1. Events can only be defined inside a class, while delegates can be defined inside or outside a class. Event definitions report errors externally

2. Delegates and events can be called indirectly in other classes. However, in an external class, the delegate can = a method, while the event cannot, only + = a method. Events can only be triggered inside the defined class, while delegates can be triggered in other external class calls.

using UnityEngine;
using System.Collections;
using System;
public delegate void OnClickHandler();
public class MyDelateStudy : MonoBehaviour {
    public OnClickHandler OnClickDelate;
    public event OnClickHandler OnClickEvent;
    private void Awake()
    {
        OnClickDelate += OnClickDelateFun;
        OnClickEvent+= OnClickEventFun;
    }
    private void OnDestroy()
    {
    }
    private void OnClickDelateFun()
    {
        Debug .Log ("MyDelateStudy----OnClickFunDelateFun implement");
    }
    private void OnClickEventFun()
    {
        Debug.Log("MyDelateStudy----OnClickFunEventFun implement");
    }
    private void Update()
    {
        if(Input.GetKeyDown (KeyCode.D))
        {
            if(OnClickDelate !=null )
             OnClickDelate();
        }

        if(Input .GetKeyDown (KeyCode.E ))
        {
            if(OnClickEvent !=null )
            {
                OnClickEvent();
            }
        }
    }
}

In mydeletestudy.cs, both the delegate onclickdelete and the event OnClickEvent can be monitored by + = a method in another class mydeletestudy2.

using UnityEngine;
using System.Collections;
using System;

public class MyDelateStudy2 : MonoBehaviour {

    MyDelateStudy my1;
    void Start ()
    {
        my1 = GetComponent<MyDelateStudy>();
        my1.OnClickDelate += OnClickFunDelateFun;
        my1.OnClickEvent += OnClickEventFun;
    }

    private void OnClickFunDelateFun()
    {
        Debug.Log("MyDelateStudy2---OnClickFunDelate fun implement");
    }
    private void OnClickEventFun()
    {
        Debug.Log("MyDelateStudy2----OnClickFunEventFun implement");
    }
    // Update is called once per frame
    void Update ()
    {

    }
}

A. But the event cannot be sufficient in the external class = a method, which can be used in the class defining the event

B. Events can only be triggered inside the defined class, while delegates can be triggered in other external class calls.