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

The way I am doing this is to use a combination of a UITapGestureRecognizer (provided by Apple) and a DFContinuousForceTouchGestureRecognizer (provided by me).

The DFContinuousForceTouchGestureRecognizer is nice because it provides continuous updates about the pressure changes so you can do things like augment the view as the user varies their pressure on it, as opposed to a single event. If you just want a single event you can ignore eveything in the DFContinuousForceTouchDelegate except the - (void) forceTouchRecognized callback.

https://github.com/foggzilla/DFContinuousForceTouchGestureRecognizer

You can download this and run the sample app on a device that supports force press to see how it feels.

In your UIViewController implement the following:

- (void)viewDidLoad {
    [super viewDidLoad];
    _forceTouchRecognizer = [[DFContinuousForceTouchGestureRecognizer alloc] init];
    _forceTouchRecognizer.forceTouchDelegate = self;

    //here to demonstrate how this works alonside a tap gesture recognizer
    _tapGestureRecognizer = [[UITapGestureRecognizer alloc] initWithTarget:self action:@selector(tapped:)];

    [self.imageView addGestureRecognizer:_tapGestureRecognizer];
    [self.imageView addGestureRecognizer:_forceTouchRecognizer];
}

implement selector for tap gesture

#pragma UITapGestureRecognizer selector

- (void)tapped:(id)sender {
    dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(0.1f * NSEC_PER_SEC)), dispatch_get_main_queue(), ^{
        [[[UIAlertView alloc] initWithTitle:@"Tap" message:@"YEAH!!" delegate:nil cancelButtonTitle:@"OK" otherButtonTitles:nil] show];
    });
}

Implement the delegate protocol for force touch:

#pragma DFContinuousForceTouchDelegate

- (void)forceTouchRecognized:(DFContinuousForceTouchGestureRecognizer *)recognizer {
    self.imageView.transform = CGAffineTransformIdentity;
    [self.imageView setNeedsDisplay];
    dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(0.1f * NSEC_PER_SEC)), dispatch_get_main_queue(), ^{
        [[[UIAlertView alloc] initWithTitle:@"Force Touch" message:@"YEAH!!" delegate:nil cancelButtonTitle:@"OK" otherButtonTitles:nil] show];
    });
}

- (void)forceTouchRecognizer:(DFContinuousForceTouchGestureRecognizer *)recognizer didStartWithForce:(CGFloat)force maxForce:(CGFloat)maxForce {
    CGFloat transformDelta = 1.0f + ((force/maxForce) / 3.0f);
    self.imageView.transform = CGAffineTransformMakeScale(transformDelta, transformDelta);
    [self.imageView setNeedsDisplay];
}

- (void) forceTouchRecognizer:(DFContinuousForceTouchGestureRecognizer *)recognizer didMoveWithForce:(CGFloat)force maxForce:(CGFloat)maxForce {
    CGFloat transformDelta = 1.0f + ((force/maxForce) / 3.0f);
    self.imageView.transform = CGAffineTransformMakeScale(transformDelta, transformDelta);
    [self.imageView setNeedsDisplay];
}

- (void)forceTouchRecognizer:(DFContinuousForceTouchGestureRecognizer *)recognizer didCancelWithForce:(CGFloat)force maxForce:(CGFloat)maxForce  {
    self.imageView.transform = CGAffineTransformIdentity;
    [self.imageView setNeedsDisplay];
}

- (void)forceTouchRecognizer:(DFContinuousForceTouchGestureRecognizer *)recognizer didEndWithForce:(CGFloat)force maxForce:(CGFloat)maxForce  {
    self.imageView.transform = CGAffineTransformIdentity;
    [self.imageView setNeedsDisplay];
}

- (void)forceTouchDidTimeout:(DFContinuousForceTouchGestureRecognizer *)recognizer {
    self.imageView.transform = CGAffineTransformIdentity;
    [self.imageView setNeedsDisplay];
}

Note that this will only be useful on a device that supports force touch.

Also you should not add the DFContinuousForceTouchGestureRecognizer to a view if are you running on iOS 8 or under since it uses the new force property on UITouch only available in iOS 9.

If you add this on iOS 8 it will crash, so conditionally add this recognizer based on what iOS version you are running on if you are supporting versions older than iOS 9.

