[self liveInImage];
- (void)liveInImage {
UIView *layerV = [[UIView alloc] init];
layerV.frame = CGRectMake(20.0f, 20.0f, 200.0f, 300.0f);
layerV.backgroundColor = [UIColor blackColor];
[self.view addSubview:layerV];
/*
//contents屬性:如果你給contents賦的不是CGImage萍恕，那么你得到的圖層將是空白的
//你真正要賦值的類型應(yīng)該是CGImageRef逸嘀，它是一個指向CGImage結(jié)構(gòu)的指針。UIImage有一個CGImage屬性允粤，它返回一個"CGImageRef",如果你想把這個值直接賦值給CALayer的contents崭倘，那你將會得到一個編譯錯誤。因為CGImageRef并不是一個真正的Cocoa對象类垫，而是一個Core Foundation類型司光。
//layer.contents = (__bridge id)image.CGImage;//如果你沒有使用ARC（自動引用計數(shù)），你就不需要__bridge這部分悉患。但是残家，你干嘛不用ARC？售躁！
UIImage *image = [UIImage imageNamed:@"Meal"];
layerV.layer.contents = (__bridge id)image.CGImage;
//contentGravity:CALayer與contentMode對應(yīng)的屬性叫做contentsGravity, 但是它是一個NSString類型
//layerV.layer.contentsGravity = kCAGravityResizeAspect;
//contentsScale:屬性定義了寄宿圖的像素尺寸和視圖大小的比例,默認(rèn)情況下它是一個值為1.0的浮點數(shù).
//如果你只是單純地想放大圖層的contents圖片坞淮，你可以通過使用圖層的transform和affineTransform屬性來達(dá)到這個目的.
//UIView有一個類似功能但是非常少用到的contentScaleFactor屬性。
layerV.layer.contentsGravity = kCAGravityCenter;
layerV.layer.contentsScale = image.scale;
//maskToBounds:UIView有一個叫做clipsToBounds的屬性可以用來決定是否顯示超出邊界的內(nèi)容陪捷，CALayer對應(yīng)的屬性叫做masksToBounds
layerV.layer.masksToBounds = YES;
//contentsRect:CALayer的contentsRect屬性允許我們在圖層邊框里顯示寄宿圖的一個子域回窘。
//它使用了單位坐標(biāo)，單位坐標(biāo)指定在0到1之間市袖，是一個相對值（像素和點就是絕對值）啡直。默認(rèn)的contentsRect是{0, 0, 1, 1}
//contentsRect在app中最有趣的地方在于一個叫做image sprites（圖片拼合）的用法。
UIView *coneView = [[UIView alloc] init];
coneView.frame = CGRectMake(20.f, 20.0f, 50.0f, 50.0f);
[self.view addSubview:coneView];
[self addSpriteImage:image ContentRect:CGRectMake(0, 0, 0.5, 0.5) toLayer:coneView.layer];
UIView *shipView = [[UIView alloc] init];
shipView.frame = CGRectMake(100.0f, 30.0f, 50.0f, 50.0f);
[self.view addSubview:shipView];
[self addSpriteImage:image ContentRect:CGRectMake(0.5, 0, 0.5, 0.5) toLayer:shipView.layer];
UIView *iglooView = [[UIView alloc] init];
iglooView.frame = CGRectMake(60.0f, 100.0f, 50.0f, 50.0f);
[self.view addSubview:iglooView];
[self addSpriteImage:image ContentRect:CGRectMake(0, 0.5, 0.5, 0.5) toLayer:iglooView.layer];
UIView *anchorView = [[UIView alloc] init];
anchorView.frame = CGRectMake(120.0f, 100.0f, 50.0f, 50.0f);
[self.view addSubview:anchorView];
[self addSpriteImage:image ContentRect:CGRectMake(0.5, 0.5, 0.5, 0.5) toLayer:anchorView.layer];
//contentsCenter:contentsCenter其實是一個CGRect凌盯，它定義了一個固定的邊框和一個在圖層上可拉伸的區(qū)域付枫。contentsCenter是{0, 0, 1, 1}
