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);

    }

}