image的原生

- (void)viewDidLoad
{
    [super viewDidLoad];
    // Do any additional setup after loading the view.
    
    UIImageView *imageView=[[UIImageView alloc]initWithFrame:CGRectMake(50, 100, 44, 44)];
    imageView.image=[self defaultImage];
    [self.view addSubview:imageView];
    
}
-(UIImage *)defaultImage {
    static UIImage *defaultImage = nil;
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        UIGraphicsBeginImageContextWithOptions(CGSizeMake(20.f, 13.f), NO, 0.0f);
        
        [[UIColor blackColor] setFill];
        [[UIBezierPath bezierPathWithRect:CGRectMake(0, 0, 20, 1)] fill];
        [[UIBezierPath bezierPathWithRect:CGRectMake(0, 5, 20, 1)] fill];
        [[UIBezierPath bezierPathWithRect:CGRectMake(0, 10, 20, 1)] fill];
        
        [[UIColor whiteColor] setFill];
        [[UIBezierPath bezierPathWithRect:CGRectMake(0, 1, 20, 2)] fill];
        [[UIBezierPath bezierPathWithRect:CGRectMake(0, 6,  20, 2)] fill];
        [[UIBezierPath bezierPathWithRect:CGRectMake(0, 11, 20, 2)] fill];
        
        defaultImage = UIGraphicsGetImageFromCurrentImageContext();
        UIGraphicsEndImageContext();
        
    });
    return defaultImage;
}