PDF Streaming withSwiftUI for iOS

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//
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//  Copyright © 2019-2025 PSPDFKit GmbH. All rights reserved.
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//
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//  The Nutrient sample applications are licensed with a modified BSD license.
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//  Please see License for details. This notice may not be removed from this file.
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//
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import PSPDFKit
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import PSPDFKitUI
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import SwiftUI
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/// The streaming document example can download documents on a page-by-page basis,
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/// so opening is pretty much instant.
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///
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/// Please see the header comment of `StreamingDocumentExample` for a list of caveats.
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class StreamingDocumentSwiftUIExample: Example {
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    override init() {
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        super.init()
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        title = "SwiftUI Streaming a document on-demand from a web-server"
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        contentDescription = "Demonstrates a way to load parts of a document on demand in SwiftUI."
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        category = .swiftUI
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        priority = 20
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    }
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    override func invoke(with delegate: ExampleRunnerDelegate) -> UIViewController? {
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        let streamingHelper = StreamingDocumentGenerator()
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        let streamingDocument = streamingHelper.streamingDocument
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        let swiftUIView = SwiftUIStreamingDocumentExampleView(streamingDocument: streamingDocument)
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        let hostingController = UIHostingController(rootView: swiftUIView, largeTitleDisplayMode: .never)
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        streamingHelper.showExampleAlertIfNeeded(on: hostingController)
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        return hostingController
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    }
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}
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final class SwiftUIStreamingDocumentExampleViewModel: ObservableObject {
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    @Published var document: StreamingDocument
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    // We need the internal wrapped view controller to update individual pages
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    weak var controller: PDFViewController?
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    init(fetchableDocument: StreamingDocument) {
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        self.document = fetchableDocument
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    }
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}
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private struct SwiftUIStreamingDocumentExampleView: View {
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    @ObservedObject var viewModel: SwiftUIStreamingDocumentExampleViewModel
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    @PDFView.Scope private var scope
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    init(streamingDocument: StreamingDocument) {
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        viewModel = SwiftUIStreamingDocumentExampleViewModel(fetchableDocument: streamingDocument)
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    }
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    var body: some View {
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        PDFView(document: viewModel.document)
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            .pageMode(.automatic)
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            .spreadFitting(.fill)
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            .pageLabelEnabled(false)
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            .thumbnailBarMode(.scrollable)
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            .updateConfiguration { builder in
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                builder.overrideClass(PDFViewController.self, with: StreamingPDFViewController.self)
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                builder.overrideClass(PDFPageView.self, with: StreamingPageView.self)
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                // These are optional, only if you need streaming thumbnails.
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                builder.overrideClass(ThumbnailBar.self, with: StreamingThumbnailBar.self)
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                builder.overrideClass(ThumbnailViewController.self, with: StreamingThumbnailViewController.self)
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            }
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            .updateControllerConfiguration { controller in
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                viewModel.controller = controller
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            }
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            .onDidDismiss { controller in
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                guard let streamingController = controller as? StreamingPDFViewController else { return }
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                streamingController.stopDownloadingFiles()
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            }
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            .toolbar {
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                DefaultToolbarButtons()
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                ToolbarItemGroup(placement: .topBarLeading) {
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                    Button("Clear Cache") {
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                        guard let streamingController = viewModel.controller as? StreamingPDFViewController else { return }
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                        SDK.shared.cache.clear()
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                        do {
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                            let downloadFolderURL = viewModel.document.streamingDefinition.downloadFolder
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                            if FileManager.default.fileExists(atPath: downloadFolderURL.path) {
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                                try FileManager.default.removeItem(at: viewModel.document.streamingDefinition.downloadFolder)
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                            }
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                            // Create a new document to force reload the file download status.
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                            let document = StreamingDocument(streamingDefinition: viewModel.document.streamingDefinition)
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                            streamingController.document = document
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                            viewModel.document = document
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                            streamingController.downloadFile(pageIndex: 0)
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                        } catch {
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                            print("Error occured clearing the streaming document download folder: \(error.localizedDescription)")
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                        }
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                    }
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                }
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            }
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            .pdfViewScope(scope)
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    }
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}