Core Animation

第八章 Core Animation¹

8.1 Core Animation入门

Core Animation(或者叫Quartz Core)是一个Objective-C类库，内建于IOS媒体层中，是所有动画的后台支柱。
与Core Animation并不局限于二维平面，而是可以用于三维变换。
Core Animation的许多层面已经内置与UIKit的基本操作中了,如UIViewController的切换动画,UIView的属性(如透明度，位置等)都可轻松的用动画方式改变。

可以使用UIKit动画的UIView属性：

如果直接使用Core Animation需要使用

8.2 通过UIKit使用Core Animation

1. 通过动画上下文使用UIKit动画
   

    //1.设置UIView初始条件 UIView *box=[[UIView alloc]initWithFrame:CGRectMake(0, 0, 20, 20)]; //2.启动动画上下文，并配置上下文参数 [UIView beginAnimations:@"box-animation" context:nil]; [UIView setAnimationDuration:1.];     //3.对UIView属性修改     box.frame=CGRectMake(0, 0, 20, 20);     box.backgroundColor=[UIColor greenColor]; //4.提交动画 [UIView commitAnimations];

2. 通过动画代码块使用UIKit动画

    [UIView animateWithDuration:1    delay:0    options:UIViewAnimationOptionCurveLinear    animations:^(void){          box.backgroundColor = [UIColor redColor];     Core aniMation using uikit 199   box.frame = CGRectMake(50, 50, 100, 100);   box.alpha = .5;   }   completion:^(BOOL finished){    //Add additional code    NSLog(@”Animation Finished”);    }];

8.3 理解自定义Core Animation效果

1. Core Animation图层
   CALayer,每个UIView都有一个CALaer属性，作为该视图底层表达形式。
   使用CALayer的属性做成动画，有些是UIKit中没有的，如旋转的锚点、圆角半径、掩码图层、阴影。

2. 隐式动画和显式动画
   一个CALayer包含了一个表现层和模型层。模型层存储必要的图层信息。表现层用于将模型数据显示在屏幕上没没，并做了相应优化。这样做可以提升性能，比如动画是持续变化如持续旋转，就用显式动画，因为不用修改模型层。

   • 隐式动画：动画属性在模型层修改
   • 显式动画：动画属性存在于表现层，模型层未变化，所以显式动画结束之后CALayer会回到动画开始前的状态。

3. Core Animation对象：
   与UIKit动画实现的一个不同之处在于可以使用CoreAnimation类即CAAnimation，CAAnimation及其子类都是显式动画。

   • CABasicAnimation：图层基本属性，使用CAAnimationGroup加同时添加几个，组合动画。
   • CAKeyframeAnimation：图层基本属性

   • CATransition：整个图层。

       // Set up a basic animation for rotation on z axis (spinning)  CABasicAnimation *spin = [CABasicAnimation          animationWithKeyPath:@"transform.rotation.z"];  // Set the value of the spin to 2*pi, this is 1 complete rotation in radians  spin.toValue = [NSNumber numberWithDouble:M_PI*2];  // Sping for a really long time.....  spin.repeatCount = 1e100;  spin.duration = 1.5; // duration to animate a full revolution of 2*Pi radians.  [box.layer addAnimation:spin forKey:@"transform"];  //注意CAAnimation及其子类都是显式动画，所以如果要真正发生变化，需要加  //self.layer.属性=````

8.4 Core Animation示例

1. 关键帧动画
   顾名思义，定义关键步骤

    CAKeyframeAnimation *animation = [CAKeyframeAnimation animation]; //没有tovalue,而是一个数组，每个值都会被用作一个关键帧 animation.values = [NSArray arrayWithObjects:                 (id)box.layer.backgroundColor,//这是初始条件                 (id)[UIColor yellowColor].CGColor,                 (id)[UIColor greenColor].CGColor,                 (id)[UIColor blueColor].CGColor,nil]; animation.duration = 3; animation.autoreverses = YES; [box.layer addAnimation:animation forKey:@"backgroundColor"]; //注意这个key很重要     //沿着路径进行的动画 CAKeyframeAnimation *animation = [CAKeyframeAnimation animation]; CGMutablePathRef aPath = CGPathCreateMutable(); CGPathMoveToPoint(aPath,nil,20,40);        //Origin Point CGPathAddCurveToPoint(aPath,nil, 160,30,   //Control Point 1                              220,220,  //Control Point 2                              240,380); // End Point animation.rotationMode = @"auto";//设置auto会沿着路径的切线旋转 animation.path = aPath; animation.duration = 1; animation.timingFunction = [CAMediaTimingFunction                          functionWithName:kCAMediaTimingFunctionEaseIn]; [ball.layer addAnimation:animation forKey:@"position"]; CFRelease(aPath);

2. 3D旋转

    //Step 1: 创建基本的y轴旋转Create basic y-axis rotation animation CABasicAnimation *flip = [CABasicAnimation                        animationWithKeyPath:@"transform.rotation.y"]; flip.toValue = [NSNumber numberWithDouble:-M_PI]; //Step 2: 创建基本的缩放reate Basic scale animation CABasicAnimation *scale = [CABasicAnimation                         animationWithKeyPath:@"transform.scale"]; scale.toValue = [NSNumber numberWithDouble:.9]; scale.duration = .5; scale.autoreverses = YES; //Step 3: 合成动画组合Combine scale and flip into 1 animation group CAAnimationGroup *group = [CAAnimationGroup animation]; group.animations = [NSArray arrayWithObjects:flip, scale, nil]; group.timingFunction = [CAMediaTimingFunction                      functionWithName:kCAMediaTimingFunctionEaseInEaseOut]; group.duration = 1; group.fillMode = kCAFillModeForwards; group.removedOnCompletion = NO; //Step 4: 添加动画Add animation group to our layer [box.layer addAnimation:group forKey:@"flip"]; //上面的例子不是真正的3D效果，而是用大小来模拟的，需要用到CATransform3D矩阵 //Step 1: Create basic y-axis rotation animation CABasicAnimation *flip = [CABasicAnimation                        animationWithKeyPath:@"transform.rotation.y"]; flip.toValue = [NSNumber numberWithDouble:-M_PI]; flip.duration=1.5; //Step 2 CATransform3D perspective=CATransform3DIdentity; perspective.m34=-1.0/500.0;//这个值为0无透视，为1则透视点在无限远处 perspective=CATransform3DRotate(perspective, 0, 0, 1, 0); box.layer.transform=perspective; [box.layer addAnimation:flip forKey:@"flip"];

3. 例子发射器（略） 
   
   后续内容 
   

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1. 本文是iOS5核心框架的读书笔记.↩