Unity UI system PageViewController

PageViewController.cs

using System;
using UnityEngine;
using UnityEngine.EventSystems;

public class PageViewController : MonoBehaviour, IBeginDragHandler, IDragHandler, IEndDragHandler, IInitializePotentialDragHandler
{
    public enum Direction
    {
        Horizontal,
        Vertical
    }

    public Direction direction;

    public RectTransform content;

    public int pageCount;

    public float pageWidth = 100;

    public float elasticity = 0.1f;

    [Range(0.1f, 0.5f), Tooltip("滑动结束判断更改Page的阈值")]
    public float threshold = 0.4f;

    public float velocityThreshold = 30f;

    public int page;

    public float contentOffset;

    float currentVelocity;

    float value;

    float targetValue;

    bool isDrag = false;

    bool isDamping = true;

    public void OnBeginDrag(PointerEventData eventData)
    {
        isDrag = true;
        currentVelocity = 0;
    }

    public void OnDrag(PointerEventData eventData)
    {
        if (direction == Direction.Horizontal)
        {
            value -= eventData.delta.x;
            currentVelocity = -eventData.delta.x / Time.deltaTime;
        }
        else if (direction == Direction.Vertical)
        {
            value += eventData.delta.y;
            currentVelocity = eventData.delta.y / Time.deltaTime;
        }

        UpdateContentPosition();
    }

    public void OnEndDrag(PointerEventData eventData)
    {
        isDrag = false;

        if (direction == Direction.Horizontal)
        {
            currentVelocity = -eventData.delta.x / Time.deltaTime;
        }
        else
        {
            currentVelocity = eventData.delta.y / Time.deltaTime;
        }
        isDamping = true;
        targetValue = CalculateTargetValue();
    }

    void LateUpdate()
    {
        Reposition();
    }

    void Reposition()
    {
        if (!isDrag && isDamping)
        {
            value = Mathf.SmoothDamp(value, targetValue, ref currentVelocity, elasticity);
            if (Mathf.Abs(currentVelocity) < 1)
            {
                currentVelocity = 0;
            }
            if (Mathf.Abs(targetValue - value) < 0.1)
            {
                value = targetValue;
                isDamping = false;
            }

            UpdateContentPosition();
        }
    }

    void UpdateContentPosition()
    {
        Vector2 vector = content.anchoredPosition;
        if (direction == Direction.Horizontal)
        {
            vector.x = contentOffset - value;
        }
        else
        {
            vector.y = value - contentOffset;
        }
        content.anchoredPosition = vector;
    }

    float CalculateTargetValue()
    {
        float pageIndex = value / pageWidth;

        float delta = pageIndex - Mathf.Floor(pageIndex);

        if (Mathf.Abs(currentVelocity) > velocityThreshold)
        {
            if (currentVelocity > 0)
            {
                if (delta > threshold)
                {
                    pageIndex = Mathf.Ceil(pageIndex);
                }
                else
                {
                    pageIndex = Mathf.Floor(pageIndex);
                }
            }
            else
            {
                if (delta > threshold)
                {
                    pageIndex = Mathf.Floor(pageIndex);
                }
                else
                {
                    pageIndex = Mathf.Ceil(pageIndex);
                }
            }
        }
        else
        {
            pageIndex = Mathf.Round(pageIndex);
        }

        if (pageCount > 0)
        {
            pageIndex = Mathf.Clamp(pageIndex, 0, pageCount - 1);
        }
        return pageIndex * pageWidth;
    }

    public void OnInitializePotentialDrag(PointerEventData eventData)
    {
        isDamping = false;
        currentVelocity = 0;
    }
}