本文主要内容参考自下面几篇博客，操作步骤只是为了做个备注方便回忆，具体细节和原理还是推荐大家自行阅读下面几篇博客：

• Dependency Injection in Windows Form or WPF Application .NET Core
• Dependency Injection in .NET Core Console app using Generic HostBuilder
• Loading Configuration (.INI,.XML,.JSON) in .NET Core Console or WinForm application – Part I

  操作步骤

  我的目标是在 .NET Core 3.1 WinForm 中注入官方自带的 Configuration、Logger 和 EF Core。

1. 新建 .NET Core 3.1 WinForm 项目
2. NuGet 安装 Microsoft.Extensions.Hosting

3. 配置 EF Core（这步可以参考官方的 ASP.NET Core 教程）

   1. NuGet 安装 EF Core 相关包
   2. 创建实体类

   3. 创建 DbContext

      public class K3DbContext : DbContext
      {
      public K3DbContext(DbContextOptions<K3DbContext> options) : base(options)
      {
      }
      public DbSet<XX> XXs { get; set; }
      }

4. 手动添加 appsettings.json 文件，并将其设置为总是复制到输出目录

   {
   "Logging": {
    "LogLevel": {
      "Default": "Information"
    }
   },
   "AllowedHosts": "*",
   "ConnectionStrings": {
    "K3Connection": "server=10.XX.XX.XXX;Database=K3;User ID=XX;Password=XX"
   }
   }

5. 修改 Main() 代码

   [STAThread]
   static void Main()
   {
    Application.SetHighDpiMode(HighDpiMode.SystemAware);
    Application.EnableVisualStyles();
    Application.SetCompatibleTextRenderingDefault(false);
    // CreateDefaultBuilder 里面自动注入并配置了 IConfiguration
    var hostBuilder = Host.CreateDefaultBuilder()
        .ConfigureServices((hostContext, services) =>
        {
            services.AddLogging(configure => configure.AddDebug());
            services.AddTransient<Form1>();
            services.AddDbContext<K3DbContext>(options =>
                options.UseSqlServer(hostContext.Configuration.GetConnectionString("K3Connection")));
        });
    var builderDefault = hostBuilder.Build();
    using (var serviceScope = builderDefault.Services.CreateScope())
    {
        var services = serviceScope.ServiceProvider;
        var form1 = services.GetRequiredService<Form1>();
        Application.Run(form1);
    }
   }

6. 在 Form1 中使用注入的实例

   public partial class Form1 : Form
   {
    private readonly IConfiguration _configuration;
    private readonly ILogger<Form1> _logger;
    public Form1(IConfiguration configuration, ILogger<Form1> logger)
    {
        _configuration = configuration;
        _logger = logger;
        InitializeComponent();
    }
    private void BtnHello_Click(object sender, EventArgs e)
    {
        Debug.WriteLine(_configuration.GetConnectionString("K3Connection"));
        //MessageBox.Show(".NET Core","Hello");
        _logger.LogInformation("Logger test");
    }
   }