拖动ui限制区域

 将以下脚本挂在被拖拽的ui上，container为限制的区域Rect

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

public class Drag_move : MonoBehaviour, IBeginDragHandler, IDragHandler
{

    [Header("另一个UI =限制的区域")]
    public RectTransform container;

    RectTransform rt;
    // 位置偏移量
    Vector3 offset = Vector3.zero;
    // 最小、最大X、Y坐标
    float minX, maxX, minY, maxY;

    private Canvas canvas;
    void Start()
    {
        rt = GetComponent<RectTransform>();
        canvas = FindObjectOfType<Canvas>();
    }

    public void OnBeginDrag(PointerEventData eventData)
    {
        if (eventData.button != PointerEventData.InputButton.Left)
            return;
        if (RectTransformUtility.ScreenPointToWorldPointInRectangle(rt, eventData.position, eventData.enterEventCamera, out Vector3 globalMousePos))
        {
            // 计算偏移量
            offset = rt.position  - globalMousePos;
            // 设置拖拽范围
            SetDragRange();
        }      
    }
    public void OnDrag(PointerEventData eventData)
    {
        if (eventData.button != PointerEventData.InputButton.Left)
            return;
        // 将屏幕空间上的点转换为位于给定RectTransform平面上的世界空间中的位置
        if (RectTransformUtility.ScreenPointToWorldPointInRectangle(rt, eventData.position, eventData.pressEventCamera, out Vector3 globalMousePos))
        {
            rt.position = DragRangeLimit(globalMousePos + offset);
        }
    }

    // 设置最大、最小坐标
    void SetDragRange()
    {
        // 最小x坐标 = 容器当前x坐标 - 容器轴心距离左边界的距离 + UI轴心距离左边界的距离
        minX = container.position.x
            - container.pivot.x * container.rect.width* canvas.scaleFactor
            + rt.rect.width * canvas.scaleFactor * rt.pivot.x;
        // 最大x坐标 = 容器当前x坐标 + 容器轴心距离右边界的距离 - UI轴心距离右边界的距离
        maxX = container.position.x
            + (1 - container.pivot.x) * container.rect.width * canvas.scaleFactor
            - rt.rect.width * canvas.scaleFactor * (1 - rt.pivot.x);

        // 最小y坐标 = 容器当前y坐标 - 容器轴心距离底边的距离 + UI轴心距离底边的距离
        minY = container.position.y
            - container.pivot.y * container.rect.height * canvas.scaleFactor
            + rt.rect.height * canvas.scaleFactor * rt.pivot.y;

        // 最大y坐标 = 容器当前x坐标 + 容器轴心距离顶边的距离 - UI轴心距离顶边的距离
        maxY = container.position.y
            + (1 - container.pivot.y) * container.rect.height * canvas.scaleFactor
            - rt.rect.height * canvas.scaleFactor * (1 - rt.pivot.y);
    }
    // 限制坐标范围
    Vector3 DragRangeLimit(Vector3 pos)
    {
        pos.x = Mathf.Clamp(pos.x, minX, maxX);
        pos.y = Mathf.Clamp(pos.y, minY, maxY);
        return pos;
    }
}

第二种方式

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

public class DragWinSet : MonoBehaviour,IPointerDownHandler,IDragHandler
{
    private Vector2 localMousePos;
    private Vector3 planeLocalPos;
    private RectTransform targetObject;
    private RectTransform parentRectTransform;
    private RectTransform targetRectTransform;
    void Awake()
    {
        targetObject = this.transform.GetComponent<RectTransform>();
        targetRectTransform = targetObject;
        parentRectTransform = targetObject.parent as RectTransform;
    }
    private void Start()
    {
        
    }
    public void OnPointerDown(PointerEventData eventData)
    {
        planeLocalPos = targetRectTransform.localPosition;
        RectTransformUtility.ScreenPointToLocalPointInRectangle(parentRectTransform, eventData.position, eventData.pressEventCamera, out localMousePos);
        targetObject.gameObject.transform.SetAsLastSibling();
    }

    public void OnDrag(PointerEventData eventData)
    {
        Vector2 localPointerPosition;
        //屏幕点到矩形中的局部点
        if (RectTransformUtility.ScreenPointToLocalPointInRectangle(parentRectTransform, eventData.position, eventData.pressEventCamera, out localPointerPosition))
        {
            Vector3 offsetToOriginal = localPointerPosition - localMousePos;
            //targetObject.localPosition = planeLocalPos + offsetToOriginal;


            float x_right = Screen.width / SystemParameter.canvasScaler * 0.5f - targetObject.rect.width * 0.5f;
            float x_left = targetObject.rect.width * 0.5f - Screen.width / SystemParameter.canvasScaler * 0.5f;
            float y_up = Screen.height / SystemParameter.canvasScaler * 0.5f - targetObject.rect.height * 0.5f;
            float y_down = targetObject.rect.height * 0.5f - Screen.height / SystemParameter.canvasScaler * 0.5f;



            targetObject.localPosition = DragRangeLimit(planeLocalPos + offsetToOriginal, x_right, x_left, y_up, y_down);
        }
    }
    Vector3 DragRangeLimit(Vector3 pos, float x_right, float x_left, float y_up, float y_down)
    {
        pos.x = Mathf.Clamp(pos.x, x_left, x_right);
        pos.y = Mathf.Clamp(pos.y, y_down, y_up);
        return pos;
    }


}