绘制垃圾图像

#import "MyLayer.h"

@implementation MyLayer


- (void)drawInContext:(CGContextRef)ctx
{
    // 设置填充色
    CGContextSetRGBFillColor(ctx, 1, 0, 0, 1);
    // 椭圆
    CGContextAddEllipseInRect(ctx, CGRectMake(0, 0, 50, 50));
    // 填充路径
    CGContextFillPath(ctx);
}
@end

#import "MyView.h"

@implementation MyView


// Only override drawRect: if you perform custom drawing.
// An empty implementation adversely affects performance during animation.
- (void)drawRect:(CGRect)rect {
    // Drawing code
    
    
    CGContextRef ctx =  UIGraphicsGetCurrentContext();
    // 设置rgb填充颜色
    CGContextSetRGBFillColor(ctx, 1, 0, 0, 1);
    // 矩形内部添加椭圆
    CGContextAddEllipseInRect(ctx, CGRectMake(0, 0, 50, 50));
    // 填充路径
    CGContextFillPath(ctx);
}

#import "ViewController.h"
#import "MyView.h"
#import "MyLayer.h"

@interface ViewController ()


@end

@implementation ViewController

- (void)viewDidLoad {
    [super viewDidLoad];
    // Do any additional setup after loading the view, typically from a nib.
    
    CALayer *layer = [CALayer layer];
    //大小
    layer.bounds = CGRectMake(0, 0, 100, 100);
    //颜色
    layer.backgroundColor = [UIColor blackColor].CGColor;
    //锚点
    layer.anchorPoint = CGPointZero;
    //位置
    layer.position = CGPointMake(100, 100);
    //代理
    layer.delegate = self;
    [layer setNeedsDisplay];
    [self.view.layer addSublayer:layer];
    
    
    [self diyLayer];
      
    
}
#pragma mark - 图层的代理方法
//绘制代理
- (void)drawLayer:(CALayer *)layer inContext:(CGContextRef)ctx
{
    CGContextSetRGBFillColor(ctx, 1, 0, 0, 1);
    CGContextAddRect(ctx, CGRectMake(0, 0, 20, 20));
    CGContextFillPath(ctx);
}

- (void)diyLayer
{
    MyLayer *layer = [MyLayer layer];
    layer.bounds = CGRectMake(0, 0, 100, 100);
    layer.backgroundColor = [UIColor blueColor].CGColor;
    layer.anchorPoint = CGPointZero;
    [layer setNeedsDisplay];
    [self.view.layer addSublayer:layer];
}

@end