Highlight Text in PDF using Swift for iOS

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//
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//  Copyright © 2021-2025 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 BooksHighlightingExample: Example {
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    override init() {
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        super.init()
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        title = "Create Highlights From Selected Text"
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        contentDescription = "Shows how to automatically create a highlight annotation after selecting text."
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        category = .controllerCustomization
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        priority = 25
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    }
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    override func invoke(with delegate: ExampleRunnerDelegate) -> UIViewController? {
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        CustomPDFViewController(document: AssetLoader.writableDocument(for: .psychologyResearch, overrideIfExists: true))
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    }
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}
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private class CustomPDFViewController: PDFViewController, UIGestureRecognizerDelegate {
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    override func commonInit(with document: Document?, configuration: PDFConfiguration) {
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        super.commonInit(with: document, configuration: configuration.configurationUpdated { builder in
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            // Disable the menu that allows to create annotations.
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            builder.isCreateAnnotationMenuEnabled = false
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        })
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        // Remove annotationButtonItem since we only want highlight annotations,
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        // and these are created without going into special mode.
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        navigationItem.setRightBarButtonItems([thumbnailsButtonItem, activityButtonItem, outlineButtonItem, searchButtonItem], for: .document, animated: false)
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        // Enable the highlighting mode for Apple Pencil.
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        annotationStateManager.state = .highlight
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        annotationStateManager.stylusMode = .stylus
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    }
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    override func viewDidLoad() {
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        super.viewDidLoad()
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        // Add a custom gesture recognizer so that we can independently track
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        // when a touch begins and ends.
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        let recognizer = UILongPressGestureRecognizer(target: self, action: #selector(longPressGestureRecognizerDidChangeState))
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        recognizer.minimumPressDuration = 0
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        recognizer.delegate = self
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        view.addGestureRecognizer(recognizer)
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    }
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    // A flag that tells whether we're tracking a fresh text selection or not.
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    private var isFreshSelection = false
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    func gestureRecognizer(_ gestureRecognizer: UIGestureRecognizer, shouldRecognizeSimultaneouslyWith otherGestureRecognizer: UIGestureRecognizer) -> Bool {
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        // Let our gesture recognizer work "in background" and not interfere
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        // with any other gesture recognizer.
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        true
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    }
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    @objc private func longPressGestureRecognizerDidChangeState(_ recognizer: UILongPressGestureRecognizer) {
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        // Don't process touches outside of page views.
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        guard let pageView = documentViewController?.visiblePageView(at: recognizer.location(in: documentViewController?.view)) else {
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            return
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        }
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        // Track when a new text selection begins.
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        if recognizer.state == .began {
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            isFreshSelection = pageView.selectionView.selectedGlyphs.isEmpty
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            return
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        }
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        // Make sure that we're tracking a fresh text selection.
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        if recognizer.state == .ended, isFreshSelection, !pageView.selectionView.selectedGlyphs.isEmpty {
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            // Create a highlight annotation.
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            let highlight = HighlightAnnotation.textOverlayAnnotation(with: pageView.selectionView.selectedGlyphs)!
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            highlight.pageIndex = pageView.pageIndex
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            document?.add(annotations: [highlight])
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            // Wait until touch processing completes in the event loop cycle.
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            // Modifying selection directly in this method, while Nutrient is
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            // still processing touches internally, will lead to bad behavior.
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            DispatchQueue.main.async {
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                pageView.select(annotations: [highlight], presentMenu: true, animated: true)
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            }
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        }
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    }
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}