Unity UGUI Scroll View（滾動列表）優化
在遊戲中很多UI設計都需要用到 Scroll View 控制元件，如排行榜、聊天室、揹包等。當需要顯示的物品達到千量級以上的時候，就會造成大量記憶體上的佔用，列表滾動的時候也會觸發大量的計算，會照成卡頓。接下來講講如何對其優化。

注意看Hierarchy中UIgrid下始終只有4個Item
優化策略就是隻建立螢幕能放下的item的數量再加一個的item。當列表滾動時利用再外面不顯示出來的item進行設定座標即可。
方法還是不難的，所以我們直接看程式碼，註釋只寫出了grid上移時的情況，其餘同理。

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

public class ScrollViewManager : MonoBehaviour
{
    public enum style {
        Horizontal,                         //橫向分佈
        Vertical,                           //縱向分佈
 

        //HorizontalAndVertical               //橫向和縱向分佈
    };

    public Image scrollView;                //scroll view  
    public Image grid;                      //grid
    public Scrollbar HorizontalScrollBar;   //控制horizontal的scroll bar
    public Scrollbar VerticalScrollBar;     //控制vertical的scroll bar
 

    public int number;                      //物品總數量
    public float middle;                    //物品間距
    public style manage_style;              //管理物品方式
    //public int rowCount;                    //行數
    //public int columnCount;                 //列數
    public string prefab_path;              //物品資源路徑

    private List<Item> itemList;            //存放物品的列表
    private float item_width;               //物品寬度
    private float item_height;              //物品高度
    private float sv_width;                 //scroll view寬度
    private float sv_height;                //scroll view高度   
    private float grid_width;               //grid寬度
    private float grid_height;              //grid高度
    private int row;                        //grid內可放物品行數
    private int column;                     //grid內可放物品列數
    private GameObject gameObj;             //物品物件
    private GameObject obj;                 //例項化物品物件
    private Vector3 gridOldPosition;        //grid更新前的座標

    // Use this for initialization
    void Start()
    {
        gameObj = Resources.Load(prefab_path) as GameObject;   \\載入prefab
        grid.transform.localPosition = new Vector3(0, 0, 0);   \\設定grid座標
        item_width = gameObj.transform.GetComponent<RectTransform>().rect.size.x;  \\獲取Item寬高
        item_height = gameObj.transform.GetComponent<RectTransform>().rect.height;
        sv_width = scrollView.transform.GetComponent<RectTransform>().rect.size.x;  \\獲取scroll view 寬高
        sv_height = scrollView.transform.GetComponent<RectTransform>().rect.height;
        HorizontalScrollBar.transform.GetComponent<RectTransform>().sizeDelta = new Vector2(sv_width ,30);    //設定scroll bar座標
        HorizontalScrollBar.transform.localPosition = new Vector3(0, -sv_height, 0) + scrollView.transform.localPosition;
        VerticalScrollBar.transform.GetComponent<RectTransform>().sizeDelta = new Vector2(30, sv_height);
        VerticalScrollBar.transform.localPosition = new Vector3(sv_width, 0, 0) + scrollView.transform.localPosition;
        itemList = new List<Item>();

        switch (manage_style)  //根據所選排列方式初始化建立Item
        {
            case style.Horizontal:
                grid_width = number * (middle + item_width);
                column = GetUpInt(sv_width, item_width + middle) + 1;
                if (grid_width <= sv_width)
                {
                    column = number;
                    grid_width = sv_width;
                }
                grid_height = sv_height;
                row = 1;
                grid.transform.GetComponent<RectTransform>().sizeDelta = new Vector2(grid_width, grid_height);   
                HorizontalInitItem();
                break;

            case style.Vertical:
                grid_width = sv_width;
                column = 1;
                grid_height = number * (middle + item_height);
                row = GetUpInt(sv_height, item_height + middle) + 1;
                if (grid_height <= sv_height)
                {
                    row = number;
                    grid_height = sv_height;
                }
                grid.transform.GetComponent<RectTransform>().sizeDelta = new Vector2(grid_width, grid_height);
                VerticalInitItem();
                break;

            //case style.HorizontalAndVertical:   //既上下滑動又左右滑動的有些問題先註釋掉
            //    grid_width = columnCount * (middle + item_width);
            //    column = (int)(sv_width / (item_width + middle)) + 1;
            //    if (grid_width <= sv_width)
            //    {
            //        column = columnCount;
            //        grid_width = sv_width;                   
            //    }
            //    grid_height = rowCount * (middle + item_height);
            //    row = (int)(sv_height / (item_height + middle)) + 1;
            //    if (grid_height <= sv_height)
            //    {
            //        row = rowCount;
            //        grid_height = sv_height;
            //    }
            //    grid.transform.GetComponent<RectTransform>().sizeDelta = new Vector2(grid_width, grid_height);
            //    HorizontalAndVerticalInitItem();
            //    break;
        }

