unity 注册事件回调

// configure the 2DTK listener eventsvoid OnEnable() {item = GetComponent<tk2dUIItem>();    item.OnDown += downPressed;    item.OnRelease += released;}// remove the 2DTK listener eventsvoid OnDisable() {    item.OnDown -= downPressed;    item.OnRelease -= released;}// initiate the drag sequence from a given positionvoid downPressed () {isBeingDragged = true;startTouch = Input.mousePosition; // save the start position as a reference}// key released... disable the checkvoid released() {isBeingDragged = false;}

   public event System.Action OnDown;

item.OnDown += downPressed;

注册回调函数，当按下时就会回调！