1. 實現原理：
   它的原理就是利用ScrollRect來限制搖塊的搖動區域，但是ScrollRect是矩形的，我們的搖桿的搖動區域應該是個圓形的才對。所以順著這個思路我們可以寫個類繼承ScrollRect，自己稍做處理就ok

2. 例項展示：
   如下圖所示， ScrollCircleMove就是搖桿的背景， 裡面的Image就是搖桿塊。
   

3. 程式碼演示：

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

public
 
 class ScrollCircleMove : ScrollRect
{
    public float m_Speed = 10f;
    public GameObject m_Player;
    private Animator m_Animator;
    private Vector3 m_PlayerDir;//搖桿方向
    private bool m_bDrag = false;
    protected float m_Radius = 0f;

    protected override void Start()
    {
        base.Start();
        // 能移動的半徑 = 搖桿的寬 * Dis
 

        m_Radius = (transform as RectTransform).sizeDelta.x * 0.5f;

        m_Player = GameObject.FindGameObjectWithTag("Player");
        m_Animator = m_Player.GetComponent<Animator>();
        m_Speed = 5f;
    }

    public override void OnDrag(UnityEngine.EventSystems.PointerEventData eventData)
    {
        base
 
.OnDrag(eventData);
        // 獲取搖桿，根據錨點的位置
        var contentPostion = this.content.anchoredPosition;

        // 判斷搖桿的位置 是否大於 半徑
        if (contentPostion.magnitude > m_Radius)
        {
            // 設定搖桿最遠的位置
            contentPostion = contentPostion.normalized * m_Radius;
            SetContentAnchoredPosition(contentPostion);
        }

        // 獲取搖桿方向 
        m_PlayerDir = content.anchoredPosition.normalized;
    }

    public override void OnBeginDrag(PointerEventData eventData)
    {
        base.OnBeginDrag(eventData);
        m_bDrag = true;
        m_Animator.SetBool("Move", true);
    }

    public override void OnEndDrag(PointerEventData eventData)
    {
        base.OnEndDrag(eventData);
        m_bDrag = false;
        m_Animator.SetBool("Move", false);
    }

    void Update()
    {
        if (m_bDrag)
        {
            m_Player.GetComponent<Rigidbody>().MovePosition(m_Player.transform.position + new Vector3(m_PlayerDir.x, 0, m_PlayerDir.y) * Time.deltaTime * m_Speed);

        }
    }
}