A presentation controller to use for presenting a view controller modally, which can be dismissed by a pull down gesture. The presented view controller's height is also adjustable.

SheetModalPresentationController.swift

import UIKit

extension UIView {
    
    var allSubviews: [UIView] {
        subviews + subviews.flatMap { $0.allSubviews }
    }
    
    func firstSubview<T: UIView>(of type: T.Type) -> T? {
        allSubviews.first { $0 is T } as? T
    }
    
    func findFirstResponder() -> UIView? {
        for subview in subviews {
            if subview.isFirstResponder {
                return subview
            }
            
            if let recursiveSubView = subview.findFirstResponder() {
                return recursiveSubView
            }
        }

        return nil
    }
    
}

extension UIApplication {
    
    static var statusBarHeight: CGFloat {
        Self.shared.statusBarFrame.height
    }
    
}

extension UIViewController {
        
    /// Return the preferred height of the view controller, taking scrollviews into account.
    var preferredHeight: CGFloat {
        /// If the view controller provides it's own preferred size, use it.
        if preferredContentSize.height > 0 {
            return preferredContentSize.height
        }
        
        return calculatePreferredHeight()
    }
    
    func calculatePreferredHeight() -> CGFloat {
        // Insets are all zero intially, but once setup they will influence the results of the systemLayoutSizeFitting method.
        let insets = view.safeAreaInsets.top + view.safeAreaInsets.bottom
        // We substract the insets from the height to always get the actual height of only the view itself.
        var height = max(0, view.systemLayoutSizeFitting(UIView.layoutFittingCompressedSize).height - insets)
                
        // Support for UITableViewControllers.
        if let tableView = view as? UITableView {
            height += tableView.contentSize.height + tableView.contentInset.top + tableView.contentInset.bottom
            return height
        }
        
        // Include scroll views in the height calculation.
        height += view.subviews.filter { $0 is UIScrollView }.reduce(CGFloat(0), { result, view in
            if view.intrinsicContentSize.height <= 0 {
                // If a scroll view does not have an intrinsic content size set, use the content size.
                let scrollView = view as! UIScrollView
                return result + scrollView.contentSize.height + scrollView.contentInset.top + scrollView.contentInset.bottom
            } else {
                return result
            }
        })
                
        return height
    }
    
    func requestHeightUpdate() {
        // Set the preferredContentSize to force a preferredContentSizeDidChange call in the parent.
        preferredContentSize.height += 1
        preferredContentSize.height = 0
    }
    
        
    func presentAsSheet(_ vc: UIViewController, isDismissable: Bool) {
        let presentationController = SheetModalPresentationController(presentedViewController: vc,
                                                                      presenting: self,
                                                                      isDismissable: isDismissable)
        vc.transitioningDelegate = presentationController
        vc.modalPresentationStyle = .custom
        present(vc, animated: true)
    }

}

final class SheetModalPresentationController: UIPresentationController {
    
    // MARK: Private Properties
        
    private let isDismissable: Bool
    private let interactor = UIPercentDrivenInteractiveTransition()
    private let dimmingView = UIView()
    private var propertyAnimator: UIViewPropertyAnimator!
    private var isInteractive = false
    private var navigationController: UINavigationController {
        presentedViewController as! UINavigationController
    }
    private var nestedViewController: UIViewController? {
        navigationController.viewControllers.last
    }
    private var scrollView: UIScrollView? {
        nestedViewController?.view as? UIScrollView ?? nestedViewController?.view.firstSubview(of: UIScrollView.self)
    }
    private let topOffset = UIApplication.statusBarHeight + 20

    // MARK: Public Properties
    
    override var frameOfPresentedViewInContainerView: CGRect {
        guard let containerBounds = containerView?.bounds,
            let nestedViewController = nestedViewController,
            let window = UIApplication.shared.keyWindow else { return .zero }
        
        let extraPadding = navigationController.navigationBar.frame.height +
                            navigationController.additionalSafeAreaInsets.top +
                            window.safeAreaInsets.bottom +
                            nestedViewController.additionalSafeAreaInsets.top +
                            nestedViewController.additionalSafeAreaInsets.bottom
        var frame = containerBounds
        frame.size.height = min(nestedViewController.preferredHeight + extraPadding,
                                containerBounds.height - topOffset)
        frame.origin.y = containerBounds.height - frame.size.height
        return frame
    }
        
