UGUI 下拉滚动框

using UnityEngine;
using System.Collections;
using UnityEngine.UI;
using UnityEngine.EventSystems;
using System.Collections.Generic;
using UnityEngine.Events;

public class DropScroll : MonoBehaviour {

[SerializeField]
private Button[] btnList;               //提供多个按钮
private RectTransform thisRT;

[SerializeField]
private GameObject scrollViewTmp;       //提供一个滚动视图模版
private List<RectTransform> scrollViewList = new List<RectTransform>();

public void Start()
{
Init();
}

public void Init()
{
RectTransform rt = null;

foreach (var btn in btnList)
{
EventTriggerListener.Get(btn.gameObject).OnClick += BtnDropClickEvent;
rt = GameObject.Instantiate(scrollViewTmp).GetComponent<RectTransform>();
scrollViewList.Add(rt);
rt.gameObject.SetActive(false);
rt.transform.SetParent(this.transform,false);
}

thisRT = this.GetComponent<RectTransform>();
}

private void BtnDropClickEvent(GameObject go)
{
RectTransform rt = go.GetComponent<RectTransform>();
RectTransform btnRt = null;
float height = thisRT.sizeDelta.y;
int index = rt.GetSiblingIndex();

HideAllScrollView();
scrollViewList[index].sizeDelta = new Vector2(thisRT.sizeDelta.x, height - btnList.Length * rt.sizeDelta.y);
scrollViewList[index].anchoredPosition = new Vector2(0, -((index + 1) * rt.sizeDelta.y));
scrollViewList[index].gameObject.SetActive(true);

for (int i = 0; i < btnList.Length; i++)
{
btnRt = btnList[i].GetComponent<RectTransform>();
if (i > index)
{
btnRt.anchoredPosition = new Vector2(btnRt.anchoredPosition.x, -height + ((btnList.Length - i) * btnRt.sizeDelta.y));
}
else
{
btnRt.anchoredPosition = new Vector2(btnRt.anchoredPosition.x, -(i * btnRt.sizeDelta.y));
}
}
}

private void HideAllScrollView()
{
for (int i = 0; i < scrollViewList.Count; i++)
{
scrollViewList[i].gameObject.SetActive(false);
}
}
}

public class EventTriggerListener : UnityEngine.EventSystems.EventTrigger
{
public delegate void VoidDelegate(GameObject go);
public event VoidDelegate OnClick;

static public EventTriggerListener Get(GameObject go)
{
EventTriggerListener listener = go.GetComponent<EventTriggerListener>();

if (listener == null)
listener = go.AddComponent<EventTriggerListener>();

return listener;
}

public override void OnPointerClick(PointerEventData eventData)
{
if (OnClick != null)
OnClick(gameObject);
}
}