Creating Mobile Apps with Xamarin.Forms Book Preview 2 

import {Book} from "./testmd";

var numbers = new List<int> { -7, 1, 5, -6 };

var sortedNumbers1 = numbers.OrderBy(n => n);
var sortedNumbers2 = numbers.OrderByDescending(n => n);

public static IOrderedEnumerable<TSource> OrderBy<TSource,TKey>(
   [NotNull] this IEnumerable<TSource> source,
   [NotNull] Func<TSource,TKey> keySelector)

var sortedNumbers3 = numbers.Order();
var sortedNumbers4 = numbers.OrderDescending();

public static IOrderedEnumerable<T> Order<T>(this IEnumerable<T> source)
public static IOrderedEnumerable<T> OrderDescending<T>(this IEnumerable<T> source)

public class User
{
   public string Name { set; get; }
   public int Age { set; get; }
}

List<User> users = new()
                           {
                               new User { Name = "User 1", Age = 34 },
                               new User { Name = "User 2", Age = 24 },
                           };

var orderedUsers = users.Order();

public class User : IComparable<User>
{
    public string Name { set; get; }
    public int Age { set; get; }

    public int CompareTo(User? other)
    {
        if (ReferenceEquals(this, other))
        {
            return 0;
        }

        if (ReferenceEquals(null, other))
        {
            return 1;
        }

        var nameComparison = string.Compare(Name, other.Name, StringComparison.Ordinal);
        if (nameComparison != 0)
        {
            return nameComparison;
        }

        return Age.CompareTo(other.Age);
    }
}

var orderedUsers2 = users.OrderBy(user => user.Name).ThenBy(user => user.Age);

dotnet add package MongoDB.Driver

public class BaseModel
{
    public BaseModel()
    {
        CreationDate=DateTime.Now;
    }
    public string Id { get; set; }
    public DateTime CreationDate { get; set; }
    public bool IsRemoved { get; set; }
    public DateTime? ModificationDate { get; set; }

}

public class BaseModel
    {
        [BsonId]
        [BsonRepresentation((BsonType.ObjectId))]
        public string Id { get; set; }
    }

BsonClassMap.RegisterClassMap<BaseModel>(map =>
{
    map.SetIdMember(map.GetMemberMap(x=>x.Id));
    map.GetMemberMap(x => x.Id)
        .SetSerializer(new StringSerializer(BsonType.ObjectId));
});

public class Employee : BaseModel
{
    public string FirstName { get; set; }
    public string LastName { get; set; }
}
//=================
BsonClassMap.RegisterClassMap<Employee >(map =>
{
    map.SetIdMember(map.GetMemberMap(x=>x.Id));
    map.GetMemberMap(x => x.Id)
        .SetSerializer(new StringSerializer(BsonType.ObjectId));
});

  public interface IMongoDbContext
    {
        IMongoCollection<TEntity> GetCollection<TEntity>();
    }

  public class MongoDbContext : IMongoDbContext
    {

        private readonly IMongoClient _client;
        private readonly IMongoDatabase _database;

        public MongoDbContext(string databaseName,string connectionString)
        {
            var settings = MongoClientSettings.FromUrl(new MongoUrl(connectionString));
            _client = new MongoClient(settings);
            _database = _client.GetDatabase(databaseName);
        }

        public IMongoCollection<TEntity> GetCollection<TEntity>()
        {
            return _database.GetCollection<TEntity>(typeof(TEntity).Name.ToLower() + "s");
        }
    }

public static class MongoDbContextService
{
    public static void AddMongoDbContext(this IServiceCollection services,string databaseName,string connectionString)
    {
        services.AddSingleton<IMongoDbContext>(serviceProvider => new MongoDbContext(databaseName, connectionString));
    }
}

//===============
Program.cs

builder.Services.AddMongoDbContext("bookstore", "mongodb://localhost:27017");

public interface IRepository<T> where T : BaseModel
{

    IMongoCollection<T> GetCollection();
    IMongoQueryable<T> GetFilteredCollection();
}

public class Repository<T> : IRepository<T> where T:BaseModel
{
    private IMongoDbContext _mongoDbContext;

    public Repository(IMongoDbContext mongoDbContext)
    {
        _mongoDbContext = mongoDbContext;
    }

    public IMongoCollection<T> GetCollection()
    {
        return _mongoDbContext.GetCollection<T>();
    }
    
    public IMongoQueryable<T> GetFilteredCollection()
    {
        var query= _mongoDbContext.GetCollection<T>().AsQueryable();
        
