What do I need for masking a UIImageView and how do I do it in Swift 3?

Question

I was wondering what I would need if I wanted to use a mask image to get my `UIImageView` in a specific shape. From what I understand, to create a mask, I need to have an image with the shape of the mask all black on top of a white background. Something like this, for example: First of all, is this sufficient to shape an image view, and if so, how do I do it in Swift 3? I can only find masking code that is either outdated or written in Objective-C. I've tried simply assigning the image above to an `UIImageView` and then assign the image view to the `mask` property of the `UIImageView` I want to shape, like so: ``` self.defaultImageView.mask = self.maskImageView ``` This didn't do anything. It just made `self.maskImageView` disappear (both image view's added through the storyboard and connected using `IBOutlet` properties). I'm sure I'm forgetting to do something. It can't be this simple. I would appreciate it if someone could help me out. Like I said, I put both image views on the exa…

Accepted Answer

You should use a png image, which supports transparency, unlike jpg.

In Photoshop your image should look similar to this:

It doesn't matter if your shape is black or white. What matters is transparency of each pixel. Opaque area (black in this case) will be visible and transparent area will get trimmed.

Edit:

You should not create mask view from storyboard if you do so. It is not going to be a part of your view hierarchy. Just add it programmatically like this:

```
let maskView = UIImageView()

override func viewDidLoad() {
    super.viewDidLoad()
    maskView.image = UIImage(named: "mask")
    imageView.mask = maskView        
}

override func viewDidLayoutSubviews() {
    super.viewDidLayoutSubviews()
    maskView.frame = imageView.bounds
}
```

Output:

Here is a test project to show how it's working.

What do I need for masking a UIImageView and how do I do it in Swift 3?

Solution

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