3D touch/Force touch implementation

Question

How can we implement 3D touch to check if the user taps on UIView or force touch on UIView?

Is there a way to do this with UIGestureRecognize or only with UITouch?

Answer 1

You can do it without a designated gesture recognizer. You do not need to adjust the touchesEnded and touchesBegan method, but simply the touchesMoved to obtain the correct values. getting the force of a uitouch from began/ended will return weird values.

UITouch *touch = [touches anyObject];

CGFloat maximumPossibleForce = touch.maximumPossibleForce;
CGFloat force = touch.force;
CGFloat normalizedForce = force/maximumPossibleForce;

then, set a force threshold and compare the normalizedForce to this threshold (0.75 seems fine for me).

Answer 2

The 3D Touch properties are available on UITouch objects.

You can get these touches by overriding a UIView's touchesBegan: and touchesMoved: methods. Not sure what you see in touchesEnded: yet.

If you're willing to create new gesture recognizers, you have full access to the UITouches as exposed in UIGestureRecognizerSubclass.

I'm not sure how you could use the 3D touch properties in a traditional UIGestureRecognizer. Maybe via the UIGestureRecognizerDelegate protocol's gestureRecognizer:shouldReceiveTouch: method.

Answer 3

With Swift 4.2 and iOS 12, a possible way to solve your problem is to create a custom subclass of UIGestureRecognizer that handles Force Touch and add it to your view next to a UITapGestureRecognizer. The following complete code shows how to implement it:

ViewController.swift

import UIKit

class ViewController: UIViewController {

    let redView = UIView()
    lazy var tapGestureRecognizer = UITapGestureRecognizer(target: self, action: #selector(tapHandler))
    lazy var forceTouchGestureRecognizer = ForceTouchGestureRecognizer(target: self, action: #selector(forceTouchHandler))

    override func viewDidLoad() {
        super.viewDidLoad()

        redView.backgroundColor = .red    
        redView.addGestureRecognizer(tapGestureRecognizer)

        view.addSubview(redView)
        redView.translatesAutoresizingMaskIntoConstraints = false
        redView.centerXAnchor.constraint(equalTo: view.centerXAnchor).isActive = true
        redView.centerYAnchor.constraint(equalTo: view.centerYAnchor).isActive = true
        redView.widthAnchor.constraint(equalToConstant: 100).isActive = true
        redView.heightAnchor.constraint(equalToConstant: 100).isActive = true
    }

    override func traitCollectionDidChange(_ previousTraitCollection: UITraitCollection?) {
        super.traitCollectionDidChange(previousTraitCollection)

        if traitCollection.forceTouchCapability == UIForceTouchCapability.available {
            redView.addGestureRecognizer(forceTouchGestureRecognizer)
        } else  {
            // When force touch is not available, remove force touch gesture recognizer.
            // Also implement a fallback if necessary (e.g. a long press gesture recognizer)
            redView.removeGestureRecognizer(forceTouchGestureRecognizer)
        }
    }

    @objc func tapHandler(_ sender: UITapGestureRecognizer) {
        print("Tap triggered")
    }

    @objc func forceTouchHandler(_ sender: ForceTouchGestureRecognizer) {
        UINotificationFeedbackGenerator().notificationOccurred(.success)
        print("Force touch triggered")
    }

}

ForceTouchGestureRecognizer.swift

import UIKit.UIGestureRecognizerSubclass

@available(iOS 9.0, *)
final class ForceTouchGestureRecognizer: UIGestureRecognizer {

    private let threshold: CGFloat = 0.75

    override func touchesBegan(_ touches: Set<UITouch>, with event: UIEvent) {
        super.touchesBegan(touches, with: event)
        if let touch = touches.first {
            handleTouch(touch)
        }
    }

    override func touchesMoved(_ touches: Set<UITouch>, with event: UIEvent) {
        super.touchesMoved(touches, with: event)
        if let touch = touches.first {
            handleTouch(touch)
        }
    }

    override func touchesEnded(_ touches: Set<UITouch>, with event: UIEvent) {
        super.touchesEnded(touches, with: event)
        state = UIGestureRecognizer.State.failed
    }

    override func touchesCancelled(_ touches: Set<UITouch>, with event: UIEvent) {
        super.touchesCancelled(touches, with: event)
        state = UIGestureRecognizer.State.failed
    }

    private func handleTouch(_ touch: UITouch) {
        guard touch.force != 0 && touch.maximumPossibleForce != 0 else { return }

        if touch.force / touch.maximumPossibleForce >= threshold {
            state = UIGestureRecognizer.State.recognized
        }
    }

}

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Sources:

• GitHub / FlexMonkey - DeepPressGestureRecognizer

• GitHub / ashleymills - ForceTouchGestureRecognizer

• Apple Developer Documentation - Implementing a Discrete Gesture Recognizer