How to track multiple touches

Question

Hey I have a Good peice of code in my touches moved it was given to me by @Sam_M.

Im trying to basically keep track of the location of multiple fingers when there moving. Like Finger 1 is here and Finger 2 in there. So as of right now it will print the number of fingers/touches that are currently on the view and the location but It won't keep track of both individual fingers separately. Ive looked around at the only 3 other question that are on stackoverflow. But none gave me a good result i can implement in swift.

override func touchesBegan(touches: Set<UITouch>, withEvent event: UIEvent?) {

for touch: UITouch in event!.allTouches()! {

for (index,touch) in touches.enumerate() {
    let ptTouch = touch.locationInNode(self.view)
    print("Finger \(index+1): x=\(pTouch.x) , y=\(pTouch.y)")
 }
}

}

override func touchesMoved(touches: Set<UITouch>, withEvent event: UIEvent?) {

for touch: UITouch in event!.allTouches()! {

for (index,touch) in touches.enumerate() {
    let ptTouch = touch.locationInNode(self.view)
    print("Finger \(index+1): x=\(pTouch.x) , y=\(pTouch.y)")
  }
 }
}

Answer 1

The touch object for each finger will stay the same with the same memory address while it's on the screen. You can keep track of individual fingers in a multi touch scenario by storing the address of touch objects in an array and then comparing against that array to know exactly which finger is moving.

var fingers = [String?](count:5, repeatedValue: nil)

override func touchesBegan(touches: Set<UITouch>, withEvent event: UIEvent?) {
    super.touchesBegan(touches, withEvent: event)
    for touch in touches{
        let point = touch.locationInView(self.view)
        for (index,finger)  in fingers.enumerate() {
            if finger == nil {
                fingers[index] = String(format: "%p", touch)
                print("finger \(index+1): x=\(point.x) , y=\(point.y)")
                break
            }
        }            
    }        
}

override func touchesMoved(touches: Set<UITouch>, withEvent event: UIEvent?) {
    super.touchesMoved(touches, withEvent: event)
    for touch in touches {
        let point = touch.locationInView(self.view)
        for (index,finger) in fingers.enumerate() {
            if let finger = finger where finger == String(format: "%p", touch) {
                print("finger \(index+1): x=\(point.x) , y=\(point.y)")
                break
            }
        }
    }
}

override func touchesEnded(touches: Set<UITouch>, withEvent event: UIEvent?) {
    super.touchesEnded(touches, withEvent: event)
    for touch in touches {
        for (index,finger) in fingers.enumerate() {
            if let finger = finger where finger == String(format: "%p", touch) {
                fingers[index] = nil
                break
            }
        }
    }        
}

override func touchesCancelled(touches: Set<UITouch>?, withEvent event: UIEvent?) {
    super.touchesCancelled(touches, withEvent: event)
    guard let touches = touches else {
        return
    }
    touchesEnded(touches, withEvent: event)
}

---

Updated for swift 4

Credit to @Klowne

var fingers = [UITouch?](repeating: nil, count:5)

override func touchesBegan(_ touches: Set<UITouch>, with event: UIEvent?) {
    super.touchesBegan(touches, with: event)
    for touch in touches{
        let point = touch.location(in: self.view)
        for (index,finger)  in fingers.enumerated() {
            if finger == nil {
                fingers[index] = touch
                print("finger \(index+1): x=\(point.x) , y=\(point.y)")
                break
            }
        }
    }
}

override func touchesMoved(_ touches: Set<UITouch>, with event: UIEvent?) {
    super.touchesMoved(touches, with: event)
    for touch in touches {
        let point = touch.location(in: self.view)
        for (index,finger) in fingers.enumerated() {
            if let finger = finger, finger == touch {
                print("finger \(index+1): x=\(point.x) , y=\(point.y)")
                break
            }
        }
    }
}

override func touchesEnded(_ touches: Set<UITouch>, with event: UIEvent?) {
    super.touchesEnded(touches, with: event)
    for touch in touches {
        for (index,finger) in fingers.enumerated() {
            if let finger = finger, finger == touch {
                fingers[index] = nil
                break
            }
        }
    }
}

override func touchesCancelled(_ touches: Set<UITouch>, with event: UIEvent?) {
    super.touchesCancelled(touches, with: event)
    guard let touches = touches else {
        return
    }
    touchesEnded(touches, with: event)
}

*As per apple's updated documentation it's now OK to retain touches during a multi touch sequence as long as they are released at the end of the sequence

Answer 2

A touch is a finger. A finger is a touch. You can identify a finger by identifying the touch; the touch for a particular finger will be identically the same object as long as that finger is touching the screen. To get a unique identifier for a particular UITouch, take its memory address, like this:

let uuid = String(format: "%p", theTouch)

You can store the unique identifier for each touch in a property. But do not store the touch itself; Apple forbids it.