internal static class Program
 {
     /// <summary>
     /// 應用程序的主入口點。
     /// </summary>
     [STAThread]
     static void Main()
     {
         //創建服務容器
         var services = new ServiceCollection();
         //添加服務注冊
         ConfigureServices(services);
         //先用DI容器生成 serviceProvider, 然后通過 serviceProvider 獲取Main Form的注冊實例
         var serviceProvider = services.BuildServiceProvider();
         var formMain = serviceProvider.GetRequiredService<MainForm>();   //主動從容器中獲取FormMain實例, 這是簡潔寫法
         // var formMain = (FormMain)serviceProvider.GetService(typeof(FormMain));  //更繁瑣的寫法
         Application.Run(formMain);
     }
     /// <summary>
     /// 注入服務
     /// </summary>
     /// <param name="services"></param>
     public static void ConfigureServices(IServiceCollection services)
     {
         services.AddSingleton<ILoginService, LoginService>();
         services.AddScoped(typeof(MainForm));
     }
 }

 public interface ILoginService
 {
     void Login(string username, string password);
 }

 public class LoginService : ILoginService
 {
     public void Login(string username, string password)
     {
         MessageBox.Show("登錄成功!");
     }
 }

 public partial class MainForm : Form
 {
     private readonly ILoginService _loginService;
     public MainForm(ILoginService loginService)
     {
         InitializeComponent();
         _loginService = loginService;
     }

     private void button1_Click(object sender, EventArgs e)
     {
         _loginService.Login("uname","pwd");
     }
 }