UGUI 分页渐变居中效果

代码相当冗长，仅作自己记录

在此分页上修改的https://blog.csdn.net/qinyuanpei/article/details/49781133

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

public class GridItem {
    public string cnName;
    public string usName;

    public GridItem(string cnN,string usN) {
        cnName = cnN;
        usName = usN;
    }
}

public class PaginationPanel : MonoBehaviour
{
    /// <summary>
    /// 当前页面索引
    /// </summary>
    public int m_PageIndex = 1;

    /// <summary>
    /// 总页数
    /// </summary>
    public int m_PageCount = 0;

    /// <summary>
    /// 每页元素数
    /// </summary>
    public int m_PerPageCount = 0;

    /// <summary>
    /// 元素总个数
    /// </summary>
    public int m_ItemsCount = 0;

    /// <summary>
    /// 元素列表
    /// </summary>
    public List<GridItem> m_ItemsList;

    /// <summary>
    /// 上一页
    /// </summary>
    public Button m_BtnPrevious;

    /// <summary>
    /// 下一页
    /// </summary>
    public Button m_BtnNext;

    /// <summary>
    /// 显示当前页数的标签
    /// </summary>
    public Text m_PanelText;

    public Transform m_FrontPanel;
    public Transform m_BackPanel;

    public bool m_IsTouching;
    [Range(-1,1)]
    public float m_TouchDelta;

    public float m_MoveSpeed = 5f;
    public float m_FadeDistance;
    public Vector3 m_PrePos;
    public Vector3 m_CenterPos;
    public Vector3 m_NextPos;

    public bool m_DoPrevious;
    public bool m_DoNext;

    public float m_CurrAlpha;
    private bool m_HasPrevious;
    private bool m_HasNext;
    private bool m_IsSaveBeforeTouch;
    public int m_FrontPanelPageIndex;
    private bool m_CanChangePage;
    private bool m_IsBackPageIndex;
    void Start()
    {
        InitGUI();
        InitItems();
    }

    /// <summary>
    /// 初始化GUI
    /// </summary>
    private void InitGUI()
    {
        //m_BtnNext = GameObject.Find("Canvas/Panel/BtnNext").GetComponent<Button>();
        //m_BtnPrevious = GameObject.Find("Canvas/Panel/BtnPrevious").GetComponent<Button>();
        //m_PanelText = GameObject.Find("Canvas/Panel/Text").GetComponent<Text>();

        //为上一页和下一页添加事件
        m_BtnNext.onClick.AddListener(() => { OnNextBtnClick(); });
        m_BtnPrevious.onClick.AddListener(() => { OnPreviousBtnClick(); });
        m_PerPageCount = m_FrontPanel.childCount;
        m_FadeDistance = Mathf.Abs(m_FrontPanel.localPosition.y - m_BackPanel.localPosition.y);
        m_PrePos = m_FrontPanel.localPosition;
        m_PrePos.y += m_FadeDistance;
        m_NextPos = m_FrontPanel.localPosition;
        m_NextPos.y -= m_FadeDistance;
        m_CenterPos = m_FrontPanel.localPosition;
        m_CanChangePage = true;
        m_FrontPanelPageIndex = 1;
    }

    /// <summary>
    /// 初始化元素
    /// </summary>
    private void InitItems()
    {
        //准备一个存储着12生肖信息的数组
        GridItem[] items = new GridItem[]
        {
            new GridItem("鼠","Mouse"),
            new GridItem("牛","Ox"),
            new GridItem("虎","Tiger"),
            new GridItem("兔","Rabbit"),
            new GridItem("龙","Dragon"),
            new GridItem("蛇","Snake"),
            new GridItem("马","Horse"),
            new GridItem("羊","Goat"),
            new GridItem("猴","Monkey"),
            new GridItem("鸡","Rooster"),
            new GridItem("狗","Dog"),
            new GridItem("猪","Pig")
        };

        //利用12生肖数组来随机生成列表
        m_ItemsList = new List<GridItem>();
        for (int i = 0; i < items.Length; i++)
        {
            m_ItemsList.Add(items[i]);
        }

        //计算元素总个数
        m_ItemsCount = m_ItemsList.Count;
        //计算总页数
        m_PageCount = (m_ItemsCount % m_PerPageCount) == 0 ? m_ItemsCount / m_PerPageCount : (m_ItemsCount / m_PerPageCount) + 1;

