如何使用 CsvHelper 包将 C# 列表写入 CSV

Question

我有一个简单的控制台应用程序，其中包含 Program.cs 中 3 个用户的列表。在 Program.cs 中，我想调用 FileOperations.cs 中的一个方法。

首先我的Program.cs：

using System;
using System.Collections.Generic;
using System.IO;
using System.Text;
using CsvHelper;

namespace GimpiesConsoleOOcsvListUI
{
    class Program
    {
        static void Main(string[] args)
        {
            // Create user default instances
            User user0 = new User("Beheer", "beheer@gimpies.nl", "123");
            User user1 = new User("Inkoop", "inkoop@gimpies.nl", "123");
            User user2 = new User("Verkoop", "verkoop@gimpies.nl", "123");

            // List of users (with a list you can add, get and remove items in the list)
            List<User> users = new List<User>();
            users.Add(user0);
            users.Add(user1);
            users.Add(user2);

            // Create login instance
            LoginManager loginMgr = new LoginManager();

            Start:
            // Welcome message
            Console.WriteLine("Welcome to GimpiesTerminal! Choose 1 to login or 2 to register:");

            // Get input from user
            string input = Console.ReadLine();

            bool successfull = false;

            while (!successfull)
            {
                if(input == "1")
                {
                    Console.WriteLine("Enter your username:");
                    string username = Console.ReadLine();
                    Console.WriteLine("Enter your password:");
                    string password = Console.ReadLine();

                    foreach (User user in users)
                    {
                        if (username == user.UserName && password == user.PassWord)
                            {
                                Console.WriteLine("You have successfully logged in !!!");
                                Console.ReadLine();
                                successfull = true;
                            break;  
                            }
                    }
                        if (!successfull)
                            {
                                Console.WriteLine("Your username or password is incorrect, try again !!!");
                            }
                }
                else if (input == "2")
                {
                        // Get user input
                        Console.WriteLine("Enter your username:");
                        string username = Console.ReadLine();

                        Console.WriteLine("Enter your email:");
                        string email = Console.ReadLine();

                        Console.WriteLine("Enter your password:");
                        string password = Console.ReadLine();

                        // Create fresh instance to save input in memory
                        User user = new User(username, email, password);

                        // Adds the user to the excisting list
                        users.Add(user);
                        
                        successfull = true;
                        goto Start;
                }
                else if (input == "3")
                {
                    // Here I want to call the method from FileOperations.cs to write the List here to a CSV file.
                }
                else
                {
                    Console.WriteLine("Try again !!!");
                    break;
                }
            }
            
            // // Loop over stored users within instances inside the list where users are added
            // foreach (User user in users)
            // {
            
            //     if(loginMgr.Login(user))
            //     {
            //         // Login successfull
            //         Console.WriteLine("Login user " + user.UserName);

            //     }
            //     else
            //     {
            //         // Not successfull

            //     }
            // }  
            
        }
    }
}

这是我的FileOperations.cs：

using System;
using System.Collections.Generic;
using System.IO;
using System.Text;
using CsvHelper;

namespace GimpiesConsoleOOcsvListUI
{
    public class FileOperations
    {
        // Handles CRUD within CSV files and able to save them
        public void SaveToCSV(User user)
        {
            using (var mem = new MemoryStream())
            using (var writer = new StreamWriter(mem))
            using (var csvWriter = new CsvWriter(writer))
            {
                csvWriter.Configuration.Delimiter = ";";
                csvWriter.Configuration.HasHeaderRecord = true;
                csvWriter.Configuration.AutoMap<User>();

                csvWriter.WriteHeader<User>();
                csvWriter.WriteRecords(user);

                writer.Flush();
                var result = Encoding.UTF8.GetString(mem.ToArray());
                Console.WriteLine(result);
            }
        }
    } 
}

我在FileOperations.cs 的第 16 行收到以下错误：

StreamWriter 编写器 参数 1：无法从 System.IO.StreamWriter 转换为 CsvHelper.ISerializer

第 23 行：

用户用户 参数 1：无法从 GimpiesConsoleOOcsvListUI.User 转换为 System.Collections.IEnumerable

我是 C# 的新手，所以我希望你不介意它是否很容易解决问题！ :-)

Answer 1

您收到错误是因为您在两种情况下都传递了错误的参数类型。 CsvWriter 没有构造函数，它只接受一个参数是 TextWriter。我对这个库不是很熟悉，但我相信它可能在过去做过。我怀疑您从互联网上的先前示例中复制了您的代码，这些示例已过时。

解决这个问题的简单方法是添加另外两个参数：

using (var csvWriter = new CsvWriter(writer, CultureInfo.CurrentCulture, false))

第二个错误是因为CsvWriter.WriteRecords 需要一个IEnumerable 参数，而不是单个实例。要解决此问题，您需要将List<User> 传递给它，因此整个代码变为：

public void SaveToCSV(List<User> users)
{
    using (var mem = new MemoryStream())
    using (var writer = new StreamWriter(mem))
    using (var csvWriter = new CsvWriter(writer, CultureInfo.CurrentCulture, false))
    {
        csvWriter.Configuration.Delimiter = ";";
                
        csvWriter.Configuration.HasHeaderRecord = true;
        csvWriter.Configuration.AutoMap<User>();

        csvWriter.WriteHeader<User>();
        csvWriter.WriteRecords(users);

        writer.Flush();
        var result = Encoding.UTF8.GetString(mem.ToArray());
        Console.WriteLine(result);
    }
}

Answer 2

如果您想序列化单个用户对象并显示其序列化的标头和值，可以尝试以下代码：

public void SaveToCSV(User user)
{
    using (var writer = new StringWriter())
    using (var csvWriter = new CsvWriter(writer, CultureInfo.InvariantCulture, leaveOpen: true))
    {
        csvWriter.Configuration.Delimiter = ";";
        csvWriter.Configuration.HasHeaderRecord = true;
        csvWriter.Configuration.AutoMap<User>();

        csvWriter.WriteHeader<User>();
        csvWriter.WriteRecord(user);
        csvWriter.Flush();

        var result = writer.ToString();
        Console.WriteLine(result);
    }
}

它使用库的CsvWriter 所需的简单StringWriter 实例，并使用InvariantCulture 信息进行内容序列化。在这种情况下，第三个参数leaveOpen 必须设置为true，因为您对using 块范围内的StringWriter 的内容感兴趣。最后但同样重要的是，您当前正在传递 User 的单个实例，因此您必须调用 WriteRecord 方法而不是 WriteRecords。

如果你想将它写入实际文件，你必须做一些不同的事情：

public void SaveToCSV(User user)
{
    using (var writer = new StreamWriter("path\\to\\your\\file.csv"))
    using (var csvWriter = new CsvWriter(writer, CultureInfo.InvariantCulture))
    {
        csvWriter.Configuration.Delimiter = ";";
        csvWriter.Configuration.HasHeaderRecord = true;
        csvWriter.Configuration.AutoMap<User>();

        csvWriter.WriteHeader<User>();
        csvWriter.WriteRecord(user);
    }
}

您不需要在第二个示例中调用 Flush，因为 using 块的末尾会为您调用它，而您对其范围内的 CSV 内容不感兴趣。