    // MARK: Initializers
    
    init(presentedViewController: UIViewController, presenting presentingViewController: UIViewController?,
         isDismissable: Bool) {
        self.isDismissable = isDismissable
        
        super.init(presentedViewController: presentedViewController, presenting: presentingViewController)
        
        registerForKeyboardNotifications()
    }
    
    // MARK: Public Methods

    override func presentationTransitionWillBegin() {
        guard let containerBounds = containerView?.bounds, let presentedView = presentedView else { return }
                            
        // Configure the presented view.
        containerView?.addSubview(presentedView)
        presentedView.layoutIfNeeded()
        presentedView.frame = frameOfPresentedViewInContainerView
        presentedView.frame.origin.y = containerBounds.height
        presentedView.layer.masksToBounds = true
        presentedView.layer.maskedCorners = [.layerMinXMinYCorner, .layerMaxXMinYCorner]
        presentedView.layer.cornerRadius = 40
        
        // Add a dimming view below the presented view controller.
        dimmingView.backgroundColor = .black
        dimmingView.frame = containerBounds
        dimmingView.alpha = 0
        containerView?.insertSubview(dimmingView, at: 0)
        
        // Add pan gesture recognizers for interactive dismissal.
        presentedView.addGestureRecognizer(UIPanGestureRecognizer(target: self, action: #selector(handlePan(_:))))
        scrollView?.panGestureRecognizer.addTarget(self, action: #selector(handlePan(_:)))
        
        // Add tap recognizer for sheet and keyboard dismissal.
        dimmingView.addGestureRecognizer(UITapGestureRecognizer(target: self, action: #selector(handleDismiss)))
        
        presentedViewController.transitionCoordinator?.animate(alongsideTransition: { [unowned self] _ in
            self.dimmingView.alpha = 0.5
        })
    }
    
    override func dismissalTransitionWillBegin() {
        presentedViewController.transitionCoordinator?.animate(alongsideTransition: { [unowned self] _ in
            self.dimmingView.alpha = 0
        })
    }
    
    override func dismissalTransitionDidEnd(_ completed: Bool) {
        // Not setting this to nil causes a retain cycle for some reason.
        propertyAnimator = nil
    }
    
    override func preferredContentSizeDidChange(forChildContentContainer container: UIContentContainer) {
        super.preferredContentSizeDidChange(forChildContentContainer: container)
                
        if propertyAnimator != nil && !propertyAnimator.isRunning {
            presentedView?.frame = frameOfPresentedViewInContainerView
            presentedView?.layoutIfNeeded()
        }
    }

    // MARK: Private Methods
        
    @objc
    private func handleDismiss() {
        presentedView?.endEditing(true)
        if isDismissable {
            presentedViewController.dismiss(animated: true)
        }
    }

    @objc
    private func handlePan(_ gesture: UIPanGestureRecognizer) {
        guard isDismissable, let containerView = containerView else { return }
        
        limitScrollView(gesture)
        
        let percent = gesture.translation(in: containerView).y / containerView.bounds.height
        switch gesture.state {
        case .began:
            if !presentedViewController.isBeingDismissed && scrollView?.contentOffset.y ?? 0 <= 0 {
                isInteractive = true
                presentedViewController.dismiss(animated: true)
            }
        case .changed:
            interactor.update(percent)
        case .cancelled:
            interactor.cancel()
            isInteractive = false
        case .ended:
            let velocity = gesture.velocity(in: containerView).y
            interactor.completionSpeed = 0.9
            if percent > 0.3 || velocity > 1600 {
                interactor.finish()
            } else {
                interactor.cancel()
            }
            isInteractive = false
        default:
            break
        }
    }

    private func limitScrollView(_ gesture: UIPanGestureRecognizer) {
        guard let scrollView = scrollView else { return }
        if interactor.percentComplete > 0 {
            // Don't let the scroll view scroll while dismissing.
            scrollView.contentOffset.y = -scrollView.adjustedContentInset.top
        }
    }
    
    /// Handle the keyboard.
    
    private func registerForKeyboardNotifications() {
        NotificationCenter.default.addObserver(self, selector: #selector(keyboardToggled(notification:)),
                                               name: UIResponder.keyboardWillShowNotification, object: nil)
        NotificationCenter.default.addObserver(self, selector: #selector(keyboardToggled(notification:)),
                                               name: UIResponder.keyboardWillHideNotification, object: nil)
    }
    
