WinForm DataGridView 綁定泛型List(List<T>)/ArrayList不顯示的原因和解決

背景：無意間遇到了一個不大不小的問題，希望對一些遇到的人有所幫助！

一、問題

WinForm DataGridView 綁定泛型List (List<T>)/ArrayList不顯示，UI

代碼如下：

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、解決方法

其實很簡單，只是很多朋友可能沒有考慮到，因為這壓根不是什麼泛型List或者ArrayList的問題，

只要改代碼：

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

為：

    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、簡單講解

沒定義get、set的是欄位，定義了就是屬性了，為了安全性考慮，DataGridView 的數據源綁定只能是被公開了的屬性，而無權訪問欄位。很多其他控制項也有同樣的情況。