ASP.NET Core 7 Web API inside Blazor Server project not working

Question

I am trying to add an ASP.NET Core 7 Web API inside the Blazor Server application, but the API is not loading.

When I go to this URL: https://localhost:44322/api/GetWeatherForecast, I see the following. Please let me know how to fix this.

Thanks!

Sorry, there's nothing at this address.

My API controller:

using BlazorAppWebAPI.Data;
using Microsoft.AspNetCore.Mvc;
using System.Web.Http;

namespace BlazorAppWebAPI.API
{
    [ApiController]
    [System.Web.Http.Route("api")]
    public class APIController : Controller
    {
        private static readonly string[] Summaries = new[]
        {"Freezing", "Bracing", "Chilly", "Cool", "Mild", "Warm", "Balmy", "Hot", "Sweltering", "Scorching"};

        private readonly ILogger<ApiController> _logger;

        public APIController(ILogger<ApiController> logger)
        {
            _logger = logger;
        }

        [Microsoft.AspNetCore.Mvc.HttpGet("GetWeatherForecast")]
        public IEnumerable<WeatherForecast> Get()
        {
            return Enumerable.Range(1, 5).Select(index => new WeatherForecast
            {
                Date = DateOnly.FromDateTime(DateTime.Now.AddDays(index)),
                TemperatureC = Random.Shared.Next(-20, 55),
                Summary = Summaries[Random.Shared.Next(Summaries.Length)]
            })
            .ToArray();
        }
    }
}

Program.cs:

using BlazorAppWebAPI.Data;
using Microsoft.AspNetCore.Components;
using Microsoft.AspNetCore.Components.Web;

var builder = WebApplication.CreateBuilder(args);

// Add services to the container.
builder.Services.AddRazorPages();
builder.Services.AddServerSideBlazor();
builder.Services.AddControllers();
builder.Services.AddSingleton<WeatherForecastService>();

var app = builder.Build();

// Configure the HTTP request pipeline.
if (!app.Environment.IsDevelopment())
{
    app.UseExceptionHandler("/Error");
    app.UseHsts();
}

app.UseHttpsRedirection();

app.UseStaticFiles();

app.UseRouting();

app.MapControllers();

app.MapBlazorHub();
app.MapFallbackToPage("/_Host");

app.Run();

WeatherForcast.cs:

namespace BlazorAppWebAPI.Data
{
    public class WeatherForecast
    {
        public DateOnly Date { get; set; }

        public int TemperatureC { get; set; }

        public int TemperatureF => 32 + (int)(TemperatureC / 0.5556);

        public string? Summary { get; set; }
    }
}

Answer 1

After checking the issue, I found System.Web.Http is the root cause. The System.Web.Http namespace does not exist in the ASP.Net Core.

Here is the correct step to add api in Blazor Server App.

Program.cs

using BlazorAppWebAPI.Data;
using Microsoft.AspNetCore.Components;
using Microsoft.AspNetCore.Components.Web;

namespace BlazorAppWebAPI
{
    public class Program
    {
        public static void Main(string[] args)
        {
            var builder = WebApplication.CreateBuilder(args);

            // Add services to the container.
            // add this line
            builder.Services.AddControllers();

            builder.Services.AddRazorPages();
            builder.Services.AddServerSideBlazor();
            builder.Services.AddSingleton<WeatherForecastService>();

            var app = builder.Build();

            // Configure the HTTP request pipeline.
            if (!app.Environment.IsDevelopment())
            {
                app.UseExceptionHandler("/Error");
                // 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();
            // add this line
            app.MapControllers();
            app.MapBlazorHub();
            app.MapFallbackToPage("/_Host");

            app.Run();
        }
    }
}

APIController.cs

using BlazorAppWebAPI.Data;
using Microsoft.AspNetCore.Mvc;

namespace BlazorAppWebAPI.API
{
    [ApiController]
    [Route("[controller]")]
    public class APIController : ControllerBase
    {
        private static readonly string[] Summaries = new[]
        {"Freezing", "Bracing", "Chilly", "Cool", "Mild", "Warm", "Balmy", "Hot", "Sweltering", "Scorching"};

        private readonly ILogger<APIController> _logger;

        public APIController(ILogger<APIController> logger)
        {
            _logger = logger;
        }

        [HttpGet("GetWeatherForecast")]
        public IEnumerable<WeatherForecast> Get()
        {
            return Enumerable.Range(1, 5).Select(index => new WeatherForecast
            {
                Date = DateTime.Now.AddDays(index),
                TemperatureC = Random.Shared.Next(-20, 55),
                Summary = Summaries[Random.Shared.Next(Summaries.Length)]
            })
            .ToArray();
        }
    }
}

Test Result