public class LanguageRouteConstraint : IRouteConstraint
    {
        public bool Match(HttpContext httpContext, IRouter route, string routeKey, RouteValueDictionary values, RouteDirection routeDirection)
        {
            if (!values.ContainsKey("lang"))
            {
                return false;
            }
            var lang = values["lang"].ToString();
            var result = lang == "fa" || lang == "en";
            return result;
        }
    }  

public void ConfigureServices(IServiceCollection services)
        {
            services.AddLocalization(o => o.ResourcesPath = "Resources");
            services.Configure<RouteOptions>(options =>
            {
                options.ConstraintMap.Add("lang", typeof(LanguageRouteConstraint));
            });

            services.AddMvc()
                .SetCompatibilityVersion(CompatibilityVersion.Version_2_2)
                .AddViewLocalization(LanguageViewLocationExpanderFormat.Suffix)
                .AddDataAnnotationsLocalization();

        public void Configure(IApplicationBuilder app, IHostingEnvironment env)
        {
            
            app.UseRequestLocalization(new RequestLocalizationOptions
            {
                DefaultRequestCulture = new RequestCulture(new CultureInfo("fa-IR")),
                SupportedCultures = new[]
                {
                    new CultureInfo("en-US"),
                    new CultureInfo("fa-IR"),
                },
                SupportedUICultures = new[]
                {
                    new CultureInfo("en-US"),
                    new CultureInfo("fa-IR"),
                },
                RequestCultureProviders = new List<IRequestCultureProvider>()
                {
                    new RouteDataRequestCultureProvider()
                    {
                        UIRouteDataStringKey = "lang",
                        RouteDataStringKey = "lang"
                    }
                }
            });

            app.UseMvc(routes =>
            {
                routes.MapRoute(
                    name: "LocalizedAreas",
                    template: "{lang:lang}/{area:exists}/{controller=Home}/{action=Index}/{id?}");

                routes.MapRoute(
                    name: "LocalizedDefault",
                    template: "{lang:lang}/{controller=Home}/{action=Index}/{id?}"
                );
                routes.MapRoute(
                    name: "default",
                    template: "{*catchall}",
                    defaults: new { controller = "Home", action = "RedirectToDefaultLanguage" });
            });

public class Startup 
{ 
   public Startup(IConfiguration configuration) 
   { 
       Configuration = configuration; 
   }

namespace FirstProjectServices
{
    public interface IMessagesService
    {
        string GetSiteName();
    }

    public class MessagesService : IMessagesService
    {
        public string GetSiteName()
        {
            return "DNT";
        }
    }
}

namespace FirstProjectServices
{
    public interface IMessagesService2
    {
        string GetSiteName();
    }

    public class MessagesService2 : IMessagesService2
    {
        public string GetSiteName()
        {
            return "DNT";
        }
    }
}

public class Startup
    {
       public void ConfigureServices(IServiceCollection services)
        {
            var collection = new ServiceCollection();

            services.Scan(scan => scan
                // We start out with all types in the assembly of ITransientService
                .FromAssemblyOf<IMessagesService>()
                .AddClasses(classes => classes.AssignableTo<MessagesService>())
                .AsImplementedInterfaces()
                .WithTransientLifetime()
               );

         }

       
        public void Configure(IApplicationBuilder app, IHostingEnvironment env, IMessagesService2 _messagesService)
        {
            if (env.IsDevelopment())
            {
                app.UseDeveloperExceptionPage();
            }

            // app.UseDefaultFiles();
            // app.UseStaticFiles();

            app.Run(async (context) =>
            {
                string siteName = _messagesService.GetSiteName();
                await context.Response.WriteAsync($"Site Name {siteName}");
            });
        }
    }

IF (currentYear<2023){
alert('Wear a mask!');
}

var showCoronaAlert=_cofiguration.GetValue<bool>("Features:showCoronaAlert"); // or read this from Database
If(showCoronaAlert){
alert(Wear a amask!);
}

Install-Package Microsoft.FeatureManagement

using Microsoft.FeatureManagement;
public void ConfigureServices(IServiceCollection services)
{
    services.AddFeatureManagement();
}

"FeatureManagement": {
   
}

 public class HomeController : Controller
    {
        private readonly IFeatureManager _featureManager;

        public HomeController(IFeatureManager featureManager)
        {
            _featureManager = featureManager;
        }
        public async Task<IActionResult> Index()
        {
            if(await _featureManager.IsEnabledAsync("MaskAlert"))
            {
                // show messeage
            }

            return View();
        }
    }

 "FeatureManagement": {
    "EmergencyBanner": {
      "EnabledFor": [
        {
          "Name": "Microsoft.TimeWindow",
          "Parameters": {
            "Start": "01 Mar 2021 12:00:00 +00:00",
            "End": "01 Apr 2021 12:00:00 +00:00"
          }
        }
      ]
    }
  }

if(await _featureManager.IsEnabledAsync("EmergencyBanner")){
// show Emergency banner 
}

"FeatureManagement": {
    "EmergencyBanner": {
      "EnabledFor": [
        {
          "Name": "Microsoft.TimeWindow",
          "Parameters": {
            "End": "01 Apr 2021 12:00:00 +00:00"
          }
        }
      ]
    }
  }

"FeatureManagement": {
    "ChatV2": {
      "EnabledFor": [
        {
          "Name": "BrowserFilter",
          "Parameters": {
            "AllowedBrowsers": [ "Chrome" ]
          }
        }
      ]
    }
  }

  public class BrowserFilterSettings
    {
        public string[] AllowedBrowsers { get; set; }
    }

public void ConfigureServices(IServiceCollection services)
        {
            services.TryAddSingleton<IHttpContextAccessor, HttpContextAccessor>();
            services.AddFeatureManagement()
                .AddFeatureFilter<BrowserFilter>();
        }

if(await _featureManager.IsEnabledAsync("ChatV2")){
// do something 
}

pm> Install-Package Swashbuckle.AspNetCore

http://localhost:port/swagger

Layout 00:46:16 
C# Metro applications have access to numerous XAML layout features. 
This module describes those services, and shows how to use them to support Windows 8 features such as display orientation, and snap. 

Introduction
Layout System
Size Properties
Alignment
Margin
Demo: Margin and Alignment 
Padding 
Panels 
Demo: Canvas 
Demo: Grid and Snap 
Data-Oriented Panels 
ScrollViewer 
Metro Layout Conventions 
Layout Change Events 
Summary