FlickHandler.cs

public class FlickHandler : MonoBehaviour, IPointerDownHandler, IPointerUpHandler {

	[System.Serializable]
	public class DetectThreshold {
		public float minDistance;
		public float maxDistance;
		public float deltaTime;
		public float deltaAng;
	}
	public DetectThreshold threshold;

	private struct FlickAction {
		public Vector2       dir;
		public System.Action action;
	}
	private List<FlickAction> flickActions;

	private struct TouchData {
		public Vector2 pos;
		public float   time;

		public TouchData DeltaTo(TouchData to) {
			return new TouchData () {pos = to.pos - pos, time = to.time - time}; 
		}
	}
	private Dictionary<int, TouchData> touchDowns;

	public void Initialize() {
		flickActions = new List<FlickAction> ();
		touchDowns   = new Dictionary<int, TouchData> (); 
	}

	public void AddFlickEvent(Vector2 dir, System.Action action) {
		flickActions.Add(new FlickAction(){ dir = dir.normalized, action = action });
	}

	public void OnPointerDown (PointerEventData eventData) {
		TouchDownEvent (eventData.pointerId, eventData.position);
	}
	
	public void OnPointerUp (PointerEventData eventData)  {
		TouchUpEvent (eventData.pointerId, eventData.position);
	}

	private void TouchDownEvent(int id, Vector2 pos) {
		//Debug.Log ("down: " + pos + ", " + Time.time);
		touchDowns [id] = new TouchData () {pos = pos, time = Time.time}; 
	}

	private void TouchUpEvent(int id, Vector2 pos) {
		//Debug.Log ("up: " + pos + ", " + Time.time);
		if (!touchDowns.ContainsKey (id)) Debug.Log ("god bless you");

		TouchData down  = touchDowns [id];
		TouchData up    = new TouchData () {pos = pos, time = Time.time};  
		TouchData delta = down.DeltaTo (up);
		 
		if (IsValidFlick (delta)) {
			List<System.Action> actions = GetActionsWith(delta.pos);
			actions.ForEach(a => a());
		}

	}

	private bool IsValidFlick(TouchData delta) {
		if (delta.time > threshold.deltaTime)             return false;
		if (delta.pos.magnitude  < threshold.minDistance) return false;
		if (delta.pos.magnitude  > threshold.maxDistance) return false;

		return true;
	}

	private List<System.Action> GetActionsWith(Vector2 dir) {
		Vector2 v = dir.normalized;

		List<System.Action> r =  flickActions
			.Where(a => Vector2.Dot(v, a.dir) > Mathf.Cos(threshold.deltaAng * Mathf.Deg2Rad))
			.Select(a => a.action).ToList();

		return r;
	}

}