在iOS中，图形可分为以下几个层次：
越上层，封装程度越高，动画实现越简洁越简单，但是自由度越低；反之亦然。本文着重介绍Core Animation层的基本动画实现方案。
在iOS中，展示动画可以类比于显示生活中的“拍电影”。拍电影有三大要素：演员+剧本+开拍，概念类比如下：
演员--->CALayer，规定电影的主角是谁剧本--->CAAnimation，规定电影该怎么演，怎么走，怎么变换开拍--->AddAnimation，开始执行
一、概念介绍
1.1CALayer是什么呢？
CALayer是个与UIView很类似的概念，同样有layer,sublayer...，同样有backgroundColor、frame等相似的属性，我们可以将UIView看做一种特殊的CALayer，只不过UIView可以响应事件而已。一般来说，layer可以有两种用途，二者不互相冲突：一是对view相关属性的设置，包括圆角、阴影、边框等参数，更详细的参数请点击这里；二是实现对view的动画操控。因此对一个view进行core animation动画，本质上是对该view的.layer进行动画操纵。
1.2CAAnimation是什么呢？
CAAnimation可分为四种：
二、动手干活
实践出真知，看个例子就知道：
比如我们想实现一个类似心跳的缩放动画可以这么做，分为演员初始化、设定剧本、电影开拍三个步骤：
- (void)initScaleLayer{ //演员初始化 CALayer *scaleLayer = [[CALayer alloc] init]; scaleLayer.backgroundColor = [UIColor blueColor].CGColor; scaleLayer.frame = CGRectMake(60, 20 + kYOffset, 50, 50); scaleLayer.cornerRadius = 10; [self.view.layer addSublayer:scaleLayer]; [scaleLayer release]; //设定剧本 CABasicAnimation *scaleAnimation = [CABasicAnimation animationWithKeyPath:@"transform.scale"]; scaleAnimation.fromValue = [NSNumber numberWithFloat:1.0]; scaleAnimation.toValue = [NSNumber numberWithFloat:1.5]; scaleAnimation.autoreverses = YES; scaleAnimation.fillMode = kCAFillModeForwards; scaleAnimation.repeatCount = MAXFLOAT; scaleAnimation.duration = 0.8; //开演 [scaleLayer addAnimation:scaleAnimation forKey:@"scaleAnimation"];}
- (void)viewDidLoad { [super viewDidLoad]; // Do any additional setup after loading the view from its nib. [self initScaleLayer];}
效果请参考附图中的绿色方块(我不懂在mac下怎么录制gif图，先借用kk的图)。其他效果可以依葫芦画瓢轻松实现。想要实现不同的效果，最关键的地方在于CABasicAnimation对象的初始化方式中keyPath的设定。在iOS中有以下几种不同的keyPath，代表着不同的效果：
此外，我们还可以利用GroupAnimation实现多种动画的组合，在GroupAnimation中的各个动画类型是同时进行的。
- (void)initGroupLayer { //演员初始化 CALayer *groupLayer = [[CALayer alloc] init]; groupLayer.frame = CGRectMake(60, 340+100 + kYOffset, 50, 50); groupLayer.cornerRadius = 10; groupLayer.backgroundColor = [[UIColor purpleColor] CGColor]; [self.view.layer addSublayer:groupLayer]; [groupLayer release]; //设定剧本 CABasicAnimation *scaleAnimation = [CABasicAnimation animationWithKeyPath:@"transform.scale"]; scaleAnimation.fromValue = [NSNumber numberWithFloat:1.0]; scaleAnimation.toValue = [NSNumber numberWithFloat:1.5]; scaleAnimation.autoreverses = YES; scaleAnimation.repeatCount = MAXFLOAT; scaleAnimation.duration = 0.8; CABasicAnimation *moveAnimation = [CABasicAnimation animationWithKeyPath:@"position"]; moveAnimation.fromValue = [NSValue valueWithCGPoint:groupLayer.position]; moveAnimation.toValue = [NSValue valueWithCGPoint:CGPointMake(320 - 80, groupLayer.position.y)]; moveAnimation.autoreverses = YES; moveAnimation.repeatCount = MAXFLOAT; moveAnimation.duration = 2; CABasicAnimation *rotateAnimation = [CABasicAnimation animationWithKeyPath:@"transform.rotation.x"]; rotateAnimation.fromValue = [NSNumber numberWithFloat:0.0]; rotateAnimation.toValue = [NSNumber numberWithFloat:6.0 * M_PI]; rotateAnimation.autoreverses = YES; rotateAnimation.repeatCount = MAXFLOAT; rotateAnimation.duration = 2; CAAnimationGroup *groupAnnimation = [CAAnimationGroup animation]; groupAnnimation.duration = 2; groupAnnimation.autoreverses = YES; groupAnnimation.animations = @[moveAnimation, scaleAnimation, rotateAnimation]; groupAnnimation.repeatCount = MAXFLOAT; //开演 [groupLayer addAnimation:groupAnnimation forKey:@"groupAnnimation"]; }
- (void)viewDidLoad { [super viewDidLoad]; // Do any additional setup after loading the view from its nib. [self initGroupLayer];} 
完整的demo工程点CAAnimationDemo.zip下载
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