Developing a Document-Based App in SwiftUI

ImageViewer.swift

import SwiftUI

struct ContentView: View {
    @ObservedObject var browser = { () -> DocumentBrowserObject in
        let dbo = DocumentBrowserObject (
            forOpeningFilesWithContentTypes: [
                "public.png",
                "public.jpeg"
            ]
        )
        return dbo
    }()
    
    @State var presenting = false
    
    var body: some View {
        ObservableControllerView(object: browser)
            .fullScreen(isPresented: $presenting) {
                DocumentView(url: self.browser.documentURLs.first)
            }
            .onReceive(browser.$documentURLs) { urls in
                if urls.isEmpty { return }
                if urls.count != 1 { fatalError() }
                self.presenting.toggle()
            }
    }
}

struct FullScreenModifier<IncomingView: View>: ViewModifier {
    @Binding var isPresented: Bool
    @State var content: () -> IncomingView
    func body(content: Content) -> some View {
        ZStack {
            content
            if isPresented {
                NavigationView {
                    self.content().navigationBarItems(leading:
                        Button(action: {
                            self.isPresented.toggle()
                        }) {
                            Text("Done")
                        }
                    )
                }
                .navigationViewStyle(StackNavigationViewStyle())
                .animation(.default)
                .transition(.move(edge:.bottom))
                .zIndex(1)
            }
        }
    }
}

extension View {
    public func fullScreen<Content: View> (
        isPresented: Binding<Bool>,
        content: @escaping () -> Content
    ) -> some View {
        modifier (
            FullScreenModifier(isPresented: isPresented, content: content)
        )
    }
}

class Document: UIDocument, ObservableObject {
    @Published var image = UIImage()
    
    override func load(fromContents contents: Any, ofType typeName: String?) throws {
        guard let data = contents as? Data else {
            fatalError()
        }
        guard let image = UIImage(data: data) else {
            fatalError()
        }
        self.image = image
    }
}

struct DocumentView: View {
    @ObservedObject var document: Document
    
    init(url: URL?) {
        guard let url = url else { fatalError() }
        document = Document(fileURL: url)
        document.open { guard $0 else { fatalError() } }
    }
    
    func done() {
        document.close { guard $0 else { fatalError() } }
    }
    
    var body: some View {
        Image(uiImage: document.image).onDisappear(perform: done)
    }
}

open class DocumentBrowserObject: UIDocumentBrowserViewController, ObservableObject {
    @Published open var documentURLs: [URL] = []
}

extension DocumentBrowserObject {
    open override func loadView() {
        super.loadView()
        delegate = self
    }
}

extension DocumentBrowserObject: UIDocumentBrowserViewControllerDelegate {
    open func documentBrowser(_ controller: UIDocumentBrowserViewController, didPickDocumentsAt documentURLs: [URL]) {
        self.documentURLs = documentURLs
    }
}

public struct ObservableControllerView: UIViewControllerRepresentable {
    public var uiViewController: UIViewController
    
    public init<ObservableController>(object: ObservableController) where ObservableController: UIViewController, ObservableController: ObservableObject {
        self.uiViewController = object
    }
    
    public func makeUIViewController(context: Self.Context) -> UIViewController {
        uiViewController
    }
    
    public func updateUIViewController(_ uiViewController: UIViewController, context: Self.Context) {
        //
    }
}

import PlaygroundSupport

PlaygroundPage.current.wantsFullScreenLiveView = true
PlaygroundPage.current.setLiveView(ContentView())