将两张图片重叠后显示为新图片

想要实现两张图片重叠后显示为新突破，但是运行后模拟器什么也没显示

代码如下：

- (void)viewDidLoad
{
    [super viewDidLoad];

    image1 = [[UIImage alloc]init];

    image1 = [UIImage imageNamed:@"iphone.png"];

    imageA = [[UIImageView alloc]initWithImage:image1];


    [self merge];

}

-(void)merge
{
  CGSize size = CGSizeMake(320, 480);
    UIGraphicsBeginImageContext(size);

    CGPoint thumbPoint = CGPointMake(0,0);
    imageview.image = imageA.image;
    [imageA.image drawAtPoint:thumbPoint];

    imageB = [[UIImage alloc]init];

    imageB = [UIImage imageNamed:@"Favorites.png"];

    CGPoint starredPoint = CGPointMake(0, 0);
    [imageB drawAtPoint:starredPoint];

    UIImage *imageC = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();
    imageview.image = imageC;

    [self.view addSubview:imageview];

}