remove multiple startup

[Rick-Anderson]

What's the purpose? I can't get this to work. See also #2511

[Rick-Anderson]

@Eilon please review. What's the intention here.

Main needs the correct NS to call Startup

public static void Main(string[] args)
        {
            var host = new WebHostBuilder()
                .UseKestrel()
                .UseContentRoot(Directory.GetCurrentDirectory())
                .UseIISIntegration()
                .UseStartup<Startup>()
                .Build();

            host.Run();
        }```

[ardalis]

I believe this behavior only works (worked?) if you didn't specify .UseStartup() or .UseStartup<T>() in WebHostBuilder.

[Rick-Anderson]

When I comment out /.UseStartup<Startup>(), I get
500 Internal Server Error No service for type 'Microsoft.AspNetCore.Hosting.IStartup' has been registered.

[ardalis]

Ah, that must've changed since the betas, then.

[Eilon]

@Tratcher can you comment on the behavior when there are multiple Startup classes, and which WebHostBuilder.UseStartupXYZ() method does what?

[Tratcher]

A long time ago there was a feature to scan assemblies for Startup if you didn't specify UseStartup. This was removed when we added UseStartup<T>

[Tratcher]

This whole feature has been removed. Call UseStartup<T>

[Rick-Anderson]

replaced by #2564