UIImageView IOS中间的透明圆圈

I need to make UIImageView transparent at the Middle Position(Round Circle ..See attached image)
I should be able to see the Behind Subviews of UIImageView via that middle circle...i tried CAShapeLayer..but i am not able to see the behind subviews of UIImageView..Please help me..Sorry for my English....

    CAShapeLayer *circleLayer = [CAShapeLayer layer];

    // Give the layer the same bounds as your image view
    [circleLayer setBounds:CGRectMake(100.0f, 100.0f, [((UIImageView *)view) bounds].size.width,
                                      [((UIImageView *)view) bounds].size.height)];
    // Position the circle anywhere you like, but this will center it
    // In the parent layer, which will be your image view's root layer
    [circleLayer setPosition:CGPointMake(100,
                                         100)];
    // Create a circle path.
    UIBezierPath *path = [UIBezierPath bezierPathWithOvalInRect:
                          CGRectMake(100.0f, 100.0f, 50.0f, 50.0f)];
    // Set the path on the layer
    [circleLayer setPath:[path CGPath]];
    // Set the stroke color
    [circleLayer setStrokeColor:[[UIColor redColor] CGColor]];
    // Set the stroke line width
    [circleLayer setLineWidth:2.0f];

    // Add the sublayer to the image view's layer tree
    [circleLayer setOpacity:0.5];
[[((UIImageView *)view) layer] addSublayer:circleLayer];

一种方法是这样的。我有一个包含主图像的图像视图，以及另一个名为 BlackCircle 的图像，它只是一个 40x40 的黑色圆圈（我在 Pixen 应用程序中制作的）。该操作方法使主图像在与黑色圆圈重叠的地方变得透明，我将其放置在主图像的中心：

@interface ViewController ()
@property (weak,nonatomic) IBOutlet UIImageView *imageView;
@end

@implementation ViewController

-(void)viewDidLoad {
    [super viewDidLoad];
    self.imageView.image = [UIImage imageNamed:@"House.tiff"];
    self.imageView.backgroundColor = [UIColor clearColor];
}


-(IBAction)createAlphaClippedImage:(id)sender {
    UIImage *circleImage = [UIImage imageNamed:@"BlackCircle.png"];
    UIImage *mainImage = [UIImage imageNamed:@"House.tiff"];

    UIGraphicsBeginImageContextWithOptions(mainImage.size, NO, 0.0);

    CGRect imageRect = CGRectMake(0.0f, 0.0f, mainImage.size.width, mainImage.size.height);
    CGRect centerCircleRect = CGRectMake(mainImage.size.width/2.0 - circleImage.size.width/2.0, mainImage.size.height/2.0 - circleImage.size.height/2.0,circleImage.size.width,circleImage.size.height);

    [mainImage drawInRect:imageRect];
    [circleImage drawInRect:centerCircleRect blendMode:kCGBlendModeXOR alpha:1.0];

    UIImage *image = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();

    self.imageView.image = image;
}