A utility iOS protocol that allows for easy instantiation of classes that are associated with a Nib.

NibLoadable.swift

/// A type that can be loaded from an associated nib.
protocol NibLoadable: class {

    /// The name of the nib for the loadable class.
    static var nibName: String { get }
    /// The bundle the nib is contained within for the loadable class.
    static var nibBundle: Bundle { get }

}

extension NibLoadable {

    static var nibName: String {
        // defaults to the name of the class
        return String(describing: Self.self)
    }

    static var nibBundle: Bundle {
        // defaults to the name of the class
        return Bundle(for: Self.self)
    }

    /// An instance of the nib for the loadable class.
    static var nib: UINib {
        return UINib(nibName: Self.nibName, bundle: self.nibBundle)
    }

}

extension NibLoadable where Self: UIView {

    /// Instantiates and returns the root view of the nib.
    private func instantiate<T: UIView>() -> T {
        guard let instance = Self.nib.instantiate(withOwner: self, options: nil).first as? T else {
            fatalError("Failed to instantiate nib named '\(Self.nibName)'")
        }

        return instance
    }

    /// Instantiates the view from the nib, and adds it as a subview to the current instance
    /// constrained to all sides.
    func loadFromNib() {
        let view = instantiate()
        addSubview(view)
        view.translatesAutoresizingMaskIntoConstraints = false

        NSLayoutConstraint.activate([
            view.topAnchor.constraint(equalTo: self.topAnchor, constant: 0.0),
            view.bottomAnchor.constraint(equalTo: self.bottomAnchor, constant: 0.0),
            view.leftAnchor.constraint(equalTo: self.leftAnchor, constant: 0.0),
            view.rightAnchor.constraint(equalTo: self.rightAnchor, constant: 0.0)
        ])
    }

}