DetentSheetPresentationController

A backport for UIKit's UISheetPresentationController back to iOS 13+ as well as a wrapper for SwiftUI via a ViewModifier.

Like Apple's implemention it has a .large() that is like a regular sheet and a .medium() detent that takes up half of the display, but unlike Apple's, this package has a third detent: .small(), that takes up a quater of the display, similar to the sheet in Apple's Maps app.

How to use in UIKit

For presenting from a UIViewController you'll need to instantiate a custom TransitioningDelegate in the form of DetentTransitionDelegate (1)

NOTE: You will need to call it something other than "transitioningDelegate" to avoid overriding the one that comes from UIViewController

Then you can set your custom configs on the transitionDelegate (2) before setting it to the modal's transitioningDelegate (3) and calling present.

final class ViewController: UIViewController {
    // 1
    lazy var transitionDelegate = DetentTransitionDelegate()

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

    @IBAction func showSheet(_ sender: UIButton) {
        let storyboard = UIStoryboard(name: "Main", bundle: nil)
        let sheetVC = storyboard.instantiateViewController(identifier: "ShownVC")
        // 2
        transitionDelegate.detents = [.small(), .medium(), .large()]
        // 3
        sheetVC.transitioningDelegate = transitionDelegate
        sheetVC.modalPresentationStyle = .custom

        present(sheetVC, animated: true)
    }

}

For the UIViewController that is being presented you'll need to do some set up if you want it to have knowlege of the currentDetent:

1. Cast its presentationController to DetentSheetPresentationController.
2. Set the presentationController.detentDelegate to self and confrom the UIViewController to DetentSheetPresentationControllerDelegate.
3. The detentDelegate has a method called detentSheetPresentationControllerDidChangeSelectedDetentIdentifier that is called everytime the selectedDetentIdentifier is changed.

final class ShownViewController: UIViewController, DetentSheetPresentationControllerDelegate {

    override func viewDidLoad() {
        super.viewDidLoad()
        // 1
        let presentationController = presentationController as? DetentSheetPresentationController
        // 2
        presentationController?.detentDelegate = self
    }
    // 3
    func detentSheetPresentationControllerDidChangeSelectedDetentIdentifier(_ detentSheetPresentationController: DetentSheetPresentationController) {
        guard let currentDetent = detentSheetPresentationController.selectedDetentIdentifier else { return }
    }
}

https://user-images.githubusercontent.com/59975039/172373027-0992e088-fe64-4823-8f2e-e29417023d00.mp4

How to use in SwiftUI

In SwiftUI there is a ViewModifier called .detentSheet that you can power via a State change using the selectedDetentIdentifier:

1. Create a State for DetentSheetPresentationController.Detent.Identifier? so that when you give it a value it presents the detentSheet to that size.
2. You can set all your configs in the arguments for the .detentSheet such as allowedDentents.
3. You can then pass in the selectedDetentId via a Binding so that the presented view has knowlege of it's current detent and can set it to nil when it wants to be dismissed.

struct ContentView: View {
    // 1
    @State private var selectedDetentIdentifier: DetentSheetPresentationController.Detent.Identifier?

    var body: some View {
        Button("Show SwiftUI Sheet") {
            selectedDetentIdentifier = .small
        }
        // 2
        .detentSheet(
            selectedDetentIdentifier: $selectedDetentIdentifier,
            allowedDetents: [.small(), .medium(), .large()]
        ) {
            // 3
            PresentedView(selectedDetentId: $selectedDetentIdentifier)
        }
    }
}

Installing this package