UIView&CALayer

一、UIView与CALayer的关系

UIView属性持有layer，layer的代理是UIView

二、drawRect函数调用栈

1、询问UIView是否实现了CALayerDelegate的drawLayer:inContext:代理方法，如果实现了就走drawLayer:inContext:，没实现就走drawRect:

三、渲染流程

1、layer通过代理传递给UIView

四、CALayer调用流程

• 一、布局
  1、[CALayer layerSublayers]
  2、询问代理方法
  3、[UIView layoutSubViews]
  总结：如果实现了CALayerDelegate的layoutSublayersOfLayer:代理方法，就走layoutSublayersOfLayer:，没实现就走layoutSubviews

• 二、绘制
  1、[CALayer _display]
  2、[UIView drawLayer:InContext:] 走自己的代码
  3、[UIView drawRect:]
  总结：如果实现了CALayerDelegate的drawLayer:inContext:代理方法，就走drawLayer:inContext:，没实现就走drawRect:

#import "CustomView.h"

@interface CustomView ()<CALayerDelegate>

@end

@implementation CustomView

#pragma mark -- 布局
- (void)layoutSubviews {
    NSLog(@"%s",__func__);
}

//如果实现了CALayerDelegate的layoutSublayersOfLayer:代理方法，就走layoutSublayersOfLayer:，没实现就走layoutSubviews
- (void)layoutSublayersOfLayer:(CALayer *)layer {
    NSLog(@"%s",__func__);
}

#pragma mark -- 绘制
- (void)drawRect:(CGRect)rect {
    NSLog(@"%s",__func__);
}

//如果实现了CALayerDelegate的drawLayer:inContext:代理方法，就走drawLayer:inContext:，没实现就走drawRect:
- (void)drawLayer:(CALayer *)layer inContext:(CGContextRef)ctx {
    NSLog(@"%s",__func__);
}

@end

五、模拟系统UIView与CALayer

布局
1、CALayer调用- (void)layoutSublayers{}
2、判断CALayer.delegate，是否实现了layoutSublayersOfLayer:，如果实现了执行CALayer.delegate的layoutSublayersOfLayer:；如果没有实现执行CALayer父类的layoutSublayers
3、CALayer.delegate的代理是UIView，CALayer.delegate执行- (void)layoutSublayersOfLayer:(CALayer *)layer{}，
4、layoutSublayersOfLayer:中调用 - (void)layoutSubviews{}

绘制
5、CALayer调用- (void)display{}
6、[self.delegate performSelector:@selector(createContext)]，调用UIView的- (CGContextRef)createContext{}
7、[self drawInContext:context]，调用UIView的- (void)drawLayer:(CALayer *)layer inContext:(CGContextRef)ctx{}；如果UIView没有实现- (void)drawLayer:(CALayer *)layer inContext:(CGContextRef)ctx{}，那就调用UIView的- (void)drawRect:(CGRect)rect {}
8、[self.delegate displayLayer:self]，调用UIView的- (void)displayLayer:(CALayer *)layer{}
9、[self.delegate performSelector:@selector(closeContext)]，调用UIView的- (void)closeContext{}

• LGView.h

#import <UIKit/UIKit.h>

NS_ASSUME_NONNULL_BEGIN

@interface LGView : UIView

- (CGContextRef)createContext;

- (void)closeContext;

@end

NS_ASSUME_NONNULL_END

• LGView.m

#import "LGView.h"
#import "LGLayer.h"

@implementation LGView


// Only override drawRect: if you perform custom drawing.
// An empty implementation adversely affects performance during animation.
- (void)drawRect:(CGRect)rect {
    // Drawing code， 绘制的操作， BackingStore(额外的存储区域产于的) -- GPU
}

//子视图的布局
- (void)layoutSubviews{
    [super layoutSubviews];
}

+ (Class)layerClass{
    return [LGLayer class];
}

- (void)layoutSublayersOfLayer:(CALayer *)layer{
     [self layoutSubviews];
}

- (CGContextRef)createContext{
    UIGraphicsBeginImageContextWithOptions(self.bounds.size, self.layer.opaque, self.layer.contentsScale);
    CGContextRef context = UIGraphicsGetCurrentContext();
    return context;
}



- (void)layerWillDraw:(CALayer *)layer{
    //绘制的准备工作,do nontihing
}

//绘制的操作
- (void)drawLayer:(CALayer *)layer inContext:(CGContextRef)ctx{
    [[UIColor redColor] set];
       //Core Graphics
    UIBezierPath *path = [UIBezierPath bezierPathWithRect:CGRectMake(self.bounds.size.width / 2- 20, self.bounds.size.height / 2- 20, 40, 40)];
    CGContextAddPath(ctx, path.CGPath);
    CGContextFillPath(ctx);
}

//layer.contents = (位图)
- (void)displayLayer:(CALayer *)layer{
    UIImage *image = UIGraphicsGetImageFromCurrentImageContext();
    dispatch_async(dispatch_get_main_queue(), ^{
        layer.contents = (__bridge id)(image.CGImage);
    });
}

- (void)closeContext{
    UIGraphicsEndImageContext();
}

@end

• LGLayer.m

#import "LGLayer.h"

@implementation LGLayer

//前面断点调用写下的代码
- (void)layoutSublayers{
    if (self.delegate && [self.delegate respondsToSelector:@selector(layoutSublayersOfLayer:)]) {
        //UIView
        [self.delegate layoutSublayersOfLayer:self];
    }else{
        [super layoutSublayers];
    }
}


//绘制流程的发起函数
- (void)display{
    
    // Graver 实现思路

    CGContextRef context = (__bridge CGContextRef)([self.delegate performSelector:@selector(createContext)]);
    
    [self.delegate layerWillDraw:self];
    
    [self drawInContext:context];
    
    [self.delegate displayLayer:self];

    [self.delegate performSelector:@selector(closeContext)];
}

@end

六、隐式动画和显示动画

• 隐式动画
  nil:⼿手动创建并添加到视图上的CALayer或其⼦子类在属性修改时，没有获取到具体的修改⾏行行为。此时被 修改的属性会被CATransaction记录，最终在下⼀一个runloop的回调中⽣生成动画来响应本次属性修改。 由于这个过程⾮非开发者主动完成的，因此这种动画被称作隐式动画
• 显示动画
  CAAction的⼦子类:如果返回的是CAAction对象，会直接开始动画来响应图层属性的修改。⼀一般返回的对 象多为CABasicAnimation类型，对象中包装了了动画时⻓长、动画初始/结束状态、动画时间曲线等关键 信息。当CAAction对象被返回时，会⽴立刻执⾏行行动作来响应本次属性修改