CAReplicatorLayer

CAReplicatorLayer的目的是為了高效生成許多相似的圖層。它會繪製一個或多個圖層的子圖層，併在每個複製體上應用不同的變換。看上去演示能夠更加解釋這些，我們來寫個例子吧。

重覆圖層（Repeating Layers）

清單6.8中，我們在屏幕的中間創建了一個小白色方塊圖層，然後用CAReplicatorLayer生成十個圖層組成一個圓圈。instanceCount屬性指定了圖層需要重覆多少次。instanceTransform指定了一個CATransform3D3D變換（這種情況下，下一圖層的位移和旋轉將會移動到圓圈的下一個點）。

變換是逐步增加的，每個實例都是相對於前一實例佈局。這就是為什麼這些複製體最終不會出現在同意位置上，圖6.8是代碼運行結果。

清單6.8 用CAReplicatorLayer重覆圖層

 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

Swift 3.0 代碼

 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     }

圖6.8 用CAReplicatorLayer創建一圈圖層

註意到當圖層在重覆的時候，他們的顏色也在變化：這是用instanceBlueOffset和instanceGreenOffset屬性實現的。通過逐步減少藍色和綠色通道，我們逐漸將圖層顏色轉換成了紅色。這個複製效果看起來很酷，但是CAReplicatorLayer真正應用到實際程式上的場景比如：一個游戲中導彈的軌跡雲，或者粒子爆炸（儘管iOS 5已經引入了CAEmitterLayer，它更適合創建任意的粒子效果）。除此之外，還有一個實際應用是：反射。

反射

使用CAReplicatorLayer並應用一個負比例變換於一個複製圖層，你就可以創建指定視圖（或整個視圖層次）內容的鏡像圖片，這樣就創建了一個實時的『反射』效果。讓我們來嘗試實現這個創意：指定一個繼承於UIView的ReflectionView，它會自動產生內容的反射效果。實現這個效果的代碼很簡單（見清單6.9），實際上用ReflectionView實現這個效果會更簡單，我們只需要把ReflectionView的實例放置於Interface Builder（見圖6.9），它就會實時生成子視圖的反射，而不需要別的代碼（見圖6.10）.

清單6.9 用CAReplicatorLayer自動繪製反射

 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