自定义Layer的两种方法

view的完整显示过程:

　　1.view.layer会准备一个Layer Graphics Context(图层类型上下文)

　　2.调用view.layer.delegate(即view)的drawLayer:inContext:并传入准备好的上下文

　　3.view的drawLayer:inContext:方法内部会调用view的drawRect:方法

　　4.view就可以在drawRect:方法中实现绘图,所有东西都会绘制到view.layer上

　　5.系统再将view.layer内容拷贝到屏幕上,完成显示

 1 //
 2 //  ViewController.m
 3 //  calayer,自定义Layer
 4 //
 5 //  Created by ys on 15/11/21.
 6 //  Copyright (c) 2015年 ys. All rights reserved.
 7 //
 8
 9 #import "ViewController.h"
10 #import "ysLayer.h"
11 /**
12  *  ysLayer.h及.m文件内容
13
14  #import <QuartzCore/QuartzCore.h>
15  @interface ysLayer : CALayer
16  @end
17
18  #import "ysLayer.h"
19  @implementation ysLayer
20  -(void)drawInContext:(CGContextRef)ctx
21  {
22     CGContextAddEllipseInRect(ctx, CGRectMake(0, 0, 50, 50));
23     CGContextSetRGBFillColor(ctx, 0, 0, 1, 1.0);
24     CGContextFillPath(ctx);
25  }
26
27  @end
28  */
29
30
31 @interface ViewController ()
32
33 @end
34
35 @implementation ViewController
36
37 - (void)viewDidLoad {
38     [super viewDidLoad];
39     [self diyLayer2];
40     [self diyLayer1];
41 }
42
43 -(BOOL)prefersStatusBarHidden
44 {
45     return YES;
46 }
47
48
49 -(void)diyLayer1
50 {
51     ysLayer *layer = [[ysLayer alloc]init];
52     layer.backgroundColor = [UIColor redColor].CGColor;
53     layer.bounds = CGRectMake(0, 0, 200, 200);
54     layer.anchorPoint = CGPointMake(0, 0);
55     [self.view.layer addSublayer:layer];
56     [layer setNeedsDisplay];
57 }
58
59
60 -(void)diyLayer2
61 {
62     CALayer *layer = [[CALayer alloc]init];
63     layer.backgroundColor = [UIColor blackColor].CGColor;
64     layer.bounds = CGRectMake(0, 0, 200, 200);
65     layer.position = CGPointMake(0, 200);
66     layer.anchorPoint = CGPointZero;
67     layer.delegate = self;//继承自NSObject的类都可以作为Layer的代理
68     [self.view.layer addSublayer:layer];
69     [layer setNeedsDisplay];
70 }
71
72 //代理方法
73 -(void)drawLayer:(CALayer *)layer inContext:(CGContextRef)ctx
74 {
75     CGContextAddEllipseInRect(ctx, CGRectMake(0, 0, 50, 50));
76     CGContextSetRGBFillColor(ctx, 1, 0, 0, 1);
77     CGContextFillPath(ctx);
78 }
79
80 @end