实现效果：ScrollRect，格子动态缩放大小，滑动结束自动定位中间格子
使用说明：
目前只支持横向从左往右列表，需要设置ScrollRect仅横向滑动，ScrollViewExtras挂到ScrollRect组件所在节点，ScrollRect的格子锚点、中心点设置在左上角，Content，设置好Y坐标，运行时自动修改X坐标。
GridSpace：格子间距
IsSnap：是否开启自动定位
IsScale：是否开启自动缩放
ScaleCueve：缩放曲线
效果演示：
关闭自动定位，关闭自动缩放：
开启自动定位，关闭自动缩放：
关闭自动定位，开启自动缩放：
开启自动定位，开启自动缩放：
实现原理：
- 动态缩放功能实现：Transform改变时，计算列表可视区域内所有格子与列表中心的偏移量，根据偏移量缩放格子。
- 自动定位功能实现：初始化计算每个格子的位置，滑动结束后，计算每个格子到列表中心的偏移量，偏移量最小的格子就是列表最中间的格子，再把它自动移动到列表中心的位置，实现定位。
实现代码：
using System.Collections;
using System.Collections.Generic;
using UnityEngine;
using UnityEngine.UI;
using UnityEngine.EventSystems;
using System;
[RequireComponent(typeof(ScrollRect))]
public class ScrollViewExtras : MonoBehaviour, IBeginDragHandler, IDragHandler, IEndDragHandler
{
private enum SnapState
{
None,
Inertia,
Reverse,
}
public Action OnScrollStartDrag;
public Action<int> OnScrollEndDrag;
public Action<int> OnSelectGridChanged;
[SerializeField] private float gridSpace = 20;
[SerializeField] private bool isSnap;
[SerializeField] private bool isScale;
[SerializeField] private AnimationCurve scaleCurve = new AnimationCurve(new Keyframe(0,1),new Keyframe(1,0.5f));
//初始化不变字段
private ScrollRect scrollRect;
private RectTransform contentRectTrans;
private Vector2 scrollHalfSize; //列表尺寸
private Vector2 gridSize;
private List<RectTransform> gridList = new List<RectTransform>();
private List<Vector2> gridCenterList = new List<Vector2>();
private float snapDecelerate;
private const float snapReverseSpeed = 500;
private bool isInited = false;
//动态变化字段
private SnapState snapState = SnapState.None;
private int curSelectIndex;
//----------
private void Start()
{
Init();
}
private void Update()
{
if(isInited)
{
switch(snapState)
{
case SnapState.Inertia:
UpdateSnapInertia();
break;
case SnapState.Reverse:
UpdateSnapReverse();
break;
default:
break;
}
if(contentRectTrans.hasChanged)
{
if(isScale)
UpdateScale();
else
UpdateSelectGrid();
}
}
}
#region --- Drag Event
public void OnBeginDrag(PointerEventData eventData)
{
OnScrollStartDrag?.Invoke();
BreakSnap();
}
public void OnDrag(PointerEventData eventData)
{
}
public void OnEndDrag(PointerEventData eventData)
{
StartSnap();
}
#endregion
public void Init()
{
scrollRect = GetComponent<ScrollRect>();
if(!scrollRect.horizontal)
Debug.LogError("目前只支持横向从左往右列表");
contentRectTrans = scrollRect.content;
if(contentRectTrans.pivot.x > 0)
Debug.LogError("目前只支持横向从左往右列表");
//scrollCenter = scrollRect.viewport.rect.center;
scrollHalfSize = scrollRect.viewport.rect.size * 0.5f;
for(int i = 0; i < contentRectTrans.childCount; i++)
{
gridList.Add(contentRectTrans.GetChild(i) as RectTransform);
}
if(gridList.Count > 0)
gridSize = gridList[0].rect.size;
snapDecelerate = scrollRect.decelerationRate;
//if(snapDecelerate < 0.1f)
// snapDecelerate = 0.1f;
if(gridList.Count == 0)
return;
//第一个格子坐标
Vector2 gridInitPos = gridList[0].anchoredPosition;
gridInitPos.x = scrollHalfSize.x - gridSize.x * 0.5f;
//格子间隔
Vector2 gridOffset = Vector2.zero;
gridOffset.x = gridSize.x + gridSpace;
//计算画布尺寸
Vector2 contentSize = contentRectTrans.rect.size;
contentSize.x = gridSize.x * gridList.Count + gridSpace * (gridList.Count - 1) + scrollHalfSize.x * 2 - gridSize.x;
//设置画布尺寸
contentRectTrans.sizeDelta = contentSize;
contentRectTrans.anchoredPosition = new Vector2(0,contentRectTrans.anchoredPosition.y);
//设置每个格子坐标
for(int i = 0; i < gridList.Count; i++)
{
gridList[i].anchoredPosition = gridInitPos + gridOffset * i;
