通过 CALayer 代理方法绘图

#import "ViewController.h"
#define WIDTH 50
#define PHOTO_HEIGHT 150
@interface ViewController ()

@end

@implementation ViewController

- (void)viewDidLoad
{
    [super viewDidLoad];
    CALayer *layer=[CALayer layer];
    layer.bounds=CGRectMake(, , PHOTO_HEIGHT, PHOTO_HEIGHT);
    layer.position=CGPointMake(, );
    layer.backgroundColor=[UIColor redColor].CGColor;
    layer.cornerRadius=PHOTO_HEIGHT/;
    layer.masksToBounds=YES;

    layer.borderColor=[UIColor whiteColor].CGColor;
    layer.borderWidth=;
    layer.delegate=self;
    [self.view.layer addSublayer:layer];
    [layer setNeedsDisplay];

}
-(void)drawLayer:(CALayer *)layer inContext:(CGContextRef)ctx
{
    CGContextSaveGState(ctx);
    CGContextScaleCTM(ctx, , -);
    CGContextTranslateCTM(ctx, , -PHOTO_HEIGHT);
    UIImage *image=[UIImage imageNamed:@""];
    CGContextDrawImage(ctx, CGRectMake(, , PHOTO_HEIGHT, PHOTO_HEIGHT), image.CGImage);
    CGContextRestoreGState(ctx);
}