iOS CALayer应用详解

跟着大神一起进步，本篇博客原文地址:http://blog.csdn.net/hello_hwc?viewmode=contents

一 CALayer是什么?

Layers是绘图和动画的基础，  Layer是在3D空间中的2D平面。Layer管理的几何（例如rotate，transfrom），内容（image等），和可视属性（backgroundColor，alpha）等信息。Layer主要通过管理bitmap来维护自己的状态信息，从这一点上来说，Layer可以看作对象模型，因为他们主要用来管理数据。

Layer是基于bitmap的，它会捕获View要呈现的内容，然后cache在一个bitmap中，这个bitmap可以看作一个对象。这样每次进行操作，例如平移旋转等，只是bitmap的矩阵运算。基于Layer的动画过程如图

由于基于Layer的绘制是处理静态的Bitmap的，而bitmap的处理又是GPU所擅长的，所以它的效率要比基于View绘制的高很多，因为基于View绘制的每次都要进行drawRect的调用重新绘制。

二 Layer支持继承 支持添加新的SubLayer 支持对sublayer进行层次调整

常见的Layer子类

管理Layer内容的几个函数

addSublayer:
insertSublayer:above:
insertSublayer:atIndex:
insertSublayer:below:
removeFromSuperlayer
replaceSublayer:with:

三 直接设置UIView 的Layer

先看一个示例，然后我们列出常用的属性，最后就是找几个比较不容易理解的属性单独分析

现在Stroyboard上拖拽一个UIView。然后control＋drag出一个IBOutlet，命名为containView

@property (weak, nonatomic) IBOutlet UIView *containView;

在ViewDidLoad 中添加如下代码

    self.containView.layer.backgroundColor = [UIColor lightGrayColor].CGColor;//背景颜色 使用CGColor
    self.containView.layer.cornerRadius = 20.0;//圆角
    self.containView.layer.shadowColor = [UIColor blueColor].CGColor;//阴影颜色
    self.containView.layer.shadowOpacity = 0.8;//阴影透明度
    self.containView.layer.shadowOffset = CGSizeMake(3.0, 3.0);
    self.containView.layer.borderWidth = 2.0f;//设置边界的宽度
    self.containView.layer.borderColor = [UIColor redColor].CGColor;//边界颜色    

这样，运行后的效果

四 添加SubLayer

    CALayer *subLayer1 = [CALayer layer];
    subLayer1.frame = CGRectMake(, , , );
    subLayer1.backgroundColor = [UIColor blueColor].CGColor;
    subLayer1.anchorPoint = CGPointMake(0.5, 0.5);
    subLayer1.position = CGPointMake(, );
    [self.containView.layer addSublayer:subLayer1];

效果图如图

有可能添加SubLayer的时候，sublayer的frame范围已经超过了super Layer的frame，那么会怎么样呢？

sublayer1.position = CGPointMake(,CGRectGetMaxY(containView.bounds)-);  

但是很多时候我们并不想subLayer的范围超出super layer 这个时候可以设置这个属性

self.containView.layer.masksToBounds = YES;  

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" 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这里再添加两个常用的CALayer 的子类UIShapeLayer 和 UITextLayer的示例

CAShapeLayer *shapeLayer = [CAShapeLayer layer];
    CGMutablePathRef path = CGPathCreateMutable();
    CGPathMoveToPoint(path, nil, , );
    CGPathAddLineToPoint(path, nil, , CGRectGetHeight(_containView.frame)/);
    shapeLayer.path = path;
    shapeLayer.bounds = CGRectMake(,,5.0,CGRectGetHeight(_containView.bounds)/);
    shapeLayer.anchorPoint = CGPointMake(0.5, 0.5);
    shapeLayer.position = CGPointMake(CGRectGetMidX(_containView.bounds),CGRectGetMidY(_containView.bounds));
    shapeLayer.lineWidth = 5.0;
    shapeLayer.lineCap = kCALineCapRound;
    shapeLayer.strokeColor = [UIColor yellowColor].CGColor;
    [self.containView.layer addSublayer:shapeLayer];

    CATextLayer * textLayer = [CATextLayer layer];
    NSString * text = @"blog.csdn.net/hello_hwc";
    NSAttributedString * attributeString = [[NSAttributedString alloc] initWithString:text];
    textLayer.string = text;
    textLayer.alignmentMode = @"center";
    textLayer.fontSize = ;
    textLayer.foregroundColor = [UIColor brownColor].CGColor;
    CGRect bounds;
    bounds.origin = CGPointMake(, );
    bounds.size = attributeString.size;
    textLayer.bounds = bounds;
    textLayer.position = CGPointMake(,);
    [_containView.layer addSublayer:textLayer];

效果图如下

五 anchorPoint和position

和UIView不同，Layer主要由三个属性来设置位置（极少用Frame）：
bounds －  设置大小
anchorPoint -设置锚点（锚点对后续的layer动画有很大影响）
position －  锚点在superLayer中的位置
这样说有点抽象，我们看看以下的图就了解了

对于iOS来说，坐标系如图，archPoint（x,y）的两个值通常取0.0-1.0,默认值是（0.5，0.5）这里的值可以看作所占用x的比例，比如默认的0.5，0.5就是在x的中间和y的中间。

而position则是AnchorPoint在super layer中的位置
如下图

六 layer 显示图片

CALayer * imageLayer = [CALayer layer];
imageLayer.bounds = CGRectMake(,,,);
imageLayer.position = CGPointMake(,);
imageLayer.contents = (id)[UIImage imageNamed:@"lichen.jpg"].CGImage;
imageLayer.contentsGravity = kCAGravityResizeAspect;
[containView.layer addSublayer:imageLayer]; 

效果图

这里,要详细讲解以下contentGravity这个属性。这个属性决定了contents如何填充。
具体分为两个方面，
方面一，位置方面
具体如图

方面二