iOS 图片中间拉伸，两边不拉伸

- (void)viewDidLoad {
    [super viewDidLoad];
    // Do any additional setup after loading the view.
    
    //使图片两边不拉伸，中间拉伸
    UIImage *image = [UIImage imageNamed:@"1.jpg"];
    image = [image stretchableImageWithLeftCapWidth:floorf(image.size.width/2) topCapHeight:floorf(image.size.height/2)];
    
    UIImageView *imageView=[[UIImageView alloc]initWithFrame:CGRectMake(50, 100, 200, 200)];
    imageView.backgroundColor=[UIColor redColor];
    imageView.image=image;
    [self.view addSubview:imageView];
}