigationController:(UINavigationController *)navigationController animationControllerForOperation:(UINavigationControllerOperation)operation fromViewController:(UIViewController *)fromVC toViewController:(UIViewController *)toVC
{
  //在这里把 TransitionOneManager 实现的动画效果返回回去
}

self.navigationController.delegate = vc;
[self.navigationController pushViewController:vc animated:YES];

UIGravityBehavior：重力行为
UICollisionBehavior：碰撞行为
UIAttachmentBehavior：附着行为
UISnapBehavior：吸附行为
UIPushBehavior：推行为
UIDynamicItemBehavior：动力学元素行为

_animator = [[UIDynamicAnimator alloc] initWithReferenceView:self.view]; //refrerence表示 self.view内都算仿真器范围

[[UIGravityBehavior alloc] initWithItems:@[ boxView ]];
[_animator addBehavior:_gravity];

_collision = [[UICollisionBehavior alloc] initWithItems:@[ _behaviorView, _behaviorViewTwo ]];
_collision.translatesReferenceBoundsIntoBoundary = YES; //边界检测
[_animator addBehavior:_collision];

1、iOS设备的屏幕刷新频率是固定的，CADisplayLink在正常情况下会在每次刷新结束都被调用，精确度相当高。
NSTimer的精确度就显得低了点，比如NSTimer的触发时间到的时候，runloop如果在阻塞状态，触发时间就会推迟到下一个runloop周期。并且 NSTimer新增了tolerance属性，让用户可以设置可以容忍的触发的时间的延迟范围。

2、CADisplayLink使用场合相对专一，适合做UI的不停重绘，比如自定义动画引擎或者视频播放的渲染。NSTimer的使用范围要广泛的多，各种需要单次或者循环定时处理的任务都可以使用。在UI相关的动画或者显示内容使用 CADisplayLink比起用NSTimer的好处就是我们不需要在格外关心屏幕的刷新频率了，因为它本身就是跟屏幕刷新同步的。

self.displayLink = [CADisplayLink displayLinkWithTarget:self selector:@selector(animationMethod)];
self.displayLink.frameInterval = 30;
[self.displayLink addToRunLoop:[NSRunLoop mainRunLoop] forMode:NSDefaultRunLoopMode];

animationMethod 完成对应的动画操作

_snowEmitter = [CAEmitterLayer layer];

_snowEmitter.emitterPosition = CGPointMake(self.view.bounds.size.width / 2.0, -30);
_snowEmitter.emitterSize = CGSizeMake(self.view.bounds.size.width * 2.0, 0.0);
_snowEmitter.emitterShape = kCAEmitterLayerLine;
_snowEmitter.emitterMode = kCAEmitterLayerOutline;

CAEmitterCell *snowflake = [CAEmitterCell emitterCell];

snowflake.birthRate = 1.0;
snowflake.lifetime = 120.0;
snowflake.velocity = -10;
snowflake.velocityRange = 10;
snowflake.yAcceleration = 2;
snowflake.emissionRange = 0.5 * M_PI;
snowflake.spinRange = 0.25 * M_PI;
snowflake.contents = (id)[[UIImage imageNamed:@"scream"] CGImage];
snowflake.color = [[UIColor colorWithRed:0.600 green:0.658 blue:0.743 alpha:1.000] CGColor];

_snowEmitter.shadowOpacity = 1.0;
_snowEmitter.shadowRadius = 0.0;
_snowEmitter.shadowOffset = CGSizeMake(0.0, 1.0);
_snowEmitter.shadowColor = [[UIColor whiteColor] CGColor];
_snowEmitter.emitterCells = [NSArray arrayWithObject:snowflake];
[self.view.layer insertSublayer:_snowEmitter atIndex:0];

CABasicAnimation *basicAnimation = [CABasicAnimation animationWithKeyPath:@"cornerRadius"];
basicAnimation.duration = 0.2;
[self.animationView.layer setCornerRadius:20.0f];
[self.animationView.layer addAnimation:basicAnimation forKey:@"cornerRadius"];

if (self.imageViewOne.layer.speed == 0.0) {
  CFTimeInterval pausedTime = [self.imageViewOne.layer timeOffset];
  self.imageViewOne.layer.speed = 1.0;
  self.imageViewOne.layer.timeOffset = 0.0;
  self.imageViewOne.layer.beginTime = 0.0;
  CFTimeInterval timeSincePause = [self.imageViewOne.layer convertTime:CACurrentMediaTime() fromLayer:nil] - pausedTime;
  self.imageViewOne.layer.beginTime = timeSincePause;
}else{

CFTimeInterval pausedTime = [self.imageViewOne.layer convertTime:CACurrentMediaTime() fromLayer:nil];
self.imageViewOne.layer.speed = 0.0;
self.imageViewOne.layer.timeOffset = pausedTime;
}

-(void)pauseLayer:(CALayer*)layer
{
CFTimeInterval pausedTime = [layer convertTime:CACurrentMediaTime() fromLayer:nil];
layer.speed=0.0; // 让CALayer的时间停止走动
layer.timeOffset=pausedTime; // 让CALayer的时间停留在pausedTime这个时刻
}

-(void)resumeLayer:(CALayer*)layer
{
CFTimeInterval pausedTime =layer.timeOffset;
layer.speed=1.0; // 让CALayer的时间继续行走
layer.timeOffset=0.0; // 取消上次记录的停留时刻
layer.beginTime=0.0; // 取消上次设置的时间

//计算暂停的时间(这里用CACurrentMediaTime()-pausedTime也是一样的)
CFTimeInterval timeSincePause = [layer convertTime:CACurrentMediaTime() fromLayer:nil] - pausedTime;
//设置相对于父坐标系的开始时间(往后退timeSincePause)
layer.beginTime = timeSincePause;
}

CALayer *imageViewLayer = cell.imageView.layer;
imageViewLayer.shadowColor = [UIColor blackColor].CGColor;
imageViewLayer.shadowOpacity = 1.0;
imageViewLayer.shadowRadius = 2.0;
imageViewLayer.shadowOffset = CGSizeMake(1.0, 1.0);

imageViewLayer.shadowPath = CGPathCreateWithRect(imageRect, NULL);

CALayer *imageViewLayer = cell.imageView.layer;
imageViewLayer.cornerRadius = imageHeight / 2.0;
imageViewLayer.masksToBounds = YES;