UIButton *btn1 = [UIButton buttonWithType:UIButtonTypeCustom];
btn1.frame = CGRectMake(20.0f, 200.0, 200.0f, 200.0f);
[self.view addSubview:btn1];
[self addStretchableImage:image contentCenter:CGRectMake(0.0, 0.0, 0.5, 0.5) toLayer:btn1.layer];
UIButton *btn2 = [UIButton buttonWithType:UIButtonTypeCustom];
btn2.frame = CGRectMake(120.0f, 400.0, 200.0f, 200.0f);
[self.view addSubview:btn2];
[self addStretchableImage:image contentCenter:CGRectMake(0.25, 0.25, 0.5, 0.5) toLayer:btn2.layer];
*/
//Custome Drawing
//可以直接用Core Graphics直接繪制寄宿圖。能夠通過繼承UIView并實現(xiàn)-drawRect:方法來自定義繪制驰怎。
//如果UIView檢測到-drawRect: 方法被調(diào)用了阐滩，它就會為視圖分配一個寄宿圖，這個寄宿圖的像素尺寸等于視圖大小乘以 contentsScale的值县忌。
//-drawRect:方法里面的代碼利用Core Graphics去繪制一個寄宿圖掂榔，然后內(nèi)容就會被緩存起來直到它需要被更新
//CALayer有一個可選的delegate屬性，實現(xiàn)了CALayerDelegate協(xié)議症杏，當(dāng)CALayer需要一個內(nèi)容特定的信息時装获，就會從協(xié)議中請求。
//當(dāng)需要被重繪時厉颤，CALayer會請求它的代理給他一個寄宿圖來顯示穴豫。它通過調(diào)用下面這個方法做到的:
//(void)displayLayer:(CALayerCALayer *)layer;
//如果代理不實現(xiàn)-displayLayer:方法，CALayer就會轉(zhuǎn)而嘗試調(diào)用下面這個方法：
//- (void)drawLayer:(CALayer *)layer inContext:(CGContextRef)ctx;
//在調(diào)用這個方法之前，CALayer創(chuàng)建了一個合適尺寸的空寄宿圖（尺寸由bounds和contentsScale決定）和一個Core Graphics的繪制上下文環(huán)境精肃，為繪制寄宿圖做準(zhǔn)備秤涩，他作為ctx參數(shù)傳入。
//create sublayer
CALayer *blueLayer = [CALayer layer];
blueLayer.frame = CGRectMake(50.f, 50.0f, 100.0f, 100.0f);
blueLayer.backgroundColor = [[UIColor blueColor] CGColor];
//set controller as layer delegate
blueLayer.delegate = self;
//ensure that layer backing image uses correct scale
blueLayer.contentsScale = [UIScreen mainScreen].scale;
//add layer to our view
[layerV.layer addSublayer:blueLayer];
//force layer to redraw
[blueLayer display];
}
- (void)addSpriteImage:(UIImage *)image ContentRect:(CGRect )rect toLayer:(CALayer *)layer {
layer.contents = (__bridge id)image.CGImage;
layer.contentsGravity = kCAGravityResizeAspect;
layer.contentsRect = rect;
}
- (void)addStretchableImage:(UIImage *)image contentCenter:(CGRect )rect toLayer:(CALayer *)layer {
layer.contents = (__bridge id)image.CGImage;
layer.contentsCenter = rect;
}
#pragma mark CALayerDelegate
/*
- (void)drawLayer:(CALayer *)layer inContext:(CGContextRef)ctx {
//draw a thick red circle
CGContextSetLineWidth(ctx, 10.0f);
CGContextSetStrokeColorWithColor(ctx, [UIColor redColor].CGColor);
CGContextStrokeEllipseInRect(ctx, layer.bounds);
}
*/
