Extension for convenient UIViewController parenting

UIViewController+Parenting.swift

//
//  UIViewController+Parenting.swift
//
//  Created by Kaden, Joshua on 5/23/19.
//

import UIKit

extension UIViewController {
    
    /// Removes all child view controllers by calling the appropriate methods.
    ///
    /// The children's `willMove(toParent: nil)` methods are called.
    /// Their views are also removed from the view hierarchy. Finally, their
    /// `removeFromParent` methods are called.
    func abandonChildrenViewControllers() {
        children.forEach { $0.leaveParentViewController() }
    }
    
    /// Tells the view controller to add the supplied view controller as a child, by calling the appropriate methods.
    ///
    /// This convenience method calls `addChild`, adds the child
    /// view controller's view to the view hierarchy, and calls the child's
    /// `didMove(toParent)` method.
    ///
    /// The child view controller's view is added to the view hierarchy,
    /// either to the main view, or the `targetView` (if supplied).
    ///
    /// - Parameters:
    ///   - childController: The view controller to be added as a child.
    ///   - targetView: (optional) The child view controller's view will be added to this view.
    func adoptChildViewController(_ childController: UIViewController, targetView: UIView? = nil) {
        addChild(childController)
        if let targetView = targetView {
            targetView.addSubview(childController.view)
        } else {
            view.addSubview(childController.view)
        }
        childController.didMove(toParent: self)
    }
    
    /// Tells a child view controller to remove itself from its parent, by calling the appropriate methods.
    ///
    /// The child's `willMove(toParent: nil)` method is called.
    /// Its view is also removed from the view hierarchy. Finally, its
    /// `removeFromParent` method is called.
    func leaveParentViewController() {
        willMove(toParent: nil)
        view.removeFromSuperview()
        removeFromParent()
    }
}