SwiftUI sheet() modals with custom size on iPad

Question

How can I control the preferred presentation size of a modal sheet on iPad with SwiftUI? I'm surprised how hard it is to find an answer on Google for this.

Also, what is the best way to know if the modal is dismissed by dragging it down (cancelled) or actually performing a custom positive action?

Answer 1

Here is my solution for showing a form sheet on an iPad in SwiftUI:

struct MyView: View {
    @State var show = false

    var body: some View {
        Button("Open Sheet") { self.show = true }
            .formSheet(isPresented: $show) {
                Text("Form Sheet Content")
            }
    }
}

Enabled by this UIViewControllerRepresentable

class FormSheetWrapper<Content: View>: UIViewController, UIPopoverPresentationControllerDelegate {

    var content: () -> Content
    var onDismiss: (() -> Void)?

    private var hostVC: UIHostingController<Content>?

    required init?(coder: NSCoder) { fatalError("") }

    init(content: @escaping () -> Content) {
        self.content = content
        super.init(nibName: nil, bundle: nil)
    }

    func show() {
        guard hostVC == nil else { return }
        let vc = UIHostingController(rootView: content())

        vc.view.sizeToFit()
        vc.preferredContentSize = vc.view.bounds.size

        vc.modalPresentationStyle = .formSheet
        vc.presentationController?.delegate = self
        hostVC = vc
        self.present(vc, animated: true, completion: nil)
    }

    func hide() {
        guard let vc = self.hostVC, !vc.isBeingDismissed else { return }
        dismiss(animated: true, completion: nil)
        hostVC = nil
    }

    func presentationControllerWillDismiss(_ presentationController: UIPresentationController) {
        hostVC = nil
        self.onDismiss?()
    }
}

struct FormSheet<Content: View> : UIViewControllerRepresentable {

    @Binding var show: Bool

    let content: () -> Content

    func makeUIViewController(context: UIViewControllerRepresentableContext<FormSheet<Content>>) -> FormSheetWrapper<Content> {

        let vc = FormSheetWrapper(content: content)
        vc.onDismiss = { self.show = false }
        return vc
    }

    func updateUIViewController(_ uiViewController: FormSheetWrapper<Content>,
                                context: UIViewControllerRepresentableContext<FormSheet<Content>>) {
        if show {
            uiViewController.show()
        }
        else {
            uiViewController.hide()
        }
    }
}

extension View {
    public func formSheet<Content: View>(isPresented: Binding<Bool>,
                                          @ViewBuilder content: @escaping () -> Content) -> some View {
        self.background(FormSheet(show: isPresented,
                                  content: content))
    }
}

You should be able to modify the code in func show() according to UIKit specs in order to get the sizing the way you like (and you can even go so far as to inject parameters from the SwiftUI side if needed). This is just how I get a form sheet to work on iPad as .sheet was just too big for my use case