Hosting ASP.NET Core API in a Windows Forms Application

Question

Background: I am working on a project that involves a WinForms app. The client wants to expose a local-only HTTP server to allow other apps to trigger functionality on a running instance of the WinForms app via a REST API (or similar). The preference is to implement the aforementioned API using ASP.NET Core.

My question is thus: How do I structure a project to have both an ASP.NET Core API and a WinForms GUI in the same process? Are there any pitfalls I'd have to be wary of?

Answer 1

Hosting ASP.NET CORE API in a Windows Forms Application and Interaction with Form

Here is a basic step by step example about how to create a project to host ASP.NET CORE API inside a Windows Forms Application and perform some interaction with Form.

To do so, follow these steps:

1. Create a Windows Forms Application name it MyWinFormsApp

2. Open Form1 in design mode and drop a TextBox on it.

3. Change the Modifiers property of the textBox1 in designer to Public and save it.

4. Install Microsoft.AspNetCore.Mvc package

5. Install Microsoft.AspNetCore package

6. Create a Startup.cs file in the root of the project, and copy the following code:

    using Microsoft.AspNetCore.Builder;
    using Microsoft.AspNetCore.Hosting;
    using Microsoft.AspNetCore.Mvc;
    using Microsoft.Extensions.Configuration;
    using Microsoft.Extensions.DependencyInjection;
    namespace MyWinFormsApp
    {
        public class Startup
        {
            public Startup(IConfiguration configuration)
            {
                Configuration = configuration;
            }
            public IConfiguration Configuration { get; }
            public void ConfigureServices(IServiceCollection services)
            {
                services.AddMvc().SetCompatibilityVersion(CompatibilityVersion.Version_2_2);
            }
            public void Configure(IApplicationBuilder app, IHostingEnvironment env)
            {
                if (env.IsDevelopment())
                {
                    app.UseDeveloperExceptionPage();
                }
                app.UseMvc();
            }
        }
    }
   

7. Copy the following code in Program.cs:

    using System;
    using System.Threading;
    using System.Windows.Forms;
    using Microsoft.AspNetCore;
    using Microsoft.AspNetCore.Hosting;
   
    namespace MyWinFormsApp
    {
        public class Program
        {
            public static Form1 MainForm { get; private set; }
   
            [STAThread]
            public static void Main(string[] args)
            {
                CreateWebHostBuilder(args).Build().RunAsync();
   
                Application.EnableVisualStyles();
                Application.SetCompatibleTextRenderingDefault(false);
                MainForm = new Form1();
                Application.Run(MainForm);
            }
   
            public static IWebHostBuilder CreateWebHostBuilder(string[] args) =>
                WebHost.CreateDefaultBuilder(args)
                    .UseStartup<Startup>();
        }
    }
   

8. Create a folder called Controllers in the root of the project.

9. Create ValuesController.cs in the Controllers folder and copy the following code to file:

    using System;
    using Microsoft.AspNetCore.Mvc;
   
    namespace MyWinFormsApp.Controllers
    {
        [Route("api/[controller]")]
        [ApiController]
        public class ValuesController : ControllerBase
        {
            [HttpGet]
            public ActionResult<string> Get()
            {
                string text = "";
                Program.MainForm.Invoke(new Action(() =>
                {
                    text = Program.MainForm.textBox1.Text;
                }));
                return text;
            }
   
            [HttpGet("{id}")]
            public ActionResult Get(string id)
            {
                Program.MainForm.Invoke(new Action(() =>
                {
                    Program.MainForm.textBox1.Text = id;
                }));
                return Ok();
            }
        }
    }
   

10. Run the application.

11. Type "hi" in the textBox1

12. Open browser and browse http://localhost:5000/api/values → You will see hi as response.

13. http://localhost:5000/api/values/bye → You will see bye in textBox1

Further Reading

You may also be interested in How to use Dependency Injection (DI) in Windows Forms (WinForms)

Answer 2

I Install Microsoft.AspNetCore.Mvc and Microsoft.AspNetCore package can't use

I look at this WebApplication.CreateBuilder Method Doc find need Microsoft.AspNetCore.dll, but I can't use this.

I hope it helps others.

---

Install Microsoft.AspNetCore.App package

dotnet add package Microsoft.AspNetCore.App --version 2.2.8

the Minimal API:

Microsoft.AspNetCore.Builder.WebApplication app = Microsoft.AspNetCore.Builder.WebApplication.Create(new string[] { });
app.MapGet("/", () => "Hello World!");
app.RunAsync();

Ok, now you can open http:localhost:5000 to look Hello World!

Because few people will use parameters in WinForm, string[] args is omitted here, and new string[] { } is used instead

---

If you want to ues controller, like ASP.NET Core, then you can use this:

var builder = Microsoft.AspNetCore.Builder.WebApplication.CreateBuilder(new string[]{});
builder.Services.AddControllers();

var app = builder.Build();
app.MapControllers();
app.RunAsync();

HomeController.cs

using Microsoft.AspNetCore.Mvc;

namespace RuyutWinFormsApi;

[Route("api/[controller]")]
[ApiController]
public class HomeController : ControllerBase
{
    [HttpGet]
    public IActionResult Get()
    {
        return Ok("This is a test api");
    }
}

you can open http://localhost:5000/api/home to look This is a test api

BTY, if you want to change port, you can add this:

app.Urls.Add("http://0.0.0.0:8080");

Answer 3

I have a class I made to do this. Basically I created a function in the .NET 6.0 Web API Controller starting template.

public async Task Listen(IServiceCollection services, List<Type> controllers, int port, CancellationToken token)
{
    var builder = WebApplication.CreateBuilder();
    builder.WebHost.ConfigureKestrel(options => options.Listen(System.Net.IPAddress.Parse("127.0.0.1"), port));
    // Add services to the container.

    builder.Services.AddControllers();
    // Learn more about configuring Swagger/OpenAPI at https://aka.ms/aspnetcore/swashbuckle
    builder.Services.AddEndpointsApiExplorer();
    builder.Services.AddSwaggerGen();

    builder.Services.Add(services);
    //builder.Services.AddSingleton<HostedCheckoutService>(hc);

    // Add our external card processor controller. This mocks a web page that is returned
    // in the Hosted Checkout iframe.
    //var assembly = typeof(LocalCardProcessorController).Assembly;
    foreach (var controller in controllers)
    {
        var assembly = controller.Assembly;
        builder.Services.AddControllers().PartManager.ApplicationParts.Add(new Microsoft.AspNetCore.Mvc.ApplicationParts.AssemblyPart(assembly));
    }

    var app = builder.Build();

    //Configure the HTTP request pipeline.
    if (true)//app.Environment.IsDevelopment())
    {
        // Need to manually navigate to http://127.0.0.1:16600/swagger/index.html
        app.UseDeveloperExceptionPage();
        app.UseSwagger();
        app.UseSwaggerUI(c => c.SwaggerEndpoint("v1/swagger.json", "MyAPI V1"));
    }

    app.UseHttpsRedirection();
    app.UseRouting();
    app.UseAuthorization();
    app.UseEndpoints(endpoints => endpoints.MapControllers());
           
    await app.RunAsync(token);
    await app.DisposeAsync();

}

Call it in your form like so;

APIServer server = new APIServer();

var serviceCollection = new ServiceCollection();
serviceCollection.AddSingleton<SomeService1>();
serviceCollection.AddSingleton<SomeService2>();
server.Listen(serviceCollection, new() { typeof(SomeController1), typeof(SomeController2) }, 9001, new CancellationToken());

Note Swagger is using Swashbuckle.AspNetCore (6.3.0)