Enable Auto-Save in PDF using Swift for iOS

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//
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//  Copyright © 2017-2025 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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/// Simple example to demonstrate how checkpointing works.
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class DocumentCheckpointingExample: Example {
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    override init() {
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        super.init()
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        title = "Document Checkpointing"
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        contentDescription = "Demonstrates use of document checkpointing API"
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        category = .annotations
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        priority = 2000
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    }
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    private var annotatedDocument: Document?
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    private var checkpointObserver: NSObjectProtocol?
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    override func invoke(with delegate: ExampleRunnerDelegate) -> UIViewController? {
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        let document = AssetLoader.writableDocument(for: AssetName.about, overrideIfExists: true)
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        // Checkpoint the document as soon as the annotation is added.
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        document.checkpointer.strategy = .immediate
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        let pdfController = PDFViewController()
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        checkpointObserver = NotificationCenter.default.addObserver(forName: .PSPDFDocumentCheckpointSaved, object: document.checkpointer, queue: OperationQueue.main) { [weak self] _ in
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            if let observer = self?.checkpointObserver {
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                NotificationCenter.default.removeObserver(observer)
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            }
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            // In practice, you would always want to use this initialiser when creating documents that may have been changed by the user.
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            let documentWithCheckpoint = Document(dataProviders: [CoordinatedFileDataProvider(fileURL: document.fileURL!)], loadCheckpointIfAvailable: true)
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            pdfController.document = documentWithCheckpoint
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            // At this point, the document is not saved, but still has the annotation.
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            // Calling Document.save() will save the annotations restored from the checkpoint to the document.
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            NSLog("Annotation from checkpoint: \(document.allAnnotations(of: .square))")
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        }
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        let annotation = SquareAnnotation()
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        annotation.boundingBox = CGRect(x: 20, y: 200, width: 100, height: 100)
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        annotation.fillColor = .red
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        DispatchQueue.main.asyncAfter(deadline: .now() + 0.5) {
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            // Add the annotation to the document.
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            document.add(annotations: [annotation])
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        }
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        return pdfController
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    }
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}