Adding and Removing Child View Controllers

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Adding and removing child view controllers ensures that the parent view controller knows of its children. This will help when doing things like calling a modal from a child view that has been added to the parent. This behavior can be buggy if the parent doesn't know that it's connected to the child. Another reason is so that viewWillAppear, viewDidAppear, viewWillDisappear, and viewDidDisappear work consistently.

Adding a child view controller

addChildViewController(yourViewController)
view.addSubview(yourViewController.view)
yourViewController.didMove(toParentViewController: self)

Example function

func displayContentController(content: UIViewController) {
    addChildViewController(content)
    self.view.addSubview(content.view)
    content.didMove(toParentViewController: self)
}

Removing a child view controller

yourViewController.willMove(toParentViewController: nil)
yourViewController.view.removeFromSuperview()
yourViewController.removeFromParentViewController()

Example function

func hideContentController(content: UIViewController) {
    content.willMove(toParentViewController: nil)
    content.view.removeFromSuperview()
    content.removeFromParentViewController()
}