There was a console .NET Core 3.1 application for SOAP communication based on IHost / IHostBuilder.

New requirements came and I had to convert the application to the GUI application. I chose WinForms.

I made following changes in the CSPROJ file for that:

<Project .........>
  ...........
  <PropertyGroup>
    <ApplicationIcon />
    <OutputType>WinExe</OutputType>
    <UseWindowsForms>true</UseWindowsForms>
    <StartupObject />
  </PropertyGroup>
  ...........
</Project>

and in the Program.cs file:

using System.Windows.Forms;

.....................

   public static void Main(string[] args)
   {
     Application.EnableVisualStyles();
     Application.SetCompatibleTextRenderingDefault(false);
     ...................
     MainForm mainForm = new MainForm();
     loggerFactory.AddGUILogger(mainForm);
     ...................
       webBuilder.ConfigureServices(services =>
         services.TryAddSingleton(mainForm)
       );
     ...................
     IHost host = ............
     ...................
     host.RunAsync(); // host.Run();
     Application.Run(mainForm);
   }

It was Ok. The application was running with te main form, but while debugging it had two windows: the main form and the console window. When I closed the main form, the application stopped with an exception.

After some time I decided to change that and compared a newly created .NET Core 3.1 WinForms application with my application.

The main change was in project SDK. So I changed in the CSPROJ file

<Project Sdk="Microsoft.NET.Sdk.Web">

to

<Project Sdk="Microsoft.NET.Sdk.WindowsDesktop">

The other change was the [STAThread] attribute before the Main method.

Since then there is no additional console windows while debugging, but there is another problem: configuration is not being loaded from the appsettings.json file.

I have a configuration object and it initializes itself as follows:

public class Configuration
{
  private IConfigurationRoot _config = null;
  private IConfigurationRoot Config
  {
    get
    {
      if (_config == null)
      {
        string env = Environment.GetEnvironmentVariable("ASPNETCORE_ENVIRONMENT");
        IConfigurationBuilder builder = new ConfigurationBuilder()
            .AddJsonFile($"appsettings.json", true, true)
            .AddJsonFile($"appsettings{env}.json", true, true)
            .AddEnvironmentVariables();
        _config = builder.Build();
      }
    }
    return _config;
  }
}

Now when I request Config[paramName], I get always null.

How to make te configuration to work as it previously did?