WinForm DataGridView 绑定泛型List(List<T>)/ArrayList不显示的原因和解决

背景：无意间遇到了一个不大不小的问题，希望对一些遇到的人有所帮助！

一、问题

WinForm DataGridView 绑定泛型List (List<T>)/ArrayList不显示，UI

代码如下：

using System;
using System.Collections.Generic;
using System.Data;
using System.Data.OleDb;
using System.IO;
using System.Windows.Forms;

namespace WindowsFormsApplication1
{
    public delegate T BorrowReader<out T>(IDataReader reader);

    public partial class FormMain : Form
    {
        public FormMain()
        {
            InitializeComponent();
            
        }

        private List<User> GetUsers(IDataReader reader)
        {
            var list = new List<User>();
            while (reader.Read())
            {
                list.Add(new User()
                {
                    ID = reader.GetInt32(reader.GetOrdinal("ID")),
                    UserName = reader.GetString(reader.GetOrdinal("UserName")),
                    NickName = reader.GetString(reader.GetOrdinal("NickName")),
                    Phone = reader.GetString(reader.GetOrdinal("Phone")),
                    QQ = reader.GetString(reader.GetOrdinal("QQ")),
                });
            }
            return list;
        }

        private void btnTest_Click(object sender, EventArgs e)
        {
            dataGridView1.AutoGenerateColumns = false;
            var list = MyDb.LendReader("select * from Users where 0=0", GetUsers);
            dataGridView1.DataSource = list;
        }
    }

    public class User
    {
        public int ID;
        public string UserName;
        public string NickName;
        public string Phone;
        public string QQ;

    }

    public class MyDb
    {
        public static T LendReader<T>(string sql, BorrowReader<T> borrowReader)
        {
            using (OleDbConnection connection = CreateConnection())
            {
                connection.Open();
                OleDbCommand c = new OleDbCommand(sql, connection);
                OleDbDataReader r = c.ExecuteReader();
                return borrowReader(r);
            }
        }

        private static OleDbConnection CreateConnection()
        {
            string dbName = Path.Combine(Application.StartupPath, "MyData.mdb");
            OleDbConnection c = new OleDbConnection
            {
                ConnectionString = "Provider=Microsoft.Jet.OLEDB.4.0;Data Source=" + dbName
            };
            return c;
        }
    }
}

二、解决方法

其实很简单，只是很多朋友可能没有考虑到，因为这压根不是什么泛型List或者ArrayList的问题，

只要改代码：

    public class User
    {
        public int ID;
        public string UserName;
        public string NickName;
        public string Phone;
        public string QQ;
    }

为：

    public class User
    {
        public int ID{ get; set; }
        public string UserName { get; set; }
        public string NickName { get; set; }
        public string Phone { get; set; }
        public string QQ { get; set; } 
    }

就好了

三、简单讲解

没定义get、set的是字段，定义了就是属性了，为了安全性考虑，DataGridView 的数据源绑定只能是被公开了的属性，而无权访问字段。很多其他控件也有同样的情况。