What does the File’s Owner do?

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Main Source: 🔗 Ace the iOS Interview

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TL/DR

When you load a .xib file and specify the owner property,the class responsible for loading the .xib now becomes the File's Owner.

open func loadNibNamed(_ name: String, owner: Any?,
options: [UINib.OptionsKey : Any]? = nil) -> [Any]?

// In ViewController.swift
Bundle.main.loadNibNamed("ExampleView", owner: self, options: nil)

Put simply, the File’s Owner is responsible for loading the .xib and facilitating communication between the code and the elements defined in the view. In the example above, ViewController initiates loading the .xib file therebymaking it the File’s Owner. As a result, it will now serve as the middle-man between the .xib file and our application’s code.

Once the .xib file has completed loading, the File’sOwner is responsible for managing the view's contents and binding all of the declared IBOutlets and IBActions in your code to the view's corresponding UI components.

When we specify the File’s Owner in our .xib directly, we're effectively assigning a placeholder value that says -"This class will load me, interact with my UI, and create the necessary bindings to my various UI elements".

It's important to recognize that the File’s Owner is an independent entity and not a part of, nor bound to, the .xib itself - it’s just the class that assumes this middle-man responsibility.