Transparent Circle at Middle of UIImageView IOS

问题

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];

回答1:

One way to do it is like this. I have an image view with my main image, and another image called BlackCircle which is just a 40x40 black circle (that I made in the Pixen app). The action method causes the main image to become transparent where it is overlapped by the black circle, which I've placed in the center of the main image:

@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;
}

回答2:

Instead of trying to make a portion of Imageview transparent, try to make in image transparent at areas you want it to by setting corresponding alphas to 0.

来源：https://stackoverflow.com/questions/20064115/transparent-circle-at-middle-of-uiimageview-ios