    }

    void HorizontalInitItem() {

        for (int i = 0; i < column; i++) {
            obj = Instantiate(gameObj);
            obj.transform.SetParent(grid.transform);
            obj.transform.localPosition = new Vector3(middle / 2 + item_width / 2 + (middle + item_width) * i, -(sv_height / 2), 0);
            Item item = new Item();
            item.BindGameObject(obj);
            item.SetData(i + 1);
            itemList.Add(item);
        }

    }

    void VerticalInitItem() {

        for (int i = 0; i < row; i++){
            obj = Instantiate(gameObj);
            obj.transform.SetParent(grid.transform);
            obj.transform.localPosition = new Vector3(sv_width / 2, -(middle / 2 + item_height / 2 + (middle + item_height) * i), 0);
            Item item = new Item();
            item.BindGameObject(obj);
            item.SetData(i + 1);
            itemList.Add(item);
        }

    }

    //void HorizontalAndVerticalInitItem() {

    //    for (int i = 0; i < row; i++) {
    //        for (int j = 0; j < column; j++) {
    //            obj = Instantiate(gameObj);
    //            obj.transform.SetParent(grid.transform);
    //            obj.transform.localPosition = new Vector3(middle / 2 + item_width / 2 + (middle + item_width) * j, -(middle / 2 + item_height / 2 + (middle + item_height) * i), 0);
    //            Item item = new Item();
    //            item.BindGameObject(obj);
    //            item.SetData(i * columnCount + j + 1);
    //            itemList.Add(item);
    //        }
    //    }
    //}

    // Update is called once per frame
    //根據grid的移動調整Item的位置
    void Update()
    {

        Vector3 gridNewPosition = grid.transform.localPosition;

        float h = gridNewPosition.y - gridOldPosition.y;

        float w = gridNewPosition.x - gridOldPosition.x;

        gridOldPosition = grid.transform.localPosition;

        if (h > 0.05f)
        {   \\當最後一個Item的值小於總量
            if (itemList[row - 1].GetData() < number)
            {   \\當第一個Item的位置已經超出了一gird上一個Item的距離
                while (itemList[0].GetGameObjectPosition().y + gridNewPosition.y > (item_height + middle) / 2)
                {
                    Up();    //調整第一個Item位置
                }
            }
        }
        else if (h < -0.05f)
        {
            if (itemList[0].GetData() > 1)
            {
                while (itemList[row - 1].GetGameObjectPosition().y + gridNewPosition.y < -(sv_height + (item_height + middle) / 2))
                {
                    Down();
                }
            }
        }
        if (w > 0.05f)
        {
            if (itemList[0].GetData() > 1)
            {
                while (itemList[column - 1].GetGameObjectPosition().x + gridNewPosition.x > (sv_width + (item_width + middle) / 2))
                {
                    Right();
                }
            }
        }
        else if (w < -0.05f)
        {
            if (itemList[column - 1].GetData() < number)
            {
                while (itemList[0].GetGameObjectPosition().x + gridNewPosition.x < -((item_width + middle) / 2))
                {
                    Left();
                }
            }
        }

    }

    void Up(){
            //將第一個Item的位置放到最後一個Itemd的下方
        itemList[0].SetGameObjectPosition(itemList[row - 1].GetGameObjectPosition() + new Vector3(0, -(item_height + middle), 0));
        itemList[0].SetData(itemList[row - 1].GetData() + 1);
        itemList.Add(itemList[0]);
        itemList.RemoveAt(0);

    }

    void Down() {

        itemList[row - 1].SetGameObjectPosition(itemList[0].GetGameObjectPosition() + new Vector3(0, item_height + middle, 0));
        itemList[row - 1].SetData(itemList[0].GetData() - 1);
        itemList.Insert(0, itemList[row - 1]);
        itemList.RemoveAt(row);

    }

    void Left(){

        itemList[0].SetGameObjectPosition(itemList[column - 1].GetGameObjectPosition() + new Vector3(item_width + middle, 0, 0));
        itemList[0].SetData(itemList[column - 1].GetData() + 1);
        itemList.Add(itemList[0]);
        itemList.RemoveAt(0);

    }

    void Right() {

        itemList[column - 1].SetGameObjectPosition(itemList[0].GetGameObjectPosition() + new Vector3(-(item_width + middle), 0, 0));
        itemList[column - 1].SetData(itemList[0].GetData() - 1);
        itemList.Insert(0, itemList[column - 1]);
        itemList.RemoveAt(column);

    }

    int GetUpInt(float a, float b) {

        int i = 0;

        while (a > 0) {
            a -= b;
            i++;
        }

        return i;
    } 
}