Answer 2

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
        }
    }

}

---

Sources:

• GitHub / FlexMonkey - DeepPressGestureRecognizer

• GitHub / ashleymills - ForceTouchGestureRecognizer

• Apple Developer Documentation - Implementing a Discrete Gesture Recognizer

Answer 3

I created a UIGestureRecognizer that emulates the behavior of the Apple Mail app. Upon 3D touch, it starts with a short single pulse vibrate and then an optional secondary action (hardTarget) and pulse called by hard pressing shortly after the initial press.

Adapted from https://github.com/FlexMonkey/DeepPressGestureRecognizer

Changes:

• 3D touch vibrate pulses like iOS system behavior
• touch must come up for it to end, like Apple mail app
• threshold defaults to system default level
• hard touch triggers hardAction call like mail app

Note: I added the undocumented system sound k_PeakSoundID, but feel free to turn that off if you are uncomfortable using a constant beyond the documented range. I have been using system sounds with undisclosed constants for years, but you are welcomed to turn off the vibration pulses using the vibrateOnDeepPress property.

import UIKit
import UIKit.UIGestureRecognizerSubclass
import AudioToolbox

class DeepPressGestureRecognizer: UIGestureRecognizer {
    var vibrateOnDeepPress = true
    var threshold: CGFloat = 0.75
    var hardTriggerMinTime: TimeInterval = 0.5

    var onDeepPress: (() -> Void)?

    private var deepPressed: Bool = false {
        didSet {
            if (deepPressed && deepPressed != oldValue) {
                onDeepPress?()
            }
        }
    }

    private var deepPressedAt: TimeInterval = 0
    private var k_PeakSoundID: UInt32 = 1519
    private var hardAction: Selector?
    private var target: AnyObject?

    required init(target: AnyObject?, action: Selector, hardAction: Selector? = nil, threshold: CGFloat = 0.75) {
        self.target = target
        self.hardAction = hardAction
        self.threshold = threshold

        super.init(target: target, action: action)
    }

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

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

    override func touchesEnded(_ touches: Set<UITouch>, with event: UIEvent) {
        super.touchesEnded(touches, with: event)
        state = deepPressed ? UIGestureRecognizerState.ended : UIGestureRecognizerState.failed
        deepPressed = false
    }

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

        let forcePercentage = (touch.force / touch.maximumPossibleForce)
        let currentTime = Date.timeIntervalSinceReferenceDate

        if !deepPressed && forcePercentage >= threshold {
            state = UIGestureRecognizerState.began

            if vibrateOnDeepPress {
                AudioServicesPlaySystemSound(k_PeakSoundID)
            }

            deepPressedAt = Date.timeIntervalSinceReferenceDate
            deepPressed = true

        } else if deepPressed && forcePercentage <= 0 {
            endGesture()

        } else if deepPressed && currentTime - deepPressedAt > hardTriggerMinTime && forcePercentage == 1.0 {
            endGesture()

            if vibrateOnDeepPress {
                AudioServicesPlaySystemSound(k_PeakSoundID)
            }

            //fire hard press
            if let hardAction = self.hardAction, let target = self.target {
                _ = target.perform(hardAction, with: self)
            }
        }
    }

    func endGesture() {
        state = UIGestureRecognizerState.ended
        deepPressed = false
    }
}

// MARK: DeepPressable protocol extension
protocol DeepPressable {
    var gestureRecognizers: [UIGestureRecognizer]? {get set}

    func addGestureRecognizer(gestureRecognizer: UIGestureRecognizer)
    func removeGestureRecognizer(gestureRecognizer: UIGestureRecognizer)

    func setDeepPressAction(target: AnyObject, action: Selector)
    func removeDeepPressAction()
}

extension DeepPressable {

    func setDeepPressAction(target: AnyObject, action: Selector) {
        let deepPressGestureRecognizer = DeepPressGestureRecognizer(target: target, action: action, threshold: 0.75)
        self.addGestureRecognizer(gestureRecognizer: deepPressGestureRecognizer)
    }

    func removeDeepPressAction() {
        guard let gestureRecognizers = gestureRecognizers else { return }

        for recogniser in gestureRecognizers where recogniser is DeepPressGestureRecognizer {
            removeGestureRecognizer(gestureRecognizer: recogniser)
        }
    }
}

Answer 4

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 5

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).