.Net Core 2.0 appsettings with .net full framework using ConfigurationManager

Question

Assuming the following project structure:

1. Project A:

   • .net full framework ( 4.6.2)
   • internally accesses configuration via:

   ConfigurationManager.AppSettings["key"];

2. Project B:

   • .net core 2.0 ( compiling to .net 4.6.2)
   • references and uses project A

The Problem:
.net core uses the new configuration mechanism - is there a way to hook up the .net core config ( in project B) in a way that will enable project A to consume configuration via ConfigurationManager - i.e without code changes in project A ?

adding NuGet package System.Configuration.ConfigurationManager like in this answer only adds ConfigurationManager to project B but in project A no configuration is available via ConfigurationManager

Answer 1

Trick is to use ConfigurationManager.AppSettings.Set method to prepopulate ConfigurationManager.AppSettings from .NET Core so class libraries can use it later.

I am using following classes to add json settings into ConfigurationManager.

public class CustomJsonConfigurationProvider : JsonConfigurationProvider
{
    public CustomJsonConfigurationProvider(JsonConfigurationSource source) : base(source) { }

    public override void Load()
    {
        base.Load();
        foreach (string key in Data.Keys)
        {
            string[] keyParts = key.Split(new[] { ":" }, StringSplitOptions.RemoveEmptyEntries);
            ConfigurationManager.AppSettings.Set(keyParts[keyParts.Length - 1], Data[key]);
        }
    }
}

public class CustomJsonConfigurationSource : JsonConfigurationSource
{
    public override IConfigurationProvider Build(IConfigurationBuilder builder)
    {
        FileProvider = FileProvider ?? builder.GetFileProvider();
        return new CustomJsonConfigurationProvider(this);
    }
}

public static class CustomConfiguratorExtensions
{
    public static IConfigurationBuilder AddCustomJsonFile(this IConfigurationBuilder builder, string path)
    {
        return AddCustomJsonFile(builder, provider: null, path: path, optional: false, reloadOnChange: false);
    }

    public static IConfigurationBuilder AddCustomJsonFile(this IConfigurationBuilder builder, string path, bool optional)
    {
        return AddCustomJsonFile(builder, provider: null, path: path, optional: optional, reloadOnChange: false);
    }

    public static IConfigurationBuilder AddCustomJsonFile(this IConfigurationBuilder builder, string path, bool optional, bool reloadOnChange)
    {
        return AddCustomJsonFile(builder, provider: null, path: path, optional: optional, reloadOnChange: reloadOnChange);
    }

    public static IConfigurationBuilder AddCustomJsonFile(this IConfigurationBuilder builder, IFileProvider provider, string path, bool optional, bool reloadOnChange)
    {
        if (provider == null && Path.IsPathRooted(path))
        {
            provider = new PhysicalFileProvider(Path.GetDirectoryName(path));
            path = Path.GetFileName(path);
        }

        var source = new CustomJsonConfigurationSource
        {
            FileProvider = provider,
            Path = path,
            Optional = optional,
            ReloadOnChange = reloadOnChange
        };

        builder.Add(source);

        return builder;
    }
}

Usage:

builder.ConfigureAppConfiguration((w, c) =>
{
    c.AddCustomJsonFile("appsettings.json");
});