        BindPage(m_FrontPanel, m_PageIndex);
        
        //更新界面页数
        m_PanelText.text = string.Format("{0}/{1}", m_PageIndex.ToString(), m_PageCount.ToString());
    }


    private void Update()
    {
        
        if (m_IsTouching)
        {
            if (!m_IsSaveBeforeTouch) {
                m_IsSaveBeforeTouch = true;
                m_FrontPanelPageIndex = m_PageIndex;
            }
            
            if (m_TouchDelta > 0)
            {
                if (!m_HasPrevious && m_FrontPanelPageIndex > 1)
                {
                    m_HasNext = false;
                    m_HasPrevious = true;
                    TouchPrevious();
                }
                if (m_DoPrevious)
                {
                    m_IsBackPageIndex = false;
                    m_BackPanel.localPosition = Vector3.Lerp(m_PrePos, m_CenterPos, Mathf.Abs(m_TouchDelta));
                    m_BackPanel.GetComponent<CanvasGroup>().alpha = Mathf.Abs(m_TouchDelta);
                }
                m_FrontPanel.localPosition = Vector3.Lerp(m_CenterPos, m_NextPos, Mathf.Abs(m_TouchDelta));
                m_FrontPanel.GetComponent<CanvasGroup>().alpha = 1 - Mathf.Abs(m_TouchDelta);
            }
            else if (m_TouchDelta < 0)
            {
                if (!m_HasNext && m_FrontPanelPageIndex < m_PageCount)
                {
                    m_HasNext = true;
                    m_HasPrevious = false;
                    TouchNext();
                }
                if (m_DoNext)
                {
                    m_IsBackPageIndex = false;
                    m_BackPanel.localPosition = Vector3.Lerp(m_NextPos, m_CenterPos, Mathf.Abs(m_TouchDelta));
                    m_BackPanel.GetComponent<CanvasGroup>().alpha = Mathf.Abs(m_TouchDelta);
                }
                m_FrontPanel.localPosition = Vector3.Lerp(m_CenterPos, m_PrePos, Mathf.Abs(m_TouchDelta));
                m_FrontPanel.GetComponent<CanvasGroup>().alpha = 1 - Mathf.Abs(m_TouchDelta);
            }
        }
        else {
            m_HasNext = false;
            m_HasPrevious = false;
            m_IsSaveBeforeTouch = false;
            float a = Mathf.Abs(m_FrontPanel.localPosition.y - m_CenterPos.y) / m_FadeDistance;
            m_CurrAlpha = a;
            if (m_TouchDelta >= 0.5f)
            {
                //float a = Mathf.Abs(m_FrontPanel.localPosition.y - m_CenterPos.y) / m_FadeDistance;
                if (m_DoPrevious)
                {
                    m_BackPanel.localPosition = Vector3.Lerp(m_BackPanel.localPosition, m_CenterPos, m_MoveSpeed * Time.deltaTime);
                    m_BackPanel.GetComponent<CanvasGroup>().alpha = a;

                    m_FrontPanel.localPosition = Vector3.Lerp(m_FrontPanel.localPosition, m_NextPos, m_MoveSpeed * Time.deltaTime);
                    m_FrontPanel.GetComponent<CanvasGroup>().alpha = 1 - a;
                    if (1 - a < 0.01f)
                    {
                        m_TouchDelta = 0;
                        SwitchPanel();
                    }
                }
                else {
                    m_TouchDelta = 0;
                }
                
            }
            else if (m_TouchDelta <= -0.5f)
            {
                //float a = Mathf.Abs(m_FrontPanel.localPosition.y - m_CenterPos.y) / m_FadeDistance;
                if (m_DoNext)
                {
                    m_BackPanel.localPosition = Vector3.Lerp(m_BackPanel.localPosition, m_CenterPos, m_MoveSpeed * Time.deltaTime);
                    m_BackPanel.GetComponent<CanvasGroup>().alpha = a;

                    m_FrontPanel.localPosition = Vector3.Lerp(m_FrontPanel.localPosition, m_PrePos, m_MoveSpeed * Time.deltaTime);
                    m_FrontPanel.GetComponent<CanvasGroup>().alpha = 1 - a;
                    if (1 - a < 0.01f)
                    {
                        m_TouchDelta = 0;
                        SwitchPanel();
                    }
                }
                else {
                    m_TouchDelta = 0;
                }
                
