Using a Custom Annotation Provider in Swift 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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class AnnotationProviderWithRotationExample: Example {
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    override init() {
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        super.init()
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        title = "Custom Annotation Provider With Serialization and Rotation"
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        contentDescription = "A custom annotation provider that serializes its annotations shown working with temporary page rotations."
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        category = .annotationProviders
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    }
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    override func invoke(with delegate: ExampleRunnerDelegate) -> UIViewController {
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        let document = AssetLoader.document(for: AssetName.welcome)
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        document.didCreateDocumentProviderBlock = { documentProvider in
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            let cachesDirectory = FileManager.default.urls(for: .cachesDirectory, in: .userDomainMask).first!
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            let dataDirectory = cachesDirectory.appendingPathComponent("AnnotationProviderWithRotationExample", isDirectory: true)
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            try! FileManager.default.createDirectory(at: dataDirectory, withIntermediateDirectories: true, attributes: nil)
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            let storageURL = dataDirectory.appendingPathComponent("\(document.uid!).annotations", isDirectory: false)
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            let customProvider = AnnotationProvider(storageFileURL: storageURL, documentProvider: documentProvider)
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            // Include the default file annotation provider so it can load links and form elements from the PDF.
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            let fileAnnotationProvider = documentProvider.annotationManager.fileAnnotationProvider!
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            documentProvider.annotationManager.annotationProviders = [customProvider, fileAnnotationProvider]
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        }
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        return RotatePageTemporarilyExample.RotatePagePDFViewController(document: document) {
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            $0.pageMode = .single
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        }
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    }
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    /// A custom annotation provider that loads from, and saves to, a file.
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    ///
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    /// This is only useful as an example. In practice this technique is for when you have a custom annotation backend
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    /// such as a database. If you just want to save annotations to an external file in an archive, do not use a custom
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    /// annotation provider and instead set the document’s `annotationSaveMode` to `PSPDFAnnotationSaveModeExternalFile`.
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    private class AnnotationProvider: PDFContainerAnnotationProvider {
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        let storageFileURL: URL
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        init(storageFileURL: URL, documentProvider: PDFDocumentProvider) {
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            self.storageFileURL = storageFileURL
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            super.init(documentProvider: documentProvider)
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            guard let data = try? Data(contentsOf: storageFileURL) else {
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                // Most likely the file does not exist. Don’t care.
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                return
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            }
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            let annotations = try! NSKeyedUnarchiver.unarchivedObject(ofClasses: [NSArray.self, Annotation.self], from: data)
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            // We don’t want to post any notifications here: there can’t be anyone listening and nothing changed.
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            super.add(annotations as! [Annotation], options: [.suppressNotifications: true])
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            performWrite {
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                // Adding the annotations may set the save flag but nothing actually changed => Clear the flag.
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                self.clearNeedsSaveFlag()
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            }
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        }
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        override func saveAnnotations(options: [String: Any]? = nil) throws {
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            let data = try NSKeyedArchiver.archivedData(withRootObject: allAnnotations as NSArray, requiringSecureCoding: true)
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            try data.write(to: storageFileURL)
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            performWriteAndWait {
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                clearNeedsSaveFlag()
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            }
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        }
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    }
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}