    @objc
    private func keyboardToggled(notification: NSNotification) {
        guard let containerHeight = containerView?.bounds.height,
            let presentedView = presentedView,
            let textInput = presentedView.findFirstResponder(),
            let textInputFrame = textInput.superview?.convert(textInput.frame, to: presentedView.superview)
        else {
            return assertionFailure()
        }
        
        // Adjust the presented view to move the active text input out of the keyboards's way (if needed).
        if notification.name == UIResponder.keyboardWillShowNotification {
            guard let keyboardFrame = (notification.userInfo?[UIResponder.keyboardFrameEndUserInfoKey] as? NSValue)?.cgRectValue
            else { return assertionFailure() }
            
            let keyboardOverlap = textInputFrame.maxY - keyboardFrame.minY + 20
            if keyboardOverlap > 0 {
                presentedView.frame.origin.y = max(presentedView.frame.minY - keyboardOverlap, topOffset)
            }
        } else if notification.name == UIResponder.keyboardWillHideNotification {
            presentedView.frame.origin.y = containerHeight - presentedView.frame.size.height
        }
    }

}

// MARK: UIViewControllerAnimatedTransitioning

extension SheetModalPresentationController: UIViewControllerAnimatedTransitioning {

    func transitionDuration(using transitionContext: UIViewControllerContextTransitioning?) -> TimeInterval {
        0.5
    }

    func animateTransition(using transitionContext: UIViewControllerContextTransitioning) {
        interruptibleAnimator(using: transitionContext).startAnimation()
    }

    func interruptibleAnimator(using transitionContext: UIViewControllerContextTransitioning) -> UIViewImplicitlyAnimating {
        propertyAnimator = UIViewPropertyAnimator(duration: transitionDuration(using: transitionContext),
                                                  timingParameters: UISpringTimingParameters(dampingRatio: 1.0,
                                                                                            initialVelocity: CGVector(dx: 1, dy: 1)))
        propertyAnimator.addAnimations { [unowned self] in
            if self.presentedViewController.isBeingPresented {
                transitionContext.view(forKey: .to)?.frame = self.frameOfPresentedViewInContainerView
            } else {
                transitionContext.view(forKey: .from)?.frame.origin.y = transitionContext.containerView.frame.maxY
            }
        }
        propertyAnimator.addCompletion { _ in
            transitionContext.completeTransition(!transitionContext.transitionWasCancelled)
        }
        return propertyAnimator
    }

}

// MARK: UIViewControllerTransitioningDelegate

extension SheetModalPresentationController: UIViewControllerTransitioningDelegate {
    
    func presentationController(forPresented presented: UIViewController, presenting: UIViewController?,
                                source: UIViewController) -> UIPresentationController? {
        self
    }
    
    func animationController(forPresented presented: UIViewController, presenting: UIViewController,
                             source: UIViewController) -> UIViewControllerAnimatedTransitioning? {
        self
    }
    
    func animationController(forDismissed dismissed: UIViewController) -> UIViewControllerAnimatedTransitioning? {
        self
    }
    
    func interactionControllerForDismissal(using animator: UIViewControllerAnimatedTransitioning) -> UIViewControllerInteractiveTransitioning? {
        isInteractive ? interactor : nil
    }

}

@vinczebalazs: thank you, it works fine but the presented (View-Controller) which I'm dismissing has a video when I dismiss it, the video still running in the background, even if I pause the video it doesn't dismiss from the memory,
please any help?

@ioslam That happens because your property animator has strong reference to UIViewControllerContextTransitioning, which has strong reference to UIPresentationController. So you have a reference cycle. To break cycle you can set weak reference to UIViewControllerContextTransitioning in your animator.

propertyAnimator.addAnimations { [weak transitionContext] in
            // Move the view down.
           guard let transitionContext = transitionContext else { return }
            transitionContext.view(forKey: .from)?.frame.origin.y = transitionContext.containerView.frame.maxY
        }
        propertyAnimator.addCompletion { [weak transitionContext] _ in
           guard let transitionContext = transitionContext else { return }
            transitionContext.completeTransition(!transitionContext.transitionWasCancelled)
        }

@Pyxisq , yeah now the problem is fixed, your explanation is quite right, thank you so much for your reply.

