Reputation: 469

How do I present a view controller over current context with a custom transition?

I am running into a problem with view controller containment and wanting to present view controllers "over current context" with a custom presentation/animation.

I have a root view controller that has two child view controllers that can be added and removed as children to the root. When these child view controllers present a view controller I want the presentation to be over current context so that when the child that is presenting is removed from the view heirarchy and deallocated the presented modal will be removed as well. Also, if child A presents a view controller, I would expect child B's 'presentedViewController' property to be nil in an "over current context" presentation even if A was still presenting.

Everything works as expected when I set the modalPresentationStyle of my presented view controller to overCurrentContext, and if the child view controllers have definesPresentationContext set to true.

This doesn't work when I would expect it to however if I have modalPresentationStyle set to custom and override shouldPresentInFullscreen returning false in my custom presentation controller.

Here is an example illustrating the problem:

import UIKit

final class ProgressController: UIViewController {
    private lazy var activityIndicatorView = UIActivityIndicatorView(activityIndicatorStyle: .white)
    private lazy var progressTransitioningDelegate = ProgressTransitioningDelegate()

    // MARK: Lifecycle

    override init(nibName nibNameOrNil: String?, bundle nibBundleOrNil: Bundle?) {
        super.init(nibName: nibNameOrNil, bundle: nibBundleOrNil)

        setup()
    }

    required public init?(coder aDecoder: NSCoder) {
        super.init(coder: aDecoder)

        setup()
    }

    override public func viewDidLoad() {
        super.viewDidLoad()

        view.backgroundColor = UIColor(white: 0, alpha: 0)

        view.addSubview(activityIndicatorView)
        activityIndicatorView.startAnimating()
    }

    override func viewDidAppear(_ animated: Bool) {
        super.viewDidAppear(animated)
    }

    override public func viewDidLayoutSubviews() {
        super.viewDidLayoutSubviews()

        activityIndicatorView.center = CGPoint(x: view.bounds.width/2, y: view.bounds.height/2)
    }

    // MARK: Private

    private func setup() {
        modalPresentationStyle = .custom
        modalTransitionStyle = .crossDissolve
        transitioningDelegate = progressTransitioningDelegate
    }
}

final class ProgressTransitioningDelegate: NSObject, UIViewControllerTransitioningDelegate {
    func presentationController(forPresented presented: UIViewController, presenting: UIViewController?, source: UIViewController) -> UIPresentationController? {
        return DimBackgroundPresentationController(presentedViewController: presented, presenting: source)
    }
}

final class DimBackgroundPresentationController: UIPresentationController {
    lazy var overlayView: UIView = {
        let v = UIView()
        v.backgroundColor = UIColor(white: 0, alpha: 0.5)
        return v
    }()

    override var shouldPresentInFullscreen: Bool {
        return false
    }

    override func presentationTransitionWillBegin() {
        super.presentationTransitionWillBegin()

        overlayView.alpha = 0
        containerView!.addSubview(overlayView)
        containerView!.addSubview(presentedView!)

        if let coordinator = presentedViewController.transitionCoordinator {
            coordinator.animate(alongsideTransition: { _ in
                self.overlayView.alpha = 1
            }, completion: nil)
        }
    }

    override func containerViewDidLayoutSubviews() {
        super.containerViewDidLayoutSubviews()

        overlayView.frame = presentingViewController.view.bounds
    }

    override func dismissalTransitionWillBegin() {
        super.dismissalTransitionWillBegin()

        let coordinator = presentedViewController.transitionCoordinator
        coordinator?.animate(alongsideTransition: { _ in
            self.overlayView.alpha = 0
        }, completion: nil)
    }
}

class ViewControllerA: UIViewController {
    override func viewDidAppear(_ animated: Bool) {
        super.viewDidAppear(animated)

        definesPresentationContext = true

        let vc = ProgressController()
        self.present(vc, animated: true) {
        }
    }
}

class ViewController: UIViewController {

    let container = UIScrollView()

    override func viewDidLoad() {
        super.viewDidLoad()

        container.frame = view.bounds
        view.addSubview(container)

        let lhs = ViewControllerA()
        lhs.view.backgroundColor = .red

        let rhs = UIViewController()
        rhs.view.backgroundColor = .blue

        addChildViewController(lhs)
        lhs.view.frame = CGRect(x: 0, y: 0, width: view.bounds.width, height: view.bounds.height)
        container.addSubview(lhs.view)
        lhs.didMove(toParentViewController: self)

        addChildViewController(rhs)
        rhs.view.frame = CGRect(x: view.bounds.width, y: 0, width: view.bounds.width, height: view.bounds.height)
        container.addSubview(rhs.view)
        rhs.didMove(toParentViewController: self)


        container.contentSize = CGSize(width: view.bounds.width * 2, height: view.bounds.height)
    }

    override func viewDidAppear(_ animated: Bool) {
        super.viewDidAppear(animated)
//        let rect = CGRect(x: floor(view.bounds.width/2.0), y: 0, width: view.bounds.width, height: view.bounds.height)
//        container.scrollRectToVisible(rect, animated: true)
    }
}

This will show a ViewController with a scroll view that contains two child view controllers
The red view controller on the left hand side will present a progress view controller that should present over current context.
If the view controller was presented properly "over current context" then you would be able to scroll the scrollview, and if you checked the "presentedViewController" property of the blue right hand side view controller then it should be nil. Neither of these are true.

If you change the setup() function on ProgressController to:

private func setup() {
    modalPresentationStyle = .overCurrentContext
    modalTransitionStyle = .crossDissolve
    transitioningDelegate = progressTransitioningDelegate
}

the presentation/view heirarchy will behave as expected, but the custom presentation will not be used.

Apple's docs for shouldPresentInFullscreen seem to indicate that this should work:

The default implementation of this method returns true, indicating that the presentation covers the entire screen. You can override this method and return false to force the presentation to display only in the current context.

If you override this method, do not call super.

I tested this in Xcode 8 on iOS 10 and Xcode 9 on iOS 11 and the above code would not work as expected in either case.

Upvotes: 18

How do I present a view controller over current context with a custom transition?

Answers (3)

Related Questions