c# - 将文件反序列化为 List C#

Question

我正在尝试将包含对象的文件反序列化为对象列表但对于某些列表如何仅适用于对象这是我的代码:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.IO;
using System.Runtime.Serialization;
using System.Runtime.Serialization.Formatters.Binary;

namespace Test
{
    class Program
    {
        static void Main(string[] args)
        {
            user lastuser = new user("First name", "Last name", "Username", "Password");
            FileStream ToStream = new FileStream("UsersDB.txt", FileMode.OpenOrCreate);
            BinaryFormatter Ser = new BinaryFormatter();
            List<user> ToUsers = new List<user>();

            try
            {
                ToUsers = (List<user>)Ser.Deserialize(ToStream); // this is to deserialize everything in the file to the list
                ToUsers.Add(lastuser); // here we are adding our object (which is lastuser) to the list
                Ser.Serialize(ToStream, ToUsers); // here we are serializing the list back to the file
            }
            catch (System.Runtime.Serialization.SerializationException)
            {//this is to catch the exception if the file was empty and there is nth to deserialize to the list
                ToUsers.Add(lastuser);
                Ser.Serialize(ToStream, ToUsers);
            }
            ToStream.Close();

            Console.WriteLine("ToUsers objects : " + ToUsers.Count());
            // this is to see how many objects does the list have
        }
    }
}

这是我正在序列化的类:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Runtime.Serialization;

namespace Test
{
    [Serializable]
    class user
    {
        private string Fname, Lname, Username, Password;

        public user()
        { }

        public user(string Fname, string Lname, string Username, string Password)
        {
            this.Fname = Fname;
            this.Lname = Lname;
            this.Username = Username;
            this.Password = Password;
        }

        public string GetUsername()
        {
            return Username;
        }

    }
}

当我运行它时，我得到列表的计数是 1。

再次运行我明白了 2.

运行 1000 次，您将得到 2 个。

我知道有问题所以请帮助我。

Answer 1

你在 try 中的代码是

  try
  {
      ToUsers = (List<user>)Ser.Deserialize(ToStream);
      ToUsers.Add(lastuser);
      Ser.Serialize(ToStream, ToUsers);
  }

上面代码中发生的事情是，在反序列化过程中，流位置指针被移动到文件末尾。因此，当您向后序列化时，包含这两个对象的列表将追加到文件末尾。

因此，新的文件结构是这样的

 +---------------------+-----------------------------------------------------+
 | List (1 user info)  |    List (2 user's info)                             |
 +---------------------+-----------------------------------------------------+

因此，当您下次反序列化时，您会再次获得包含一个用户详细信息的列表。

要覆盖现有数据，请使用以下命令将流位置指针重置为文件开头

ToStream.Seek(0, SeekOrigin.Begin);

因此，您的 try block 看起来像

  try
  {
      ToUsers = (List<user>)Ser.Deserialize(ToStream);
      ToStream.Seek(0, SeekOrigin.Begin);

      ToUsers.Add(lastuser);
      Ser.Serialize(ToStream, ToUsers);
  }