Cannot add appsettings.json inside WPF project .net core 3.0

Steps:

• To Add the following nuget packages

    Microsoft.Extensions.Configuration
    Microsoft.Extensions.Configuration.FileExtensions
    Microsoft.Extensions.Configuration.Json
    Microsoft.Extensions.DependencyInjection
  

• You would need to create and add appsettings.json manually and set copy it to output directory as copy if newer

---

AppSetting.json

   {
  "ConnectionStrings": {
    "BloggingDatabase": "Server=(localdb)\\mssqllocaldb;Database=EFGetStarted.ConsoleApp.NewDb;Trusted_Connection=True;"
  },
}

Program.cs (For .NetCore Console App)

static void Main(string[] args)
{
    var builder = new ConfigurationBuilder()
        .SetBasePath(Directory.GetCurrentDirectory())
        .AddJsonFile("appsettings.json", optional: false, reloadOnChange: true);

    IConfigurationRoot configuration = builder.Build();

    Console.WriteLine(configuration.GetConnectionString("BloggingDatabase"));
}

App.xaml.cs (For .NET CORE WPF)

public partial class App : Application
{
    public IServiceProvider ServiceProvider { get; private set; }
 
    public IConfiguration Configuration { get; private set; }
 
    protected override void OnStartup(StartupEventArgs e)
    {
        var builder = new ConfigurationBuilder()
         .SetBasePath(Directory.GetCurrentDirectory())
         .AddJsonFile("appsettings.json", optional: false, reloadOnChange: true);
 
        Configuration = builder.Build();

      Console.WriteLine(Configuration.GetConnectionString("BloggingDatabase"));    

        var serviceCollection = new ServiceCollection();
        ConfigureServices(serviceCollection);
 
        ServiceProvider = serviceCollection.BuildServiceProvider();
 
        var mainWindow = ServiceProvider.GetRequiredService<MainWindow>();
        mainWindow.Show();
    }
 
    private void ConfigureServices(IServiceCollection services)
    {
        // ...
 
        services.AddTransient(typeof(MainWindow));
    }
}

---

References:

• https://blog.bitscry.com/2017/05/30/appsettings-json-in-net-core-console-app/
• https://marcominerva.wordpress.com/2019/03/06/using-net-core-3-0-dependency-injection-and-service-provider-with-wpf/
• https://docs.microsoft.com/en-us/ef/core/miscellaneous/connection-strings

It's no requirement to switch to an appsettings.json file in .NET Core. You may still use the very same "old" XML-based App.config file in a WPF app that targets .NET Core if you want to.

Just add a new configuration file (Project->Add New Item->Application Configuration File) to your project and name it "App.config". If you then add the following contents to it:

<?xml version="1.0" encoding="utf-8" ?>
<configuration>
   <connectionStrings>
    <add name="connectionString" connectionString="..."/>
  </connectionStrings>
</configuration>

...you should be able to get the connection string at runtime using the ConfigurationManager API:

ConfigurationManager.ConnectionStrings["connectionString"].ConnectionString;

The default WPF template should include the System.Configuration.ConfigurationManager package by default.