public class OnlineUserMiddleWare
    {
        private readonly RequestDelegate _next;
        private readonly IMemoryCache _memoryCache;

        public OnlineUserMiddleWare(RequestDelegate next, IMemoryCache memoryCache)
        {
            _next = next;
            _memoryCache = memoryCache;
        }

        public async Task Invoke(HttpContext context)
        {
            if (!_memoryCache.TryGetValue("OnlineUsers", out Dictionary<string,DateTime> onlineUsers))
            {
                onlineUsers = new Dictionary<string, DateTime>();
                _memoryCache.Set("OnlineUsers", onlineUsers);
            }
            if (context.User.Identity.IsAuthenticated)
            {
                var name = context.User.Identity.Name;
                if (name != null)
                {
                    if (onlineUsers.ContainsKey(name))
                        onlineUsers[name] = DateTime.Now;
                    else
                        onlineUsers.Add(name, DateTime.Now);
                }

            }

           
                foreach (var online in onlineUsers)
                {
                    if (online.Value < DateTime.Now.AddMinutes(-10))
                        onlineUsers.Remove(online.Key);
                }
           
            await _next(context);
        }

        
    }

 public void Configure(IApplicationBuilder app, IWebHostEnvironment env, IServiceProvider serviceProvider)
        {
         ...
            app.UseMiddleware<OnlineUserMiddleWare>();
         ...
        }

public class DashboardController 
    {
        private readonly IMemoryCache _memoryCache;
        public DashboardController(memoryCache)
        {
            _memoryCache = memoryCache;
        }
        public IActionResult Index()
        {
         
            _memoryCache.TryGetValue("OnlineUsers", out Dictionary<string, DateTime> onlineUsers);
            ViewBag.OnlineUsers = onlineUsers.Count;
            return View();
        }       
    }

           if(context.Request.Path.StartsWithSegments("/Identity/Account/Login"))
            {
                foreach (var online in onlineUsers)
                {
                    if (online.Value < DateTime.Now.AddMinutes(-10))
                        onlineUsers.Remove(online.Key);
                }
            }

    public async Task<IEnumerable<UserDto>> GetUsersInParallelInWithBatches(IEnumerable<int> userIds)
    {
        var tasks = new List<Task<IEnumerable<UserDto>>>();
        var batchSize = 100;
        int numberOfBatches = (int)Math.Ceiling((double)userIds.Count() / batchSize);

        for (int i = 0; i < numberOfBatches; i++)
        {
            var currentIds = userIds.Skip(i * batchSize).Take(batchSize);
            tasks.Add(client.GetUsers(currentIds));
        }
            
        return (await Task.WhenAll(tasks)).SelectMany(u => u);
    }

// Create dictionary and add five keys and values.
        var dictionary = new Dictionary<string, int>();
        dictionary.Add("car", 2);
        dictionary.Add("apple", 1);
        dictionary.Add("zebra", 0);
        dictionary.Add("mouse", 5);
        dictionary.Add("year", 3);

        // Acquire keys and sort them.
        var list = dictionary.Keys.ToList();
        list.Sort();

        // Loop through keys.
        foreach (var key in list)
        {
            Console.WriteLine("{0}: {1}", key, dictionary[key]);
        }

The settings

<appSettings>
    <add key="RetryAttempts" value="5" />
    <add key="ApplicationBuildDate" value="11/4/1999 6:23 AM" />
</appSettings>

The code

dynamic config = new Configuration();
var retryAttempts1 = config.RetryAttempts;                 // returns 5 as a string
var retryAttempts2 = config.RetryAttempts(10);             // returns 5 if found in config, else 10
var retryAttempts3 = config.RetryAttempts(userInput, 10);  // returns 5 if it exists in config, else userInput i

Car car = new("Test", "Blue");

var (model, color) = car;
// Initialization

string model = string.Empty;
string color = string.Empty;
(model, color) = car;
// Assignment

string model = string.Empty;
(model, var color) = car;
// Initialization and assignment

var viewEngineResult = _viewEngine.FindView(actionContext, viewNameOrPath, isMainPage: false);
            if (!viewEngineResult.Success)
            {
                viewEngineResult = _viewEngine.GetView("~/", viewNameOrPath, isMainPage: false);
                if (!viewEngineResult.Success)
                {
                    throw new FileNotFoundException($"Couldn't find '{viewNameOrPath}'");
                }
            }

            var view = viewEngineResult.View;

var view = CreateViewFromString(@"@model int <div class="AAA">@Model</div>");

public class SampleModel
{
public byte? Value { get; set; }
}

var options = new JsonSerializerOptions();
options.NumberHandling = System.Text.Json.Serialization.JsonNumberHandling.AllowReadingFromString;

var body = @"{""Value"":""""}";
var model = JsonSerializer.Deserialize<SampleModel>(body, options);

var items = (from p in context.Categories
                select new  
                {  
                    Id = p.Id,  
                    Name = p.Name,  
                    DateAdded = EF.Property<DateTime>(p, "DateAdded")  
                }).ToList();

var cList = context.Categories
        .OrderBy(b => EF.Property<DateTime>(b, "DateAdded")).ToList();
foreach (var cat in cList)
{
   Console.Write("Category Name: " + cat.CategoryName);
   Console.WriteLine(" Created: " + context.Entry(cat).Property("DateAdded").CurrentValue);
}

var serviceCollection = new ServiceCollection();
serviceCollection.AddDataProtection();
var services = serviceCollection.BuildServiceProvider();
var protectionProvider = ActivatorUtilities.CreateInstance<ProtectionProvider>(services);
string result = protectionProvider.Encrypt(Str);