            }
            else {
                //float a = Mathf.Abs(m_FrontPanel.localPosition.y - m_CenterPos.y) / m_FadeDistance;
                if (m_DoPrevious)
                {
                    if (!m_IsBackPageIndex) {
                        m_IsBackPageIndex = true;
                        m_PageIndex = m_FrontPanelPageIndex;
                    }
                    if (m_PageIndex < m_PageCount && m_PageIndex > 1) {
                        m_BackPanel.localPosition = Vector3.Lerp(m_BackPanel.localPosition, m_PrePos, m_MoveSpeed * Time.deltaTime);
                        m_BackPanel.GetComponent<CanvasGroup>().alpha = a;
                    }
                    
                }
                else if (m_DoNext) {
                    if (!m_IsBackPageIndex)
                    {
                        m_IsBackPageIndex = true;
                        m_PageIndex = m_FrontPanelPageIndex;
                    }
                    if (m_PageIndex < m_PageCount && m_PageIndex > 1) {
                        m_BackPanel.localPosition = Vector3.Lerp(m_BackPanel.localPosition, m_NextPos, m_MoveSpeed * Time.deltaTime);
                        m_BackPanel.GetComponent<CanvasGroup>().alpha = a;
                    }
                    
                }
                m_FrontPanel.localPosition = Vector3.Lerp(m_FrontPanel.localPosition,m_CenterPos, m_MoveSpeed * Time.deltaTime);
                m_FrontPanel.GetComponent<CanvasGroup>().alpha = 1 - a;

                if (m_TouchDelta != 0 && a < 0.01f)
                {
                    m_TouchDelta = 0;
                    m_DoNext = false;
                    m_DoPrevious = false;
                    m_CanChangePage = true;
                }
            }
        }
    }


    private void SwitchPanel() {
        m_DoPrevious = false;
        m_DoNext = false;

        Transform temp = m_FrontPanel;
        m_FrontPanel = m_BackPanel;
        m_BackPanel = temp;

        m_CanChangePage = true;
    }

    public void OnNextBtnClick() {
        if (!m_CanChangePage) return;
        m_TouchDelta = -0.6f;

        Next();
    }

    /// <summary>
    /// 下一页
    /// </summary>
    public void Next()
    {
        if (m_PageCount <= 0)
            return;
        //最后一页禁止向后翻页
        if (m_PageIndex >= m_PageCount)
            return;

        m_CanChangePage = false;

        m_PageIndex += 1;
        if (m_PageIndex >= m_PageCount)
            m_PageIndex = m_PageCount;
        
        m_BackPanel.localPosition = m_NextPos;
        BindPage(m_BackPanel, m_PageIndex);

        m_DoNext = true;
        m_DoPrevious = false;
        
        //更新界面页数
        m_PanelText.text = string.Format("{0}/{1}", m_PageIndex.ToString(), m_PageCount.ToString());
    }

    /// <summary>
    /// 下一页
    /// </summary>
    public void TouchNext()
    {
        if (m_PageCount <= 0)
            return;
        //最后一页禁止向后翻页
        if (m_FrontPanelPageIndex >= m_PageCount)
            return;

        m_CanChangePage = false;

        m_PageIndex = m_FrontPanelPageIndex + 1;
        if (m_PageIndex >= m_PageCount)
            m_PageIndex = m_PageCount;

        m_BackPanel.localPosition = m_NextPos;
        BindPage(m_BackPanel, m_PageIndex);

        m_DoNext = true;
        m_DoPrevious = false;

        //更新界面页数
        m_PanelText.text = string.Format("{0}/{1}", m_PageIndex.ToString(), m_PageCount.ToString());
    }

    public void OnPreviousBtnClick() {
        if (!m_CanChangePage) return;
        m_TouchDelta = 0.6f;
        Previous();
    }
    /// <summary>
    /// 上一页
    /// </summary>
    public void Previous()
    {
        if (m_PageCount <= 0)
            return;
        //第一页时禁止向前翻页
        if (m_PageIndex <= 1)
            return;
        m_CanChangePage = false;

        m_PageIndex -= 1;
        if (m_PageIndex < 1)
            m_PageIndex = 1;

        m_BackPanel.localPosition = m_PrePos;
        BindPage(m_BackPanel, m_PageIndex);
        m_DoPrevious = true;
        m_DoNext = false;
        