gridList[i].anchorMin = new Vector2(0,1);
gridList[i].anchorMax = new Vector2(0,1);
gridList[i].pivot = new Vector2(0,1);
gridCenterList.Add(gridList[i].anchoredPosition + gridSize * 0.5f);
}
if(isScale)
UpdateScale();
isInited = true;
curSelectIndex = 0;
}
#region --- Snap ---
private Vector2 snapTargetPos;
private void StartSnap()
{
if(isSnap)
{
if(gridList.Count > 0)
{
snapState = SnapState.Inertia;
}
}
}
private void UpdateSnapInertia()
{
if(scrollRect.velocity.x > -snapReverseSpeed && scrollRect.velocity.x < snapReverseSpeed)
{
//反向
StartSnapReverse();
return;
}
}
private void StartSnapReverse()
{
snapState = SnapState.Reverse;
scrollRect.StopMovement();
//当前屏幕中心的画布坐标
float centerPos = Mathf.Abs(contentRectTrans.anchoredPosition.x) + scrollHalfSize.x;
float temOffset;
float minOffet = float.MaxValue;
for(int i = 0; i < gridCenterList.Count; i++)
{
if(!gridList[i].gameObject.activeSelf)
continue;
//格子中心坐标
temOffset = centerPos - gridCenterList[i].x;
//比较最小距离
if(Mathf.Abs(temOffset) < Mathf.Abs(minOffet))
{
minOffet = temOffset;
//格子在中间，反推画布的坐标
snapTargetPos.x = -(gridCenterList[i].x - scrollHalfSize.x);
}
}
snapTargetPos.y = contentRectTrans.anchoredPosition.y;
}
private void UpdateSnapReverse()
{
if(Mathf.Abs(contentRectTrans.anchoredPosition.x - snapTargetPos.x) < 1)
{
contentRectTrans.anchoredPosition = snapTargetPos;
EndSnap();
return;
}
contentRectTrans.anchoredPosition = Vector2.Lerp(contentRectTrans.anchoredPosition,snapTargetPos,snapDecelerate);
}
private void EndSnap()
{
if(snapState == SnapState.None)
return;
scrollRect.StopMovement();
snapState = SnapState.None;
if(isScale)
UpdateScale();
OnScrollEndDrag?.Invoke(curSelectIndex);
}
private void BreakSnap()
{
if(snapState != SnapState.None)
snapState = SnapState.None;
}
#endregion
#region --- Scale ---
int tempIndex;
float tempCenter;
float tempOffset;
float minDistance;
Vector3 tempScale;
Vector2 tempAnPos;
private void UpdateScale()
{
minDistance = float.MaxValue;
tempCenter = Mathf.Abs(contentRectTrans.anchoredPosition.x) + scrollHalfSize.x;
for(int i = 0; i < gridCenterList.Count; i++)
{
if(!gridList[i].gameObject.activeSelf)
continue;
//格子中心到屏幕中心距离
tempOffset = Mathf.Abs(tempCenter - gridCenterList[i].x);
if(tempOffset > scrollHalfSize.x + gridSize.x)
continue;
//计算缩放值
tempScale.x = scaleCurve.Evaluate(tempOffset / scrollHalfSize.x);
tempScale.y = tempScale.x;
tempScale.z = 1;
//修改缩放
gridList[i].localScale = tempScale;
//修改位置（锚点在左上角，保证缩放后格子仍然在中间）
tempAnPos.x = gridCenterList[i].x - gridSize.x * 0.5f * tempScale.x;
tempAnPos.y = gridCenterList[i].y + gridSize.y * (0.5f * tempScale.y - 1);
gridList[i].anchoredPosition = tempAnPos;
//比较最小距离
if(tempOffset < minDistance)
{
minDistance = tempOffset;
tempIndex = i;
}
}
if(curSelectIndex != tempIndex)
{
curSelectIndex = tempIndex;
OnSelectGridChanged?.Invoke(curSelectIndex);
}
}
private void UpdateSelectGrid()
{
minDistance = float.MaxValue;
tempCenter = Mathf.Abs(contentRectTrans.anchoredPosition.x) + scrollHalfSize.x;
for(int i = 0; i < gridCenterList.Count; i++)
{
if(!gridList[i].gameObject.activeSelf)
continue;
//格子中心到屏幕中心距离
tempOffset = Mathf.Abs(tempCenter - gridCenterList[i].x);
if(tempOffset > scrollHalfSize.x + gridSize.x)
continue;
//比较最小距离
if(tempOffset < minDistance)
{
minDistance = tempOffset;
tempIndex = i;
}
}
if(curSelectIndex != tempIndex)
{
curSelectIndex = tempIndex;
OnSelectGridChanged?.Invoke(curSelectIndex);
}
}
#endregion
}