        //================= Global Query Filters ====================
        
        //Filter 1
        query=query.Where(x => x.RemovedAt.HasValue == false);
        
        //==============================================================
        
        return query;
    }
}

public interface IRepository<T> where T : BaseModel
{

    IMongoCollection<T> GetCollection();
    IMongoQueryable<T> GetFilteredCollection();
}

public class Repository<T> : IRepository<T> where T:BaseModel
{
    private IMongoDbContext _mongoDbContext;

    public Repository(IMongoDbContext mongoDbContext)
    {
        _mongoDbContext = mongoDbContext;
    }

    public IMongoCollection<T> GetCollection()
    {
        return _mongoDbContext.GetCollection<T>();
    }
    
    public IMongoQueryable<T> GetFilteredCollection()
    {
        var query= _mongoDbContext.GetCollection<T>().AsQueryable();
        
        //================= Global Query Filters ====================
        
        //Filter 1
        query=query.Where(x => x.RemovedAt.HasValue == false);
        
        //==============================================================
        
        return query;
    }
}

  var ctx = new DynamicSlideShowEntities();
  var list = ctx.Pictures.ToList();
  string str = JsonConvert.SerializeObject(list);
  context.Response.Write(str);

<head runat="server">
    <title>Dynamic SlideShow</title>
    <link href="CSS/orbit-1.2.3.css" rel="stylesheet" type="text/css" />
    <script src="Script/jquery-1.7.1.min.js" type="text/javascript"></script>
    <script src="Script/jquery.orbit-1.2.3.min.js" type="text/javascript"></script>
    <script type="text/javascript">
        $(function () {
            $.ajax({
                url: "Handler.ashx",
                contentType: "application/json; charset=utf-8",
                success: function (data) {
                    $.each(data, function (i, b) {
                        var str = '<img src="' + b.PicturePath + '" alt="' + b.PictureText + '"/>';
                        $("#featured").append(str);
                    });
                    $('#featured').orbit();
                },
                dataType: "json"

            });
            });
    </script>
</head>
<body>
    <form id="form1" runat="server">
    <div id="featured">
    </div>
    </form>
</body>

<Window x:Class="Async10.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        Title="MainWindow" Height="350" Width="525">
    <DockPanel>
        <DockPanel Dock="Top">
            <Button Name="BtnGo" Content="Go" Click="BtnGo_OnClick" />
            <ProgressBar Name="ProgressBar" IsIndeterminate="True" Visibility="Collapsed"/>
        </DockPanel>
        <TextBox Name="Results"/>
    </DockPanel>
</Window>

using System.Net.Http;
using System.Windows;

namespace Async10
{
    public partial class MainWindow
    {
        public MainWindow()
        {
            InitializeComponent();
        }

        private void BtnGo_OnClick(object sender, RoutedEventArgs e)
        {
            BtnGo.IsEnabled = false;
            ProgressBar.Visibility = Visibility.Visible;

            var url = "https://www.dntips.ir";
            var client = new HttpClient(); // make sure you have an assembly reference to System.Net.Http.dll
            client.DefaultRequestHeaders.UserAgent.ParseAdd("Test Async");
            var task = client.GetStringAsync(url);
            task.ContinueWith(t =>
            {
                Results.Text = t.Result;

                BtnGo.IsEnabled = true;
                ProgressBar.Visibility = Visibility.Collapsed;
            });
        }
    }
}

 The calling thread cannot access this object because a different thread owns it.

 var context = SynchronizationContext.Current;
task.ContinueWith(t => context.Post(state =>
{
   Results.Text = t.Result;

   BtnGo.IsEnabled = true;
   ProgressBar.Visibility = Visibility.Collapsed;
}, null));

 var taskScheduler = TaskScheduler.FromCurrentSynchronizationContext();
task.ContinueWith(t =>
{
   Results.Text = t.Result;

   BtnGo.IsEnabled = true;
   ProgressBar.Visibility = Visibility.Collapsed;
}, taskScheduler);

 private async void BtnGo_OnClick(object sender, RoutedEventArgs e)

        private async void BtnGo_OnClick(object sender, RoutedEventArgs e)
        {
            BtnGo.IsEnabled = false;
            ProgressBar.Visibility = Visibility.Visible;

            var url = "https://www.dntips.ir";
            var client = new HttpClient(); // make sure you have an assembly reference to System.Net.Http.dll
            client.DefaultRequestHeaders.UserAgent.ParseAdd("Test Async");
            Results.Text = await client.GetStringAsync(url);
            BtnGo.IsEnabled = true;
            ProgressBar.Visibility = Visibility.Collapsed;
        }