@vinczebalazs: thanks for sharing this useful snippet. It is really close what I want and I managed to do something UIView.animate, however as you mentioned about it in your related blog post it does not work very well when it comes to animation and dragging. So I wanted to make upper radial corners to be shown and I managed to do it by playing with frame inside frameOfPresentedViewInContainerView. Just one more thing though, I want it to follow gesture upwards. Like downward gesture but opposite direction and with upper limit. I tried to disable gesture.translation(in: gestureView).y >= 0 from the code and it did not work. Afterwards, I looked for the UIPercentDrivenInteractiveTransition's docs and it says update will work when the percent is in between 0 and 1. I have no idea what else to do. This kind of animating, I am not familiar with.

@vinczebalazs: thank you, it works fine but the presented (View-Controller) which I'm dismissing has a video when I dismiss it, the video still running in the background, even if I pause the video it doesn't dismiss from the memory,
please any help?

Updated the Gist to address this issue.

@vinczebalazs: thanks for sharing this useful snippet. It is really close what I want and I managed to do something UIView.animate, however as you mentioned about it in your related blog post it does not work very well when it comes to animation and dragging. So I wanted to make upper radial corners to be shown and I managed to do it by playing with frame inside frameOfPresentedViewInContainerView. Just one more thing though, I want it to follow gesture upwards. Like downward gesture but opposite direction and with upper limit. I tried to disable gesture.translation(in: gestureView).y >= 0 from the code and it did not work. Afterwards, I looked for the UIPercentDrivenInteractiveTransition's docs and it says update will work when the percent is in between 0 and 1. I have no idea what else to do. This kind of animating, I am not familiar with.

If you send me some code I can take a look

There is also an updated version of this snippet with automatic height calculation and some other improvements!

@vinczebalazs here is my code.

    @objc private func handleDismiss(_ sender: UIPanGestureRecognizer) {
        let dragOnY = sender.translation(in: self.view).y
        let stableYPosition =  -self.sheetHeight + 10

        switch sender.state {
        case .changed:
            if dragOnY + stableYPosition > stableYPosition - 50 {
                UIView.animate(withDuration: 0.3, delay: 0, usingSpringWithDamping: 0.7, initialSpringVelocity: 1, options: .curveEaseOut, animations:{
                    self.view.transform = dragOnY < 100 ? CGAffineTransform(translationX: 0, y:  stableYPosition + dragOnY) : .identity
                })
            }
            if self.view.transform.ty > 0 {
                dismiss(animated: true, completion: nil)
            }
        case .ended:
            if dragOnY < 100 {
                UIView.animate(withDuration: 0.3, delay: 0, usingSpringWithDamping: 0.7, initialSpringVelocity: 1, options: .curveEaseOut, animations:{
                    self.view.transform = CGAffineTransform(translationX: 0, y: stableYPosition)
                })
            } else {
                self.dismiss(animated: true, completion: nil)
            }
        default:break
        }
    }

I can share the full snippet if you want.

If I understand correctly, you want to allow the user to drag upwards a little even if when the view is not being dismissed. First off, you should not animate the view along a gesture, instead do something like this:

presentedView?.frame.origin.y = startY + gesture.translation(in: containerView).y * 0.3

Make sure you set startY to the current y position of the view's frame when the gesture begins. We use a multiplier on the translation to move the view slower than the user's finer. This signals to the user that the gesture is "not allowed". Once the gesture ended, you can perform a spring animation (I recommend a damping of 1.0) to have it bounce back to the startY.

Hope this helps.

yeah that is my intention. I will try your answer and let you know about the result. However I quite did not get where can I change damping while not using UIView.animate

yeah that is my intention. I will try your answer and let you know about the result. However I quite did not get where can I change damping while not using UIView.animate

I have tried the line with various configurations and places. could not make it work, the presentedView just goes berzerk when I add the line somewhere.

Sorry for the late reply! I am very busy at the moment and don't really have time to debug the issue. However, it's been a while since I posted this gist and have been using an updated version of the code (which I did not experience any issues with). I updated the gist with the new code. It's a bit more complex, but has support for scroll views and moving the view up when the keyboard is toggled. Let me know if it works for you!

Everything works as expected but there's one problem that i'm facing, If anyone could help me with that.
I'm able to present view controller as bottom sheet but my view controller also has a texfield and i'm moving my viewcontroller up when keyboard shows and move it down when keyboard closes.

But my view controller doesn't come down when i'm hiding keyboard