需要注意的有下面几点：
1.
区分好表现上的index和逻辑上的index。表现上的index是指这个go是go列表中的第几项，但实际上这个index的意义并不大，因为在滚动的过程中go列表是轮转的；逻辑上的index是指这个go对应数据中的第几项，在滑动的过程中不断地更新逻辑上的index，然后取对应的数据去刷新显示即可。在一般的滑动列表中，有几项数据就生成几个go，因此表现上的index和逻辑上的index是一致的；而在循环利用的循环列表中，这两个是不一致的。
那么，在实现上，就是需要知道每个go对应的逻辑index是多少了。而这个可以简化为，只需要知道第一个对应的逻辑index是多少，因为后面的就是依次递增的。
2.
做好缓存策略。对于循环利用的列表，需要生成的个数等于能显示的最大个数加上2-3个的缓存个数，防止滑动过快时出现穿帮。
3.
关于循环利用的实现。其实就是在滑动过程中，收集被移除显示的go，然后对这些go重新调整位置，并刷新go上的控件显示。那么如何收集呢，就是将go对应的逻辑index和当前的逻辑index范围进行比较，将不在这个范围内的go收集即可。然后在需要的时候取出来，刷新这些go即可。
代码如下：
using UnityEngine;
using System.Collections.Generic;
using System;
using UnityEngine.UI; [RequireComponent(typeof(ScrollRect))]
public class LoopScrollView : MonoBehaviour { private List<GameObject> goList;//当前显示的go列表
private Queue<GameObject> freeGoQueue;//空闲的go队列，存放未显示的go
private Dictionary<GameObject, int> goIndexDic;//key:所有的go value:真实索引
private ScrollRect scrollRect;
private RectTransform contentRectTra;
private Vector2 scrollRectSize;
private Vector2 cellSize;
private int startIndex;//起始索引
private int maxCount;//创建的最大数量
private int createCount;//当前显示的数量 private const int cacheCount = ;//缓存数目
private const int invalidStartIndex = -;//非法的起始索引 private int dataCount;
private GameObject prefabGo;
private Action<GameObject, int> updateCellCB;
private float cellPadding; //初始化SV并刷新
public void Show(int dataCount, GameObject prefabGo, Action<GameObject, int> updateCellCB, float cellPadding = 0f)
{
//数据和组件初始化
this.dataCount = dataCount;
this.prefabGo = prefabGo;
this.updateCellCB = updateCellCB;
this.cellPadding = cellPadding; goList = new List<GameObject>();
freeGoQueue = new Queue<GameObject>();
goIndexDic = new Dictionary<GameObject, int>();
scrollRect = GetComponent<ScrollRect>();
contentRectTra = scrollRect.content;
scrollRectSize = scrollRect.GetComponent<RectTransform>().sizeDelta;
cellSize = prefabGo.GetComponent<RectTransform>().sizeDelta;
startIndex = ;
maxCount = GetMaxCount();
createCount = ; if (scrollRect.horizontal)
{
contentRectTra.anchorMin = new Vector2(, );
contentRectTra.anchorMax = new Vector2(, );
}
else
{
contentRectTra.anchorMin = new Vector2(, );
contentRectTra.anchorMax = new Vector2(, );
}
scrollRect.onValueChanged.RemoveAllListeners();
scrollRect.onValueChanged.AddListener(OnValueChanged);
ResetSize(dataCount);
} //重置数量
public void ResetSize(int dataCount)
{
this.dataCount = dataCount;
contentRectTra.sizeDelta = GetContentSize(); //回收显示的go
for (int i = goList.Count - ; i >= ; i--)
{
GameObject go = goList[i];
RecoverItem(go);
} //创建或显示需要的go
createCount = Mathf.Min(dataCount, maxCount);
for (int i = ; i < createCount; i++)
{
CreateItem(i);
} //刷新数据
startIndex = -;
contentRectTra.anchoredPosition = Vector3.zero;
OnValueChanged(Vector2.zero);
} //更新当前显示的列表
public void UpdateList()
{
for (int i = ; i < goList.Count; i++)
{
GameObject go = goList[i];
int index = goIndexDic[go];
updateCellCB(go, index);
}
} //创建或显示一个item
private void CreateItem(int index)
{
GameObject go;
if (freeGoQueue.Count > )//使用原来的
{
go = freeGoQueue.Dequeue();
goIndexDic[go] = index;
go.SetActive(true);
}
else//创建新的
{
go = Instantiate<GameObject>(prefabGo);
goIndexDic.Add(go, index);
go.transform.SetParent(contentRectTra.transform); RectTransform rect = go.GetComponent<RectTransform>();
