C#中委托与事件的原理是什么

using UnityEngine;
using System.Collections;
using UnityEngine.UI;
using System;
public class basetest : MonoBehaviour
{

  public GameObject panel;
  private bool isclick = false;
  public delegate void GreetingDelegate(int param);
  public event GreetingDelegate payxx;
  // Use this for initialization
  void Start()
  {

  }

  // Update is called once per frame
  void Update()
  {

  }
  void OnMouseOver()
  {
    if (Input.GetMouseButtonDown(0))
    { //左键点击
      Debug.LogError("你点击了NPC");
      //playRenwu();
    }

  }
  public void pay() {
    Debug.LogError("触发了委托");
  }

  void playRenwu(bool isnotclick)
  {
    Debug.LogError("开始NPC任务");
    panel.gameObject.SetActive(isnotclick);
  }


  //protected virtual void Onpayxxxxx(int param)
  //{
  //  if (payxx != null)
  //  {
  //    Debug.LogError("委托的事件触发了");
  //    payxx(param);
  //  }
  //  else
  //  {
  //    Debug.LogError("委托的事件没触发");
  //  }

  //}
  public void Onpayxx(int param)
  {
    if (payxx != null)
    {
      payxx(param);
    }
    else { 
    }
    
  }

  public void Myfuntion2(int param)
  {
    Debug.LogError("第二次调用=" + param);
  }
  public void MyFunction(int param)
  {
    Debug.LogError("OKOKOKOKO=" + param);
  }
  public void Onclickbutton()
  {
    basetest eventTest = new basetest();
    eventTest.payxx += new GreetingDelegate(MyFunction);//安装事件
    eventTest.payxx += new GreetingDelegate(Myfuntion2);//安装事件
    eventTest.Onpayxx(10);

    if (isclick == false)
    {
      Debug.LogError("你点击了按钮");
      isclick = true;
      playRenwu(true);
    }
    else
    {
      isclick = false;
      playRenwu(false);
    }
  }
}