C#中的依赖注入Dependency Injection DI的实现步骤

// 定义接口
public interface IMyService
{
    string GetMessage();
}

// 实现接口
public class MyService : IMyService
{
    public string GetMessage() => "Hello from MyService!";
}

var builder = WebApplication.CreateBuilder(args);

// 注册服务（生命周期可选）
builder.Services.AddTransient<IMyService, MyService>();      // 瞬时
builder.Services.AddScoped<IMyService, MyService>();         // 作用域
builder.Services.AddSingleton<IMyService, MyService>();      // 单例

// 直接注册类（无接口）
builder.Services.AddTransient<MyService>();

public class MyController : ControllerBase
{
    private readonly IMyService _service;

    // 构造函数自动注入
    public MyController(IMyService service)
    {
        _service = service;
    }

    [HttpGet]
    public IActionResult Get()
    {
        return Ok(_service.GetMessage());
    }
}

Install-Package Microsoft.Extensions.DependencyInjection

public partial class App : Application
{
    public IServiceProvider ServiceProvider { get; private set; }

    protected override void OnStartup(StartupEventArgs e)
    {
        var services = new ServiceCollection();
        
        // 注册服务
        services.AddTransient<IMyService, MyService>();
        services.AddSingleton<MainWindow>(); // 注册主窗口

        ServiceProvider = services.BuildServiceProvider();
        
        // 解析主窗口并显示
        var mainWindow = ServiceProvider.GetRequiredService<MainWindow>();
        mainWindow.Show();
    }
}

public partial class MainWindow : Window
{
    public MainWindow(IMyService service)
    {
        InitializeComponent();
        var message = service.GetMessage(); // 使用注入的服务
    }
}

// 注册多个实现
builder.Services.AddTransient<IMyService, ServiceA>();
builder.Services.AddTransient<IMyService, ServiceB>();

// 通过 IEnumerable<T> 获取所有实现
public class Consumer
{
    public Consumer(IEnumerable<IMyService> services)
    {
        foreach (var service in services)
        {
            service.DoSomething();
        }
    }
}

builder.Services.AddTransient<IMyService>(provider => 
{
    var config = provider.GetRequiredService<IConfiguration>();
    return new MyService(config.GetValue<string>("Mode"));
});

System.InvalidOperationException: No service for type 'IMyService' has been registered.