rect.pivot = new Vector2(, );
rect.anchorMin = new Vector2(, );
rect.anchorMax = new Vector2(, );
}
goList.Add(go);
go.transform.localPosition = GetPosition(index);
updateCellCB(go, index);
} //回收一个item
private void RecoverItem(GameObject go)
{
go.SetActive(false);
goList.Remove(go);
freeGoQueue.Enqueue(go);
goIndexDic[go] = invalidStartIndex;
} //滑动回调
private void OnValueChanged(Vector2 vec)
{
int curStartIndex = GetStartIndex();
//Debug.LogWarning(curStartIndex); if ((startIndex != curStartIndex) && (curStartIndex > invalidStartIndex))
{
startIndex = curStartIndex; //收集被移出去的go
//索引的范围:[startIndex, startIndex + createCount - 1]
for (int i = goList.Count - ; i >= ; i--)
{
GameObject go = goList[i];
int index = goIndexDic[go];
if (index < startIndex || index > (startIndex + createCount - ))
{
RecoverItem(go);
}
} //对移除出的go进行重新排列
for (int i = startIndex; i < startIndex + createCount; i++)
{
if (i >= dataCount)
{
break;
} bool isExist = false;
for (int j = ; j < goList.Count; j++)
{
GameObject go = goList[j];
int index = goIndexDic[go];
if (index == i)
{
isExist = true;
break;
}
}
if (isExist)
{
continue;
} CreateItem(i);
}
}
} //获取需要创建的最大prefab数目
private int GetMaxCount()
{
if (scrollRect.horizontal)
{
return Mathf.CeilToInt(scrollRectSize.x / (cellSize.x + cellPadding)) + cacheCount;
}
else
{
return Mathf.CeilToInt(scrollRectSize.y / (cellSize.y + cellPadding)) + cacheCount;
}
} //获取起始索引
private int GetStartIndex()
{
if (scrollRect.horizontal)
{
return Mathf.FloorToInt(-contentRectTra.anchoredPosition.x / (cellSize.x + cellPadding));
}
else
{
return Mathf.FloorToInt(contentRectTra.anchoredPosition.y / (cellSize.y + cellPadding));
}
} //获取索引所在位置
private Vector3 GetPosition(int index)
{
if (scrollRect.horizontal)
{
return new Vector3(index * (cellSize.x + cellPadding), , );
}
else
{
return new Vector3(, index * -(cellSize.y + cellPadding), );
}
} //获取内容长宽
private Vector2 GetContentSize()
{
if (scrollRect.horizontal)
{
return new Vector2(cellSize.x * dataCount + cellPadding * (dataCount - ), contentRectTra.sizeDelta.y);
}
else
{
return new Vector2(contentRectTra.sizeDelta.x, cellSize.y * dataCount + cellPadding * (dataCount - ));
}
}
}
using UnityEngine;
using System.Collections;
using UnityEngine.UI; public class TestLoopScrollView : MonoBehaviour { public LoopScrollView loopScrollView;
public LoopScrollView loopScrollView2;
public GameObject prefabGo;
public GameObject prefabGo2; private void Start ()
{ } private void Update()
{
if (Input.GetKeyDown(KeyCode.Q))
{
loopScrollView.Show(, prefabGo, UpdateSV);
}
else if(Input.GetKeyDown(KeyCode.W))
{
loopScrollView.ResetSize();
}
else if (Input.GetKeyDown(KeyCode.E))
{
loopScrollView.ResetSize();
}
else if (Input.GetKeyDown(KeyCode.R))
{
loopScrollView.UpdateList();
} if (Input.GetKeyDown(KeyCode.A))
{
loopScrollView2.Show(, prefabGo2, UpdateSV);
}
else if (Input.GetKeyDown(KeyCode.S))
{
loopScrollView2.ResetSize();
}
else if (Input.GetKeyDown(KeyCode.D))
{
loopScrollView2.ResetSize();
}
else if (Input.GetKeyDown(KeyCode.F))
{
loopScrollView.UpdateList();
}
} private void UpdateSV(GameObject go, int index)
{
Text text = go.transform.Find("Text").GetComponent<Text>();
text.text = index.ToString();
}
}
效果：