CAReplicatorLayer

Posted 2020-10-09 EchoHG

CAReplicatorLayer

CAReplicatorLayer的目的是为了高效生成许多相似的图层。它会绘制一个或多个图层的子图层，并在每个复制体上应用不同的变换。看上去演示能够更加解释这些，我们来写个例子吧。

重复图层（Repeating Layers）

清单6.8中，我们在屏幕的中间创建了一个小白色方块图层，然后用CAReplicatorLayer生成十个图层组成一个圆圈。instanceCount属性指定了图层需要重复多少次。instanceTransform指定了一个CATransform3D3D变换（这种情况下，下一图层的位移和旋转将会移动到圆圈的下一个点）。

变换是逐步增加的，每个实例都是相对于前一实例布局。这就是为什么这些复制体最终不会出现在同意位置上，图6.8是代码运行结果。

清单6.8 用CAReplicatorLayer重复图层

 1 @interface ViewController ()
 2 
 3 @property (nonatomic, weak) IBOutlet UIView *containerView;
 4 
 5 @end
 6 
 7 @implementation ViewController
 8 - (void)viewDidLoad
 9 {
10     [super viewDidLoad];
11     //create a replicator layer and add it to our view
12     CAReplicatorLayer *replicator = [CAReplicatorLayer layer];
13     replicator.frame = self.containerView.bounds;
14     [self.containerView.layer addSublayer:replicator];
15 
16     //configure the replicator
17     replicator.instanceCount = 10;
18 
19     //apply a transform for each instance
20     CATransform3D transform = CATransform3DIdentity;
21     transform = CATransform3DTranslate(transform, 0, 200, 0);
22     transform = CATransform3DRotate(transform, M_PI / 5.0, 0, 0, 1);
23     transform = CATransform3DTranslate(transform, 0, -200, 0);
24     replicator.instanceTransform = transform;
25 
26     //apply a color shift for each instance
27     replicator.instanceBlueOffset = -0.1;
28     replicator.instanceGreenOffset = -0.1;
29 
30     //create a sublayer and place it inside the replicator
31     CALayer *layer = [CALayer layer];
32     layer.frame = CGRectMake(100.0f, 100.0f, 100.0f, 100.0f);
33     layer.backgroundColor = [UIColor whiteColor].CGColor;
34     [replicator addSublayer:layer];
35 }
36 @end

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Swift 3.0 代码

 1 //    CAReplicatorLayer
 2     private lazy var replicatorView: UIView! = UIView()
 3 
 4 func replicatorLayerOfView()  {
 5         self.view.addSubview(self.replicatorView)
 6         let replicator = CAReplicatorLayer()
 7         replicator.frame = CGRect(x: 0, y: 0, width: 30, height: 30)
 8         self.replicatorView.layer.addSublayer(replicator)
 9         
10         replicator.instanceCount = 10
11         
12         var transform = CATransform3DIdentity
13         transform = CATransform3DTranslate(transform, 0, 200, 0)
14         transform = CATransform3DRotate(transform, .pi / 5.0, 0, 0, 1)
15         transform = CATransform3DTranslate(transform, 0, -200, 0)
16         replicator.instanceTransform = transform
17         
18         replicator.instanceBlueOffset = -0.1
19         replicator.instanceGreenOffset = -0.1
20         
21         let layer = CALayer()
22         layer.frame = CGRect(x: 30, y: 30, width: 30, height: 30)
23         layer.backgroundColor = UIColor.white.cgColor
24         replicator.addSublayer(layer)
25         
26         self.replicatorView.snp.makeConstraints { (make) in
27             make.top.equalTo(self.gradientView)
28             make.size.equalTo(self.gradientView)
29             make.left.equalTo(self.gradientView.snp.right).inset(-10)
30         }
31         
32     }

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图6.8 用CAReplicatorLayer创建一圈图层

注意到当图层在重复的时候，他们的颜色也在变化：这是用instanceBlueOffset和instanceGreenOffset属性实现的。通过逐步减少蓝色和绿色通道，我们逐渐将图层颜色转换成了红色。这个复制效果看起来很酷，但是CAReplicatorLayer真正应用到实际程序上的场景比如：一个游戏中导弹的轨迹云，或者粒子爆炸（尽管ios 5已经引入了CAEmitterLayer，它更适合创建任意的粒子效果）。除此之外，还有一个实际应用是：反射。

 

反射

使用CAReplicatorLayer并应用一个负比例变换于一个复制图层，你就可以创建指定视图（或整个视图层次）内容的镜像图片，这样就创建了一个实时的『反射』效果。让我们来尝试实现这个创意：指定一个继承于UIView的ReflectionView，它会自动产生内容的反射效果。实现这个效果的代码很简单（见清单6.9），实际上用ReflectionView实现这个效果会更简单，我们只需要把ReflectionView的实例放置于Interface Builder（见图6.9），它就会实时生成子视图的反射，而不需要别的代码（见图6.10）.

清单6.9 用CAReplicatorLayer自动绘制反射

 1 #import "ReflectionView.h"
 2 #import 
 3 
 4 @implementation ReflectionView
 5 
 6 + (Class)layerClass
 7 {
 8     return [CAReplicatorLayer class];
 9 }
10 
11 - (void)setUp
12 {
13     //configure replicator
14     CAReplicatorLayer *layer = (CAReplicatorLayer *)self.layer;
15     layer.instanceCount = 2;
16 
17     //move reflection instance below original and flip vertically
18     CATransform3D transform = CATransform3DIdentity;
19     CGFloat verticalOffset = self.bounds.size.height + 2;
20     transform = CATransform3DTranslate(transform, 0, verticalOffset, 0);
21     transform = CATransform3DScale(transform, 1, -1, 0);
22     layer.instanceTransform = transform;
23 
24     //reduce alpha of reflection layer
25     layer.instanceAlphaOffset = -0.6;
26 }
27 
28 - (id)initWithFrame:(CGRect)frame
29 {
30     //this is called when view is created in code
31     if ((self = [super initWithFrame:frame])) {
32         [self setUp];
33     }
34     return self;
35 }
36 
37 - (void)awakeFromNib
38 {
39     //this is called when view is created from a nib
40     [self setUp];
41 }
42 @end

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