第一个C#程序的坑爹问题

本菜初学C#了，有个小程序：MessageBox点是就显示窗体，否则结束

编译环境VS2012 .net 4.5

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;

namespace P7_1
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
            this.Load += Form1_Load;
        }

        void Form1_Load(object sender, EventArgs e)
        {
            DialogResult result = MessageBox.Show("kkk", "adf", MessageBoxButtons.OKCancel, MessageBoxIcon.Question);
            if (result == DialogResult.Cancel)
            {
                this.Close();
            }
            else if (result == DialogResult.OK)
            {
                this.FormClosing += Form1_FormClosing;
            }
        }

        void Form1_FormClosing(object sender, FormClosingEventArgs e)
        {
            if (MessageBox.Show("sadf", "adf", MessageBoxButtons.YesNo, MessageBoxIcon.Question, MessageBoxDefaultButton.Button2) == DialogResult.No)
            {
                e.Cancel = true;
            }
        }
    }
}

咦？为啥弹窗两次呢？

后来找大牛问了下，问题出在

this.Load += Form1_Load;

实际上，现在不填充Load成员也会跑一遍Form1_Load了，所以这行代码会导致MessageBox弹出两次