Add overlay views to PDF in Swift for iOS

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//
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//  Copyright © 2021-2026 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 OverlayViewsExample: Example, PDFViewControllerDelegate {
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    override init() {
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        super.init()
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        title = "Adding Overlay Views"
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        contentDescription = "Shows how to add custom overlay views on top of pages."
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        category = .controllerCustomization
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        priority = 40
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    }
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    override func invoke(with delegate: ExampleRunnerDelegate) -> UIViewController? {
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        PDFViewController(document: AssetLoader.document(for: .annualReport), delegate: self) { builder in
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            builder.maximumZoomScale = 20
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        }
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    }
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    func pdfViewController(_ pdfController: PDFViewController, didConfigurePageView pageView: PDFPageView, forPageAt pageIndex: Int) {
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        // This is the size pf page and overlay in PDF coordinate space.
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        // See: https://www.nutrient.io/guides/ios/faq/coordinate-spaces/
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        guard let pageSize = pageView.pageInfo?.size else { return }
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        let overlaySize = CGSize(width: 30, height: 30)
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        // Add 4 custom views at the 4 corners of the first page. Nutrient will
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        // reuse the page view but in doing so it will clear all foreign views,
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        // so you don't have to remove them yourself.
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        guard pageView.pageIndex == 0 else { return }
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        // Top-left is actually "bottom-left" in PDF coordinates.
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        let topLeftBoundingBox = CGRect(x: 0, y: pageSize.height - overlaySize.height, width: overlaySize.width, height: overlaySize.height)
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        let topLeftView = OverlayView(on: pageView, boundingBox: topLeftBoundingBox, color: .yellow)
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        pageView.annotationContainerView.addSubview(topLeftView)
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        // Top-right is actually "bottom-right" in PDF coordinates.
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        let topRightBoundingBox = CGRect(x: pageSize.width - overlaySize.width, y: pageSize.height - overlaySize.height, width: overlaySize.width, height: overlaySize.height)
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        let topRightView = OverlayView(on: pageView, boundingBox: topRightBoundingBox, color: .red)
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        pageView.annotationContainerView.addSubview(topRightView)
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        // Bottom-right is actually "top-right" in PDF coordinates.
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        let bottomRightBoundingBox = CGRect(x: pageSize.width - overlaySize.width, y: 0, width: overlaySize.width, height: overlaySize.height)
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        let bottomRightView = OverlayView(on: pageView, boundingBox: bottomRightBoundingBox, color: .green)
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        pageView.annotationContainerView.addSubview(bottomRightView)
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        // Bottom-left is actually "top-left" in PDF coordinates.
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        let bottomLeftBoundingBox = CGRect(origin: .zero, size: overlaySize)
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        let bottomLeftView = OverlayView(on: pageView, boundingBox: bottomLeftBoundingBox, color: .blue)
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        pageView.annotationContainerView.addSubview(bottomLeftView)
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    }
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}
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private class OverlayView: UIView, AnnotationPresenting {
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    init(on pageView: PDFPageView, boundingBox: CGRect, color backgroundColor: UIColor) {
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        self.pageView = pageView
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        self.boundingBox = boundingBox
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        super.init(frame: .zero)
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        self.backgroundColor = backgroundColor
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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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    weak var pageView: PDFPageView?
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    private let boundingBox: CGRect
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    override func didMoveToSuperview() {
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        super.didMoveToSuperview()
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        // Update the frame when this view is first added to the hierarchy.
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        updateFrameBasedOnBoundingBox()
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    }
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    func didChangePageBounds(_ bounds: CGRect) {
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        // Update the frame once the page rotates.
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        updateFrameBasedOnBoundingBox()
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    }
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    private func updateFrameBasedOnBoundingBox() {
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        guard let pageView, let superview else { return }
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        frame = superview.convert(boundingBox, from: pageView.pdfCoordinateSpace)
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    }
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}