viewWithTag:

There’s been lots of debate on whether you should use a UIView’s tag or not. The truth is you don’t always have the chance to decice and you’ve got to use it.

One good example of not being able to make a choice would be when using an extension, specially a protocol extension. Extensions can’t hold stored properties, so you can’t really have a reference to the view like this:

protocol LoadingViewController {
    
    var isLoading: Bool { get set }
}

extension LoadingViewController where Self: UIViewController {
    
    let activityIndicatorView: UIActivityIndicatorView
}

In such cases you may want to build and refer to your view hierarchy by using tags.

It’s unfortunate that in UIView’s tag property is an Int, because numbers are so easy to be repeated and so unexpresive. Say you tag a view 10, does that say anything about the view? What if someone else already used 10 for another subview of that view?

Wouldn’t it be better to be able to tag that with a String?

That’s when this extension may come in handy:

extension UIView {
    
    func view(with key: String) -> UIView? {
        
        return self.viewWithTag(key.hashValue)
    }
    
    func setKey(_ key: String?) {
        
        self.tag = key?.hashValue ?? 0 // Default for view.tag.
    }
}

It introduces the concept of key which is a String and it’s actually just a wrapper for the tag, so you get the exact same behavoir.

Now you can go from something like this:

let childViewKey = 12345

let parentView = UIView()
let childView = UIView()

childView.tag = childViewKey
parentView.addSubview(childView)

let viewWithKey = parentView.viewWithTag(childViewKey)

to something like:

let childViewKey = "com.myApp.notificationsPane.optionSwitch"

let parentView = UIView()
let childView = UIView()

childView.setKey(childViewKey)
parentView.addSubview(childView)

let viewWithKey = parentView.view(with: childViewKey)