Show author name on annotation selection in Swift for iOS

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//
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//  Copyright © 2020-2026 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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/// Example that adds a custom overlaying view to the `PDFPageView` when a user selects an annotation.
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class ShowAuthorNameOnAnnotationSelectionExample: Example {
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    override init() {
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        super.init()
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        category = .viewCustomization
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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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        let controller = CustomOverlayingViewViewController(document: document)
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        // Add annotation interaction hooks to display author name.
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        controller.addAnnotationInteractionActions()
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        // Show a page with annotations.
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        controller.pageIndex = 15
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        return controller
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    }
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}
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/// `PDFViewController` subclass that can add actions to be executed on a user interaction with annotations.
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private class CustomOverlayingViewViewController: PDFViewController {
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    /// Currently visible overlaying view.
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    var displayingCustomOverlayView: CustomOverlayLabelView?
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    /// Adds the actions to be executed whenever the user selects or de-selects an annotation.
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    func addAnnotationInteractionActions() {
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        // `selectAnnotation.addActivationCallback` code block is called whenever a user selects an annotation.
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        self.interactions.selectAnnotation.addActivationCallback { context, _, _  in
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            // Use the provided context to get the page and annotation about to be selected.
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            let selectedAnnotation = context.annotation
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            let authorName = selectedAnnotation.user ?? "Unknown Author"
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            let pageView = context.pageView
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            // `boundingBox` is in the page coordinates that is in the PDF coordinate space which means
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            // origin is at the bottom left.
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            // For more info: https://www.nutrient.io/guides/ios/faq/coordinate-spaces/
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            let selectedAnnotationBoundingBox = selectedAnnotation.boundingBox
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            // We anchor the custom overlay view at the centre of the annotation.
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            let viewSize: CGFloat = 40
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            let authorViewRect = CGRect(x: selectedAnnotationBoundingBox.midX - (viewSize / 2), y: selectedAnnotationBoundingBox.midY - (viewSize / 2), width: viewSize, height: viewSize)
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            let authorView = CustomOverlayLabelView(authorName: authorName, pageView: pageView, pdfRect: authorViewRect)
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            // Add the custom overlay view to the page view.
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            pageView.addSubview(authorView)
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            // Remove the existing author view in case the current annotation is selected without
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            // de-selecting the earlier annotation
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            self.displayingCustomOverlayView?.removeFromSuperview()
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            // Store a reference to the author view to remove it from the view when an annotation is
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            // deselected.
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            self.displayingCustomOverlayView = authorView
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        }
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        // `deselectAnnotation.addActivationCallback` code block is called whenever a user de-selects an annotation.
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        self.interactions.deselectAnnotation.addActivationCallback { _, _, _ in
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            // Remove the view as the annotation is no longer in selection.
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            self.displayingCustomOverlayView?.removeFromSuperview()
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        }
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    }
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}
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/// A view containing a `UILabel` that can be added to a `PDFPageView`.
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private class CustomOverlayLabelView: UIView {
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    let pdfRect: CGRect
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    weak var pageView: PDFPageView?
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    let authorLabel: UILabel = {
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        let label = UILabel()
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        label.translatesAutoresizingMaskIntoConstraints = false
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        return label
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    }()
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    /// Creates and returns a view that contains a label that can be added to a `PDFPageView`.
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    /// - Parameters:
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    ///   - authorName: Text to be displayed in the contained label.
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    ///   - pageView: Page view to which this view is added.
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    ///   - pdfRect: `CGRect` in PDF Page coordinates where the custom view is supposed to be placed.
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    ///   Will be converted to the `pageView`'s coordinate space before using it as the `frame`.
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    init(authorName: String, pageView: PDFPageView, pdfRect: CGRect) {
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        self.pageView = pageView
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        self.pdfRect = pdfRect
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        // Convert the rect from PDF Page Coordinates to PageView coordinates.
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        let viewRect = pageView.convert(pdfRect, from: pageView.pdfCoordinateSpace)
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        super.init(frame: viewRect)
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        addSubview(authorLabel)
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        NSLayoutConstraint.activate([
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            authorLabel.centerXAnchor.constraint(equalTo: centerXAnchor),
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            authorLabel.centerYAnchor.constraint(equalTo: centerYAnchor)
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        ])
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        authorLabel.text = authorName
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        // Use black text color here because the page background is light
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        // and to ensure the text visibility in both light and dark mode.
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        authorLabel.textColor = .black
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    }
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    required init?(coder: NSCoder) {
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        fatalError("init(coder:) has not been implemented")
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    }
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}