contents属性

CALayer的contents属性，为id类型，意味着可以是任何类型对象。中间需要做类型转换。

layer.contents = (__bridge id)image.CGImage;//这是在ARC下

例如给view1加载一张图片

UIImage *image = [UIImage imageNamed:@”p1.jpg”];

self.view1.layer.contents = (__bridge id)image.CGImage;

图片是铺满图层的，可以设置contentGravity来改变加载状况。

layer.contentsGravity = kCAGravityResizeAspect;

设置不同的

contentsGravity值将达到不同的效果。

contentScale 属性定义了寄宿图像和视图大小的比例。当用代码设置寄宿图像时，一定要设置contentScale属性

blueLayer.contentsScale = [[UIScreen mainScreen] scale];

maskToBounds

设置超出边界部分是否显示。

contentsRect 属性允许我们在视图层里面线束寄宿图像的一个子域。用于图片分割

- (void)viewDidLoad {
    [super viewDidLoad];
   UIImage *image = [UIImage imageNamed:@"p1.jpg"];
    
    //图片分割
    [self addSpriteImage:image WithContentReact:CGRectMake(0, 0, 0.5, 0.5) WithLayer:self.view1.layer];
    [self addSpriteImage:image WithContentReact:CGRectMake(0.5, 0, 0.5, 0.5) WithLayer:self.view3.layer];
    [self addSpriteImage:image WithContentReact:CGRectMake(0, 0.5, 0.5, 0.5) WithLayer:self.view2.layer];
    [self addSpriteImage:image WithContentReact:CGRectMake(0.5, 0.5, 0.5, 0.5) WithLayer:self.view4.layer];
    
}
-(void)addSpriteImage:(UIImage *)image WithContentReact:(CGRect)react WithLayer:(CALayer *)layer{
    layer.contents = (__bridge id)image.CGImage;
    layer.contentsRect =react;
    layer.contentsGravity = kCAGravityResizeAspect;
}

contentsCenter

属性用于设置图层拉伸位置，定义了一个固定的边框和一个在图层上可拉伸区域

在CALayer上面绘制。要遵守CALayerDelegate代理协议，首先会生成一个上下文用于绘制。

-(void)addSpriteImage:(UIImage *)image WithContentReact:(CGRect)react WithLayer:(CALayer *)layer在此代理中绘制

- (void)viewDidLoad {
    [super viewDidLoad];


    CALayer *blueLayer = [CALayer layer];
    blueLayer.backgroundColor = [UIColor blueColor].CGColor;
    blueLayer.frame = CGRectMake(50, 50, 100, 100);
    blueLayer.contentsScale = [[UIScreen mainScreen] scale];
    [self.view1.layer addSublayer:blueLayer];
     blueLayer.delegate = self;
    [blueLayer display];
    
}
- (void)drawLayer:(CALayer *)layer inContext:(CGContextRef)ctx{
    CGContextSetLineWidth(ctx, 10.0);
    CGContextSetStrokeColorWithColor(ctx, [UIColor redColor].CGColor);
    CGContextStrokeEllipseInRect(ctx, layer.bounds);
    
}