Monitor UI Touches using Swift for iOS

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//
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//  Copyright © 2018-2025 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 TouchMonitorExample: Example, UIGestureRecognizerDelegate {
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    private weak var pdfController: PDFViewController?
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    private weak var highlightView: UILabel?
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    override init() {
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        super.init()
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        title = "Monitor touches"
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        contentDescription = "Shows how to get a callback when the user touches anywhere in the PDFViewController's view."
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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.document(for: .welcome)
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        let pdfController = PDFViewController(document: document)
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        let gestureRecognizer = UILongPressGestureRecognizer(target: self, action: #selector(touchReceived(_:)))
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        gestureRecognizer.delaysTouchesBegan = false
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        gestureRecognizer.delaysTouchesEnded = false
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        gestureRecognizer.cancelsTouchesInView = false
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        gestureRecognizer.delegate = self
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        gestureRecognizer.minimumPressDuration = 0.0
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        pdfController.view.addGestureRecognizer(gestureRecognizer)
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        self.pdfController = pdfController
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        return pdfController
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    }
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    // MARK: Gesture Recognizer Delegate
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    func gestureRecognizer(_ gestureRecognizer: UIGestureRecognizer, shouldRecognizeSimultaneouslyWith otherGestureRecognizer: UIGestureRecognizer) -> Bool {
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        return true
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    }
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    // MARK: Actions
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    @objc func touchReceived(_ gesture: UIGestureRecognizer) {
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        guard gesture.state == .began else { return }
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        if highlightView == nil {
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            guard let view = pdfController?.view else { return }
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            let label = UILabel()
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            label.text = "Touch detected."
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            label.backgroundColor = UIColor.systemRed
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            label.font = UIFont.systemFont(ofSize: 40.0)
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            label.translatesAutoresizingMaskIntoConstraints = false
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            view.addSubview(label)
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            NSLayoutConstraint.activate([
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                label.centerXAnchor.constraint(equalTo: view.centerXAnchor),
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                label.centerYAnchor.constraint(equalTo: view.centerYAnchor),
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            ])
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            highlightView = label
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        }
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        guard let highlightView else { fatalError("The highlight view should have been created.") }
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        highlightView.alpha = 1.0
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        UIView.animate(withDuration: 0.5, delay: 0.3, options: [], animations: {
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            highlightView.alpha = 0.0
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        }, completion: nil)
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    }
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}