public  Button btn;
 void Start () {
        // 一、btn.onClick.AddListener(OnBtnClick);
        // 二、btn.onClick.AddListener(delegate () { OnBtnClick(); });
        btn.onClick.AddListener(() => {
            OnBtnClick();
        });
 } 
    void OnBtnClick()
    {
        Debug.Log("0000");
    }

using UnityEngine;
using System.Collections;
using System.Collections.Generic;
using UnityEngine.Events;
using UnityEngine.UI; 
public class ButtonOnClickTest: MonoBehaviour {
 
 // Use this for initialization
 void Start () {
  List<string> btnsName = new List<string>();
  btnsName.Add("BtnPlay");
  btnsName.Add("BtnShop");
  btnsName.Add("BtnLeaderboards");
 
  foreach(string btnName in btnsName)
  {
   GameObject btnObj = GameObject.Find(btnName);
   Button btn = btnObj.GetComponent<Button>();
   btn.onClick.AddListener(delegate() {
    this.OnClick(btnObj); 
   });
  } 
 }
 
 public void OnClick(GameObject sender)
 {
  switch (sender.name)
  {
  case "BtnPlay":
   Debug.Log("BtnPlay");
   break;
  case "BtnShop":
   Debug.Log("BtnShop");
   break;
  case "BtnLeaderboards":
   Debug.Log("BtnLeaderboards");
   break;
  default:
   Debug.Log("none");
   break;
  }
 }
 
 // Update is called once per frame
 void Update () {
 
 }
}