Various NGUI and its EventTrigger usage on script side.

NGUI-EventTrigger

// with tweening animation...
TweenAlpha transition = TweenAlpha.Begin(FadeOut.gameObject, this.fadeInTime, duration);
transition.from = 0f;
transition.ResetToBeginning();
EventDelegate.Add(transition.onFinished, OnFinished, true);

void OnFinished()
{
    // called at the end of alpha tweening animation.
}

// A simple dragging.
// add or retrieve UIEventTrigger
UIEventTrigger eventTrigger = gameObject.GetComponent<UIEventTrigger>();
eventTrigger.onDragEnd.Add(new EventDelegate(OnDragEnd));

...

void OnDragEnd()
{
    // get delta distances with the dragging.
    float delta = UICamera.currentTouch.totalDelta.x;

    // ignore the dragging less than 10
    if (Mathf.Abs(delta) < 10f)
        return;   
        
    // do something 
    // ...
}