Access to configuration without dependency injection

Wow, what a lot of comments, why don't people answer the question instead of telling someone they don't want to do what they obviously do. Anyway, hopefully this will keep both camps satisfied.

If you take a standard AppSettings class with a single public constructor that takes an IConfiguration that can be used to populate all the AppSettings properties, this keeps the ability for Dependency Injection.

If at the end of the constructor we set a static property 'Current' pointing to the current instance of AppSettings, this will allow us access to the settings from that point onwards via the static property without the need for further injection.

If we now create a static Default 'GetCurrentSettings' method to get the settings from a json file, this can be used as a default instantiation, so that if 'Current' is called and is set to null, we just go off and populate the settings from the file. Here's an example of what I mean...

public class AppSettings
{
    private static AppSettings _appSettings;

    public string AppConnection { get; set; }

    public AppSettings(IConfiguration config)
    {
        this.AppConnection = config.GetValue<string>("AppConnection");

        // Now set Current
        _appSettings = this;
    }

    public static AppSettings Current
    {
        get
        {
            if(_appSettings == null)
            {
                _appSettings = GetCurrentSettings();
            }

            return _appSettings;
        }
    }

    public static AppSettings GetCurrentSettings()
    {
        var builder = new ConfigurationBuilder()
                        .SetBasePath(Directory.GetCurrentDirectory())
                        .AddJsonFile("appsettings.json", optional: false, reloadOnChange: true)
                        .AddEnvironmentVariables();

        IConfigurationRoot configuration = builder.Build();

        var settings = new AppSettings(configuration.GetSection("AppSettings"));

        return settings;
    }
}

So from this you would be able to call anywhere in code AppSettings.Current.AppConnection

If it's been instantiated using DI the injected version would be retrieved otherwise the default version would be taken from an appsettings.json file. I doubt it satisfies everyone and I'm not sure I've explained it very well, but hopefully it makes sense.

I just made the config property in Startup static:

public static IConfiguration Configuration { get; set; }

Now I can access it anywhere in the application with just Startup.Configuration.

I am totally agree with solution suggested by @Hoot but i have modified class little. i have modified class because i need to pass dynamic Key to fetch value for same..

Configuration Class :

public class ConfigHelper
    {

        private static ConfigHelper _appSettings;

        public string appSettingValue { get; set; }

        public static string AppSetting(string Key)
        {
          _appSettings = GetCurrentSettings(Key);
          return _appSettings.appSettingValue;
        }

        public ConfigHelper(IConfiguration config, string Key)
        {
            this.appSettingValue = config.GetValue<string>(Key);
        }

        public static ConfigHelper GetCurrentSettings(string Key)
        {
            var builder = new ConfigurationBuilder()
                            .SetBasePath(Directory.GetCurrentDirectory())
                            .AddJsonFile("appsettings.json", optional: false, reloadOnChange: true)
                            .AddEnvironmentVariables();

            IConfigurationRoot configuration = builder.Build();

            var settings = new ConfigHelper(configuration.GetSection("AppSettings"), Key);

            return settings;
        }
    }

Appsettings.Json Configuration:

 "AppSettings": {
    "WebApplicationUrl": "http://localhost:0000/",
    "ServiceUrl": "http://localhost:0000/",
    "CommonServiceUrl": "http://localhost:0000/"
  }

Calling Example:

string ServiceUrl = ConfigHelper.AppSetting("ServiceUrl");

So from now we are able to pass dynamic key.

I have modified @Ankit Mori answer to a better dynamic solution and with strongly typed properties too.

using System.IO;
using Microsoft.Extensions.Configuration;

public class AppSettings
{

    #region Methods

    public static string GetSettingValue(string MainKey, string SubKey)
    {
        return Configuration.GetSection(MainKey).GetValue<string>(SubKey);
    }

    #endregion

    #region Properties

    public static IConfigurationRoot _configuration;
    public static IConfigurationRoot Configuration
    {
        get
        {
            if (_configuration == null)
            {
                IConfigurationBuilder builder = new ConfigurationBuilder()
                        .SetBasePath(Directory.GetCurrentDirectory())
                        .AddJsonFile("appsettings.json", optional: false, reloadOnChange: true)
                        .AddEnvironmentVariables();
                _configuration = builder.Build();
            }
            return _configuration;
        }
    }
    public static string MainAPI
    {
        get
        {
            return Configuration.GetSection("AppSettings").GetValue<string>("AppConnection");
        }
    }

    #endregion

}

You can try a utility method like so:

private static T? GetServiceInstance<T>(IServiceCollection services) where T : class
{
    return (T?)services.Where(s => s.ImplementationInstance is T)
        .Select(s => s.ImplementationInstance)
        .FirstOrDefault();
}

Then call it like like so:

var configuration = GetServiceInstance<IConfiguration>()