How to Mask Uiviews in iOS

How to mask UIViews in iOS

I've been working on this problem for a couple of hours and have a solution that I think will do what you want. First, create your masking image using whatever means you see fit. Note that we only need the alpha values here, all other colours will be ignored, so make certain that the method you use supports alpha values. In this example I'm loading from a .png file, but don't try it with .jpg files as they don't have alpha values.

Next, create a new layer, assign your mask to its contents and set this new layer to your UIView's own layer, like so: you should find that this masks the UIView and all its attached subviews:

UIImage *_maskingImage = [UIImage imageNamed:@"mask"];
CALayer *_maskingLayer = [CALayer layer];
_maskingLayer.frame = theView.bounds;
[_maskingLayer setContents:(id)[_maskingImage CGImage]];
[theView.layer setMask:_maskingLayer];

With this done, you can set the UIView's background colour to whatever you like and the mask will be used to create a coloured filter.

EDIT: As of iOS8 you can now mask a view simply by assigning another view to its maskView property. The general rules stay the same in that the maskView's alpha layer is used to determine the opacity of the view it is applied to.

Masking a UIView and Auto Layout

As Zev explained, the mask view lives outside of the ordinary view hierarchy and so can't be used together with Auto Layout. I got around this by placing it manually in my view controller's viewDidLayoutSubviews:

-(void)viewDidLayoutSubviews{
    [super viewDidLayoutSubviews];
    CGRect viewToMaskRect = self.viewToMask.bounds;
    CGRect maskRect = CGRectMake(viewToMaskRect.origin.x + 50.0, viewToMaskRect.origin.y + 50.0, 100.0, 100.0);
    [self.theMask setFrame:maskRect];
    [self.viewToMask setMaskView:self.theMask];
}

Simply mask a UIView with a rectangle

Thanks to the link from MSK, this is the way I went with which works well:

// Create a mask layer and the frame to determine what will be visible in the view.
CAShapeLayer *maskLayer = [[CAShapeLayer alloc] init];
CGRect maskRect = CGRectMake(0, 0, 50, 100);

// Create a path with the rectangle in it.
CGPathRef path = CGPathCreateWithRect(maskRect, NULL);

// Set the path to the mask layer.
maskLayer.path = path;

// Release the path since it's not covered by ARC.
CGPathRelease(path);

// Set the mask of the view.
viewToMask.layer.mask = maskLayer;

Masking a UIView

#import <QuartzCore/QuartzCore.h>

needed to be added.

Mask UIView with UIImage by Keeping Transparent Area and Removing Coloured Area

Here is one way...

func getImageWithInvertedPixelsOfImage(image: UIImage) -> UIImage {
    let rect = CGRect(origin: CGPoint(), size: image.size)

    UIGraphicsBeginImageContextWithOptions(image.size, false, 2.0)
    UIGraphicsGetCurrentContext()!.setBlendMode(.copy)
    image.draw(in: rect)
    UIGraphicsGetCurrentContext()!.setBlendMode(.sourceOut)
    UIGraphicsGetCurrentContext()!.setFillColor(UIColor.green.cgColor)
    UIGraphicsGetCurrentContext()!.fill(rect)

    let result = UIGraphicsGetImageFromCurrentImageContext()
    UIGraphicsEndImageContext()
    return result!
}

// I named your original image "WaveMask"
let iWave = UIImage(named: "WaveMask")
let invWave = getImageWithInvertedPixelsOfImage(image: iWave!)

// invWave is now Green where it was alpha, and alpha where it was gray
// and can now be used as a mask

How To Add Border To a UIView With Mask?

Add corner radius to you view on viewDidAppear

@IBOutlet weak var segmentView: UIView!

override func viewDidAppear(_ animated: Bool) {
    super.viewDidAppear(animated)
    segmentView.layer.cornerRadius = segmentView.frame.size.height/2;
    segmentView.layer.borderWidth = 1.0;
    segmentView.clipsToBounds = true

    segmentView.layer.borderColor = UIColor.lightGray.cgColor

    segmentView.layer.shadowColor = UIColor.black.cgColor
    segmentView.layer.shadowOpacity = 0.2
    segmentView.layer.shadowRadius = 10.0
    segmentView.layer.shadowOffset = CGSize(width: 1, height: 1)
    segmentView.layer.masksToBounds = false
}

Sample Output:

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