Create PDF Teleprompter 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 TeleprompterExample: Example {
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    override init() {
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        super.init()
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        title = "Teleprompter example"
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        category = .subclassing
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        priority = 30
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    }
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    override func invoke(with delegate: ExampleRunnerDelegate?) -> UIViewController {
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        let document = AssetLoader.document(for: .annualReport)
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        let pdfViewController = AutoScrollPDFViewController(document: document)
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        return pdfViewController
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    }
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}
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class PauseAutoScrollGestureRecognizer: UIGestureRecognizer {
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    override init(target: Any?, action: Selector?) {
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        super.init(target: target, action: action)
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            cancelsTouchesInView = false
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    }
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    override func touchesBegan(_ touches: Set<UITouch>, with event: UIEvent) {
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        if touches.count != 1 {
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            state = .failed
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            return
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        }
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        state = .began
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    }
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    override func touchesEnded(_ touches: Set<UITouch>, with event: UIEvent) {
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        state = .ended
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    }
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}
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private class AutoScrollPDFViewController: PDFViewController, UIGestureRecognizerDelegate {
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    var scrollTimer: Timer?
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    var pauseAutoScrollGestureRecognizer: PauseAutoScrollGestureRecognizer?
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    var scrollingPaused = false
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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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        updateConfiguration(builder: { builder in
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            builder.pageTransition = .scrollContinuous
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            builder.scrollDirection = .vertical
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            })
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    }
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    override func viewDidLoad() {
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        super.viewDidLoad()
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        pauseAutoScrollGestureRecognizer = PauseAutoScrollGestureRecognizer(target: self, action: #selector(handlePauseAutoScroll(_:)))
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        pauseAutoScrollGestureRecognizer?.delegate = self
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        if let pauseAutoScrollGestureRecognizer {
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            documentViewController?.view.addGestureRecognizer(pauseAutoScrollGestureRecognizer)
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        }
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    }
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    override func viewDidAppear(_ animated: Bool) {
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        super.viewDidAppear(animated)
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        scrollTimer = Timer.scheduledTimer(timeInterval: 0.01, target: self, selector: #selector(scroll), userInfo: nil, repeats: true)
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    }
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    override func viewWillDisappear(_ animated: Bool) {
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        super.viewWillDisappear(animated)
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        scrollTimer?.invalidate()
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        scrollTimer = nil
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    }
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    @objc func scroll() {
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        if scrollingPaused {
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            return
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        }
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        guard let documentViewController else { return }
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        // The layout object knows how many spreads we currently have:
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        let numberOfSpreads = documentViewController.layout.numberOfSpreads
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        let lastSpreadIndex = CGFloat(numberOfSpreads > 0 ? numberOfSpreads - 1 : 0)
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        // We scroll by updating the continuous spread index as long as we can:
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        let continuousSpreadIndex: CGFloat = documentViewController.continuousSpreadIndex + 0.001
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        if continuousSpreadIndex <= lastSpreadIndex {
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            documentViewController.continuousSpreadIndex = continuousSpreadIndex
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        }
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    }
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    @objc func handlePauseAutoScroll(_ tapGestureRecognizer: UITapGestureRecognizer?) {
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        if tapGestureRecognizer?.state == .began {
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            scrollingPaused = true
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        }
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        if tapGestureRecognizer?.state == .ended {
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            scrollingPaused = false
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        }
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    }
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    func gestureRecognizer(_ gestureRecognizer: UIGestureRecognizer, shouldRecognizeSimultaneouslyWith otherGestureRecognizer: UIGestureRecognizer) -> Bool {
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        // We'll ignore long presses but allow everything else, such as scrolling.
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        if gestureRecognizer == pauseAutoScrollGestureRecognizer && (otherGestureRecognizer is UILongPressGestureRecognizer) {
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            return false
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        }
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        return true
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    }
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}