unity中利用layer的方式来获取指定层级上的对象，例如UI层的某个对象

1.按下鼠标左键，检测鼠标点击到的UI对象

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

public class CustomBookMouseController : MonoBehaviour {

    public LayerMask m_layerMask = 1;

    public float m_dis = 1000;

    public Camera m_rayCamera;
    
    
    // Update is called once per frame
    void Update () {
        if (Input.GetMouseButtonDown(0))
        {
            if (EventSystem.current.IsPointerOverGameObject())
            {
                PointerEventData pointerData = new PointerEventData(EventSystem.current);
                pointerData.position = Input.mousePosition;

                List<RaycastResult> results = new List<RaycastResult>();
                EventSystem.current.RaycastAll(pointerData, results);
                for (int i = 0; i < results.Count; i++)
                {
                    if (results[i].gameObject.layer==LayerMask.NameToLayer("BookUI"))
                    {
                        Debug.Log(results[i].gameObject.name);
                    }
                    Debug.Log(results[i].gameObject);
                }
            }

        }
    }
}

2.物理射线的应用 需要在检测对象上添加碰撞器组件

            var ray = m_rayCamera.ScreenPointToRay(Input.mousePosition);
            RaycastHit hitInfo;
            if (Physics.Raycast(ray, out hitInfo, m_dis, m_layerMask))
            {
                Debug.Log(hitInfo.collider.gameObject.name);
            }