Customize the annotation selection knobs in Swift for iOS

Customize the look of selected annotations by removing, repositioning and tinting the selection knobs. Get additional resources by visiting our PSPDFResizableViewOuterKnob API guide.

//
//  Copyright © 2016-2026 PSPDFKit GmbH. All rights reserved.
//
//  The Nutrient sample applications are licensed with a modified BSD license.
//  Please see License for details. This notice may not be removed from this file.
//


import PSPDFKit
import PSPDFKitUI


class SelectionKnobsExample: Example, PDFViewControllerDelegate {


    override init() {
        super.init()
        title = "Custom Selection Knobs Example"
        contentDescription = "Shows how to remove, reposition and style the selection knobs."
        category = .viewCustomization
    }


    override func invoke(with delegate: ExampleRunnerDelegate) -> UIViewController {
        let document = AssetLoader.document(for: .annualReport)


        // Add free text
        let freeText = FreeTextAnnotation()
        freeText.fontSize = 30
        freeText.contents = "I am example text. Drag me!"
        freeText.boundingBox = CGRect(x: 50, y: 250, width: 300, height: 300)
        freeText.sizeToFit()
        freeText.color = .blue
        freeText.absolutePageIndex = 0
        document.add(annotations: [freeText])


        let pdfController = PDFViewController(document: document, delegate: self) {
            $0.overrideClass(ResizableView.self, with: OnePointResizableView.self)
        }


        let appearance = ResizableView.appearance()
        appearance.selectionBorderWidth = 3
        appearance.cornerRadius = 6


        return pdfController
    }


    // MARK: PDFViewControllerDelegate


    internal func pdfViewController(_ pdfController: PDFViewController, didConfigurePageView pageView: PDFPageView, forPageAt pageIndex: Int) {
        if pageView.pageIndex == 0 {
            pageView.selectedAnnotations = pdfController.document?.annotationsForPage(at: 0, type: .freeText)
        }
    }


    // MARK: - Resizable view customization


    class OnePointResizableView: ResizableView {


        // MARK: Lifecycle


        override init(frame: CGRect) {
            super.init(frame: frame)
            removeAndTintKnobs()
        }


        required init?(coder aDecoder: NSCoder) {
            super.init(coder: aDecoder)
            removeAndTintKnobs()
        }


        // MARK: Knob customization


        func removeAndTintKnobs() {
            // Remove all knobs but the bottom right one.
            let unwantedKnobs: [OuterKnob] = [.topLeft, .topMiddle, .topRight, .middleLeft, .middleRight, .bottomLeft, .bottomMiddle]
            for knobType in unwantedKnobs {
                // `outerKnob(ofType:)` will only return nil if passed the type `.unknown`.
                outerKnob(ofType: knobType)!.removeFromSuperview()
            }
            // Use a custom tint color.
            tintColor = UIColor(red: 1, green: 0.622, blue: 0, alpha: 1)
        }


        override func centerPoint(for knobType: ResizableView.OuterKnob, inFrame frame: CGRect) -> CGPoint {
            var point = super.centerPoint(for: knobType, inFrame: frame)
            if knobType == .bottomRight {
                point.x += 10
                point.y += 10
            }
            return point
        }


        override func newKnobView(for type: KnobType) -> UIView & KnobView {
            return SquareKnobView(type: type)
        }
    }


    // MARK: - Custom knob view


    class SquareKnobView: UIView, KnobView {


        // MARK: Lifecycle


        convenience init(type: KnobType) {
            self.init()
            self.type = type
            frame = CGRect(origin: CGPoint.zero, size: knobSize)
            setUpShape()
        }


        // MARK: View


        override var bounds: CGRect {
            didSet {
                updatePaths()
            }
        }


        override func tintColorDidChange() {
            super.tintColorDidChange()
            updateColors()
        }


        // MARK: Layer


        override class var layerClass: AnyClass {
            return CAShapeLayer.self
        }


        var shapeLayer: CAShapeLayer {
            return layer as! CAShapeLayer
        }


        func setUpShape() {
            let layer = shapeLayer
            layer.strokeColor = UIColor.white.cgColor
            layer.shadowColor = UIColor.black.cgColor
            layer.shadowOffset = CGSize(width: 0, height: 1)
            layer.shadowOpacity = 0.4
            layer.shadowRadius = 1
            updateColors()
        }


        func updateColors() {
            let layer = shapeLayer
            layer.fillColor = tintColor.cgColor
            layer.strokeColor = UIColor(white: type == .outer ? 1 : 0.9, alpha: 1).cgColor
        }


        func updatePaths() {
            // The bounds change when zooming. Keep the dimensions proportional
            // to bounds to end up with the same apparent size.
            let width = min(bounds.width, bounds.height) / 6.0
            let layer = shapeLayer
            layer.path = UIBezierPath(roundedRect: bounds, cornerRadius: width).cgPath
            layer.shadowPath = layer.path
            layer.lineWidth = width
        }


        // MARK: PSPDFKnobView


        var type = KnobType.outer {
            didSet {
                updateColors()
            }
        }


        let knobSize = CGSize(width: 12, height: 12)
    }
}

This code sample is an example that illustrates how to use our SDK. Please adapt it to your specific use case.