        //更新界面页数
        m_PanelText.text = string.Format("{0}/{1}", m_PageIndex.ToString(), m_PageCount.ToString());
    }

    /// <summary>
    /// 上一页
    /// </summary>
    public void TouchPrevious()
    {
        if (m_PageCount <= 0)
            return;
        //第一页时禁止向前翻页
        if (m_FrontPanelPageIndex <= 1)
            return;
        m_CanChangePage = false;

        m_PageIndex = m_FrontPanelPageIndex -1;
        if (m_PageIndex < 1)
            m_PageIndex = 1;

        m_BackPanel.localPosition = m_PrePos;
        BindPage(m_BackPanel, m_PageIndex);
        m_DoPrevious = true;
        m_DoNext = false;

        //更新界面页数
        m_PanelText.text = string.Format("{0}/{1}", m_PageIndex.ToString(), m_PageCount.ToString());
    }

    /// <summary>
    /// 绑定指定索引处的页面元素
    /// </summary>
    /// <param name="index">页面索引</param>
    private void BindPage(Transform tran,int index)
    {
        //列表处理
        if (m_ItemsList == null || m_ItemsCount <= 0)
            return;

        //索引处理
        if (index < 0 || index > m_ItemsCount)
            return;

        //按照元素个数可以分为1页和1页以上两种情况
        if (m_PageCount == 1)
        {
            int canDisplay = 0;
            for (int i = m_PerPageCount; i > 0; i--)
            {
                if (canDisplay < m_PerPageCount && canDisplay< m_ItemsList.Count)
                {
                    BindGridItem(tran.GetChild(canDisplay), m_ItemsList[m_PerPageCount - i]);
                    tran.GetChild(canDisplay).gameObject.SetActive(true);
                }
                else
                {
                    //对超过canDispaly的物体实施隐藏
                    tran.GetChild(canDisplay).gameObject.SetActive(false);
                }
                canDisplay += 1;
            }
        }
        else if (m_PageCount > 1)
        {
            //1页以上需要特别处理的是最后1页
            //和1页时的情况类似判断最后一页剩下的元素数目
            //第1页时显然剩下的为12所以不用处理
            if (index == m_PageCount)
            {
                int canDisplay = 0;
                for (int i = m_PerPageCount; i > 0; i--)
                {
                    //最后一页剩下的元素数目为 m_ItemsCount - 12 * (index-1)
                    if (canDisplay < m_ItemsCount - m_PerPageCount * (index - 1))
                    {
                        BindGridItem(tran.GetChild(canDisplay), m_ItemsList[m_PerPageCount * index - i]);
                        tran.GetChild(canDisplay).gameObject.SetActive(true);
                    }
                    else
                    {
                        //对超过canDispaly的物体实施隐藏
                        tran.GetChild(canDisplay).gameObject.SetActive(false);
                    }
                    canDisplay += 1;
                }
            }
            else
            {
                for (int i = m_PerPageCount; i > 0; i--)
                {
                    BindGridItem(tran.GetChild(m_PerPageCount - i), m_ItemsList[m_PerPageCount * index - i]);
                    tran.GetChild(m_PerPageCount - i).gameObject.SetActive(true);
                }
            }
        }
    }


    /// <summary>
    /// 加载一个Sprite
    /// </summary>
    /// <param name="assetName">资源名称</param>
    private Sprite LoadSprite(string assetName)
    {
        Texture texture = (Texture)Resources.Load(assetName);

        Sprite sprite = Sprite.Create((Texture2D)texture, new Rect(0, 0, texture.width, texture.height), new Vector2(0.5f, 0.5f));
        return sprite;
    }

    /// <summary>
    /// 将一个GridItem实例绑定到指定的Transform上
    /// </summary>
    /// <param name="trans"></param>
    /// <param name="gridItem"></param>
    private void BindGridItem(Transform trans, GridItem gridItem)
    {
        //trans.GetComponent<Image>().sprite = LoadSprite(gridItem.ItemSprite);
        trans.GetComponent<Text>().text = gridItem.cnName;
        
    }
}