Two finger swipe

Notes on implementing two finger swipe for macOS


In your NSView:

var twoFingersTouches:[String:NSTouch]?/*temp storage for the twoFingerTouches data*/

override func touchesBegan(with event:NSEvent) {
    twoFingersTouches = GestureUtils.twoFingersTouches(self, event)
override func touchesMoved(with event:NSEvent) {
    let swipeType:SwipeType = GestureUtils.swipe(self, event, twoFingersTouches)
    if (swipeType == .right){
        Swift.print("swipe right")
    }else if(swipeType == .left){
        Swift.print("swipe left")

The Reusable Utility code:

enum SwipeType{/*Two finger swipe type*/
    case left,right,none
class GestureUtils{
     * To avoid duplicate code we could extract the content of this method into an GestureUtils method. Return nil if there isn't 2 touches and set the array only if != nil
    static func twoFingersTouches(_ view:NSView, _ event:NSEvent)->[String:NSTouch]?{
        var twoFingersTouches:[String:NSTouch]? = nil//NSMutualDictionary was used before and didn't require casting id to string, revert if side-effects manifest
        if(event.type == NSEventType.gesture){// could maybe be: EventTypeBeginGesture
            let touches:Set<NSTouch> = event.touches(matching:NSTouchPhase.any, in: view)//touchesMatchingPhase:NSTouchPhaseAny inView:self
            if(touches.count == 2){
                twoFingersTouches = [String:NSTouch]()
                for touch in touches {//
                    //Swift.print("id: "+"\((touch as! NSTouch).identity)")
                    twoFingersTouches!["\((touch).identity)"] = touch/*assigns each touch to the identity of the same touch*///was [ setObject: forKey:];
        return twoFingersTouches
     * Detects 2 finger (left/right) swipe gesture
     * NOTE: either of 3 enums is returned: .leftSwipe, .rightSwipe .none
     * TODO: also make up and down swipe detectors, and do more research into how this could be done easier. Maybe you even have some clues in the notes about gestures etc.
     * Conceptually:
     * 1. Record 2 .began touchEvents
     * 2. Record 2 .ended touchEvents
     * 3. Measure the distance between .began and .ended and assert if it is within threshold
    static func swipe(_ view:NSView, _ event:NSEvent, _ twoFingersTouches:[String:NSTouch]?) -> SwipeType{
        let endingTouches:Set<NSTouch> = event.touches(matching: NSTouchPhase.ended, in: view)
        if(endingTouches.count > 0 && twoFingersTouches != nil){
            let beginningTouches:[String:NSTouch] = twoFingersTouches!/*copy the twoFingerTouches data*/
            var magnitudes:[CGFloat] = []/*magnitude definition: the great size or extent of something.*/
            for endingTouch in endingTouches {
                let beginningTouch:NSTouch? = beginningTouches["\(endingTouch.identity)"]
                if (beginningTouch == nil) {continue}//skip if endingTouch doesn't have a matching beginningTouch
                let magnitude:CGFloat = endingTouch.normalizedPosition.x - beginningTouch!.normalizedPosition.x
            var sum:CGFloat = 0
            for magnitude in magnitudes{
                sum += magnitude
            let absoluteSum:CGFloat = abs(sum)/*force value to be positive*/
            let kSwipeMinimumLength:CGFloat = 0.1
            if (absoluteSum < kSwipeMinimumLength) {return .none}/*Assert if the absolute sum is long enough to be considered a complete gesture*/
            if (sum > 0){
                return .right
            }else /*if(sum < 0)*/{
                return .left
        return .none/*no swipe direction detected*/