浅谈ASP.NET Core 2.0 带初始参数的中间件(译)

public class GreetingOptions
{
  public string GreetAt { get; set; }
  public string GreetTo { get; set; }
}

public class GreetingMiddleware
{
  private readonly RequestDelegate _next;
  private readonly GreetingOptions _options;

  public GreetingMiddleware(RequestDelegate next, GreetingOptions options)
  {
    _next = next;
    _options = options;
  }

  public async Task Invoke(HttpContext context)
  {
    var message = $"Good {_options.GreetAt} {_options.GreetTo}";
    await context.Response.WriteAsync(message);
  }
}

public static IApplicationBuilder UseGreetingMiddleware(this IApplicationBuilder app, GreetingOptions options)
{
  return app.UseMiddleware<GreetingMiddleware>(options);
}

public void Configure(IApplicationBuilder app, IHostingEnvironment env)
{
  app.UseGreetingMiddleware(new GreetingOptions {
    GreetAt = "Morning",
    GreetTo = "Tahir"
  });
}

public static IApplicationBuilder UseGreetingMiddlewareAction(this IApplicationBuilder app, Action<GreetingOptions> optionsAction)
{
  var options = new GreetingOptions();
  optionsAction(options);

  return app.UseMiddleware<GreetingMiddleware>(options);
}

public void Configure(IApplicationBuilder app, IHostingEnvironment env)
{
  app.UseGreetingMiddlewareAction(options =>
  {
    options.GreetAt = "Morning";
    options.GreetTo = "Tahir";
  });
}

public interface IMessageService
{
  string FormatMessage(string message);
}

public class MessageService : IMessageService
{
  private readonly GreetingOptions _options;

  public MessageService(GreetingOptions options)
  {
    _options = options;
  }

  public string FormatMessage(string message)
  {
    return $"Good {_options.GreetAt} {_options.GreetTo} - {message}";
  }
}

public static IServiceCollection AddMessageService(this IServiceCollection services, GreetingOptions options)
{
  return services.AddScoped<IMessageService>(factory => new MessageService(options));
}

public static IServiceCollection AddMessageServiceAction(this IServiceCollection services, Action<GreetingOptions> optionsAction)
{
  var options = new GreetingOptions();
  optionsAction(options);

  return services.AddScoped<IMessageService>(factory => new MessageService(options));
}

public void ConfigureServices(IServiceCollection services)
{
  services.AddMessageService(new GreetingOptions
  {
    GreetAt = "Morning",
    GreetTo = "Tahir"
  });

  services.AddMessageServiceAction(options =>
  {
    options.GreetAt = "Morning";
    options.GreetTo = "Tahir";
  });
}

public void Configure(IApplicationBuilder app, IHostingEnvironment env, IMessageService msg)
{
  app.Run(async (context) =>
  {
    await context.Response.WriteAsync(msg.FormatMessage("by sanshi"));
  });
}