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[操作系统]Core Animation之CABasicAnimation


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?

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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。
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1.2CAAnimation是什么呢?

CAAnimation可分为四种:

  • 1.CABasicAnimation
  • 通过设定起始点,终点,时间,动画会沿着你这设定点进行移动。可以看做特殊的CAKeyFrameAnimation
  • 2.CAKeyframeAnimation
  • Keyframe顾名思义就是关键点的frame,你可以通过设定CALayer的始点、中间关键点、终点的frame,时间,动画会沿你设定的轨迹进行移动
  • 3.CAAnimationGroup
  • Group也就是组合的意思,就是把对这个Layer的所有动画都组合起来。PS:一个layer设定了很多动画,他们都会同时执行,如何按顺序执行我到时候再讲。
  • 4.CATransition
  • 这个就是苹果帮开发者封装好的一些动画

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