Custom size popover in iOS SwiftUI

WithPopover.swift

// -- Usage

struct Content: View {
    @State var open = false
    @State var popoverSize = CGSize(width: 300, height: 300)
    
    var body: some View {
        WithPopover(
            showPopover: $open,
            popoverSize: popoverSize,
            content: {
                Button(action: { self.open.toggle() }) {
                    Text("Tap me")
                }
        },
            popoverContent: {
                VStack {
                    Button(action: { self.popoverSize = CGSize(width: 300, height: 600)}) {
                        Text("Increase size")
                    }
                    Button(action: { self.open = false}) {
                        Text("Close")
                    }
                }
        })
    }
}


// -- Source

struct WithPopover<Content: View, PopoverContent: View>: View {
    
    @Binding var showPopover: Bool
    var popoverSize: CGSize? = nil
    let content: () -> Content
    let popoverContent: () -> PopoverContent
    
    var body: some View {
        content()
        .background(
            Wrapper(showPopover: $showPopover, popoverSize: popoverSize, popoverContent: popoverContent)
                .frame(maxWidth: .infinity, maxHeight: .infinity)
        )
    }
    
    struct Wrapper<PopoverContent: View> : UIViewControllerRepresentable {
        
        @Binding var showPopover: Bool
        let popoverSize: CGSize?
        let popoverContent: () -> PopoverContent
        
        func makeUIViewController(context: UIViewControllerRepresentableContext<Wrapper<PopoverContent>>) -> WrapperViewController<PopoverContent> {
            return WrapperViewController(
                popoverSize: popoverSize,
                popoverContent: popoverContent) {
                    self.showPopover = false
            }
        }
        
        func updateUIViewController(_ uiViewController: WrapperViewController<PopoverContent>,
                                    context: UIViewControllerRepresentableContext<Wrapper<PopoverContent>>) {
            uiViewController.updateSize(popoverSize)

            if showPopover {
                uiViewController.showPopover()
            }
            else {
                uiViewController.hidePopover()
            }
        }
    }
    
    class WrapperViewController<PopoverContent: View>: UIViewController, UIPopoverPresentationControllerDelegate {
        
        var popoverSize: CGSize?
        let popoverContent: () -> PopoverContent
        let onDismiss: () -> Void
        
        var popoverVC: UIViewController?

        required init?(coder: NSCoder) { fatalError("") }
        init(popoverSize: CGSize?,
             popoverContent: @escaping () -> PopoverContent,
             onDismiss: @escaping() -> Void) {
            self.popoverSize = popoverSize
            self.popoverContent = popoverContent
            self.onDismiss = onDismiss
            super.init(nibName: nil, bundle: nil)
        }
        
        override func viewDidLoad() {
            super.viewDidLoad()
        }
        
        func showPopover() {
            guard popoverVC == nil else { return }
            let vc = UIHostingController(rootView: popoverContent())
            if let size = popoverSize { vc.preferredContentSize = size }
            vc.modalPresentationStyle = UIModalPresentationStyle.popover
            if let popover = vc.popoverPresentationController {
                popover.sourceView = view
                popover.delegate = self
            }
            popoverVC = vc
            self.present(vc, animated: true, completion: nil)
        }
        
        func hidePopover() {
            guard let vc = popoverVC, !vc.isBeingDismissed else { return }
            vc.dismiss(animated: true, completion: nil)
            popoverVC = nil
        }
        
        func presentationControllerWillDismiss(_ presentationController: UIPresentationController) {
            popoverVC = nil
            self.onDismiss()
        }
        
        func updateSize(_ size: CGSize?) {
            self.popoverSize = size
            if let vc = popoverVC, let size = size {
                vc.preferredContentSize = size
            }
        }
    }
}

With iOS 16.4 - haven’t had a chance to test it myself but the new presentationCompactAdaptation(.none) modifier may work - Apples documentation - Apply the new .presentationCompactAdaptation(_:) modifier to the content of a modal presentation to control how it adapts to compact size classes on iPad and iPhone.
For example, the popover modifier presents a popover on iPad. By default, a popover adapts to the narrow horizontal size class on iPhone by showing as a sheet. In the example below, the .presentationCompactAdaptation(.none) modifier asks SwiftUI to show this as a popover on iPhone as well.
struct PopoverExample: View {
@State private var isShowingPopover = false

  var body: some View {
      Button("Show Popover") {
          self.isShowingPopover = true
      }
      .popover(isPresented: $isShowingPopover) {
          Text("Popover Content")
              .padding()
              .presentationCompactAdaptation(.none)
      }
  }

}
Use .presentationCompactAdaptation(horizontal:vertical:) to adapt differently in horizontally and vertically compact size classes. (103257577)

@INuvanda: Yes, there is this warning all the time and its getting worse with Xcode 15 beta: Here it's stated that this will be an error in future releases. I used these two nice extensions

extension UIWindow {
    static var key: UIWindow? {                                     // replacement of keyWindow
        if #available(iOS 13, *) {
                // from: https://stackoverflow.com/questions/57134259/how-to-resolve-keywindow-was-deprecated-in-ios-13-0
            return UIApplication
                .shared
                .connectedScenes
                .compactMap { $0 as? UIWindowScene }
                .flatMap { $0.windows }
                .last { $0.isKeyWindow }
        } else {
            return UIApplication.shared.keyWindow
        }
    }
}

extension UIViewController {
        // from https://stackoverflow.com/questions/26667009/get-top-most-uiviewcontroller
    static var topMostViewController: UIViewController? {
        var topMostViewController = UIWindow.key?.rootViewController    // the starting vc
        while let presentedViewController = topMostViewController?.presentedViewController {
            topMostViewController = presentedViewController         // loop over all presented vcs
        }
        return topMostViewController                                // and return the last/topmost one
    }
}

to modify the function showPopover():

        func showPopover() {
            guard popoverVC == nil,
            let topMostViewController = Self.topMostViewController else { return }
            let vc = UIHostingController(rootView: popoverContent())
            if let size = popoverSize { vc.preferredContentSize = size }
            vc.modalPresentationStyle = UIModalPresentationStyle.popover
            if let popover = vc.popoverPresentationController {
                popover.sourceView = view
                 popover.delegate = self
            }
            popoverVC = vc
            topMostViewController.present(vc, animated: true, completion: nil)    // present from topmost VC
        }

and the warning is gone.