API Controllers routes isn't working on Blazor Server Side

Describe the bug

Defining routes / endpoints for API Controllers on a Blazor Server-Side project isn`t working. I had it working on previous Blazor versions but can’t it to work on 0.9.0-preview3-19154-02.

To Reproduce

startup.cs code:

        public void ConfigureServices(IServiceCollection services)
        {
   services.AddMvc().AddNewtonsoftJson().SetCompatibilityVersion(Microsoft.AspNetCore.Mvc.CompatibilityVersion.Version_3_0);
        services.AddRazorPages();
        services.AddServerSideBlazor();`

        //services.AddAuthentication(o => o.DefaultAuthenticateScheme = AzureADB2CDefaults.CookieScheme)
        //    .AddAzureADB2C(options => Configuration.Bind("AzureADB2C", options))
        //    .OnLogin(principal =>
        //    {
        //        services.BuildServiceProvider().GetRequiredService<LoginCommand>()
        //            .Execute(principal, principal.AzureID(), principal.Email(), principal.DisplayName());
        //    });

        services.AddBlazorModal();
        AddRepositories(services);
        AddCommands(services);
        AddHttpClient(services);
    }

    public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
    {

        app.UseHttpsRedirection();
        app.UseStaticFiles();
        //app.UseAuthentication();
        //app.UseMvcWithDefaultRoute();

        app.UseRouting();

        //app.UseMvc();

        //app.UseMvc(routes =>
        //{
        //    routes.MapRoute(
        //      name: "default",
        //      template: "{controller=Home}/{action}/{id?}");
        //});
        app.UseEndpoints(endpoints =>
        {
            endpoints.MapControllerRoute(
                name: "default",
                pattern: "{controller}/{action}");

            endpoints.MapControllers();
            //endpoints.MapRazorPages();

            endpoints.MapBlazorHub();
            endpoints.MapFallbackToPage("/_Host");
        });
    }

API Controller:

        [Produces("application/json")]
        [Route("api/[controller]")]
        [ApiController]
        public class DataController : Controller
        {
        [HttpPost]
        [Route("UploadPhoto")]
        public async Task<string> UploadFile(UploadFileParameters file)
        {
              return null;
        }

    [HttpGet]
    [Route("Test")]
    public string Test()
    {
        return "abc";
    }
}`

Expected behavior

Posting to https://localhost:xxxxx/api/Data/UploadPhoto Or getting from: https://localhost:xxxxx/api/Data/Test should work.

[iamgmd]

@baartho I installed VS2019 16.1.0 Preview 1.0 along with the nightly build of the dotnet SDK 3.0.100-preview4-011223, Created a BlazorComponent solution and changed the Startup.cs to be as below and I was able to call a MVC controller without problems. I will assume that this will work for an API controller as well. Hope this helps.

Startup.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading.Tasks;
using Microsoft.AspNetCore.Builder;
using Microsoft.AspNetCore.Hosting;
using Microsoft.AspNetCore.Http;
using Microsoft.AspNetCore.HttpsPolicy;
using Microsoft.AspNetCore.Mvc;
using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.Hosting;
using WebApplication1.Data;

namespace WebApplication1
{
    public class Startup
    {
        // This method gets called by the runtime. Use this method to add services to the container.
        // For more information on how to configure your application, visit https://go.microsoft.com/fwlink/?LinkID=398940
        public void ConfigureServices(IServiceCollection services)
        {
            services.AddMvc(options => options.EnableEndpointRouting = false)
                .SetCompatibilityVersion(CompatibilityVersion.Version_3_0);

            services.AddRazorPages();
            services.AddServerSideBlazor();
            services.AddSingleton<WeatherForecastService>();
        }

        // This method gets called by the runtime. Use this method to configure the HTTP request pipeline.
        public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
        {
            if (env.IsDevelopment())
            {
                app.UseDeveloperExceptionPage();
            }
            else
            {
                // The default HSTS value is 30 days. You may want to change this for production scenarios, see https://aka.ms/aspnetcore-hsts.
                app.UseHsts();
            }

            app.UseHttpsRedirection();

            app.UseStaticFiles();

            app.UseRouting();

            app.UseMvcWithDefaultRoute();

            app.UseEndpoints(endpoints =>
            {
                //endpoints.MapControllers();
                endpoints.MapBlazorHub();
                endpoints.MapFallbackToPage("/_Host");
            });
        }
    }
}

[natrist]

@iamgmd I managed to complete the first part of this tutorial (https://docs.microsoft.com/en-us/aspnet/core/tutorials/first-mvc-app/adding-controller?view=aspnetcore-3.0&tabs=visual-studio) following your code example.

This problem is still present with the latest out-of-the-box Visual Studio 2019 setup as of today. I’m not sure if it affects every project template, but I built mine with Blazor MVC and I had to add the lines from your comment for my controllers to work.