btnEvent.cs

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

public class OnClickBtnScript : MonoBehaviour {
	public Button btn;
	void Start () {
		btn.onClick.AddListener (OnClickBtnCallback);
	}
	
	void OnClickBtnCallback() {
		Debug.Log ("OnClickBtnCallback");
	}
}