Enable saving confirmation when exiting PDF in Swift for iOS

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//
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//  Copyright © 2017-2026 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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class SavePermissionExample: Example, PDFViewControllerDelegate {
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    override init() {
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        super.init()
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        title = "Save permission alert before closing"
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        category = .annotations
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        priority = 400
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    }
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    override func invoke(with delegate: ExampleRunnerDelegate) -> UIViewController {
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        let document = AssetLoader.writableDocument(for: .welcome, overrideIfExists: false)
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        /*
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         Note: Having auto saving of a document disabled and asking to save before exiting isn't a 100% reliable approach on iOS approach, since the app can always be closed using the multitasking switcher, where this action will not be called, resulting in loss of the made changes.
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         */
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        let controller = SavePermissionViewController(document: document) {
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            // Disable autosaving of the PDF.
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            $0.isAutosaveEnabled = false
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        }
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        return controller
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    }
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}
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private class SavePermissionViewController: PDFViewController {
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    override func commonInit(with document: Document?, configuration: PDFConfiguration) {
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        super.commonInit(with: document, configuration: configuration)
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        let exitButton = UIBarButtonItem(title: "Exit", style: .done, target: self, action: #selector(exit))
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        // Add custom exit button that shows the alert controller when tapped
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        self.navigationItem.leftBarButtonItems = [exitButton]
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    }
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    @objc func exit() {
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        // Check if the document has any changes or not. Exit immediately if it doesn't.
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        guard let document = self.document, document.hasDirtyAnnotations == true else {
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            _ = self.navigationController?.popViewController(animated: true)
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            return
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        }
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        let alertController = UIAlertController(title: nil, message: "Do you want to save the changes made to the document?", preferredStyle: .alert)
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        let saveAction = UIAlertAction(title: "Save", style: .default) { _ in
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            guard let document = self.document else { return }
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            // Manually save the document and exit after saving
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            document.save { _ in
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                self.navigationController?.popViewController(animated: true)
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            }
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        }
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        let exitAction = UIAlertAction(title: "Exit without save", style: .destructive) { _ in
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            // Clear document cache when discarding unsaved changes.
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            // This is required when not saving changes
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            // to prevent stale cached renders from appearing when the document is reopened.
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            SDK.shared.cache.remove(for: document)
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            self.navigationController?.popViewController(animated: true)
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        }
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        let cancelAction = UIAlertAction(title: "Cancel", style: .cancel)
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        alertController.addAction(exitAction)
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        alertController.addAction(saveAction)
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        alertController.addAction(cancelAction)
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        self.present(alertController, animated: true, completion: nil)
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    }
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}