public class DelegateCmd : ICommand, IDisposable
{
    private readonly Action<object?> execute;
    private readonly Func<object?, bool> canExecute;
    private bool isDisposed = false;
    public DelegateCmd(Action<object?> executeValue, Func<object?, bool> canExecuteValue=null)
    {
        execute = executeValue ?? throw new ArgumentNullException(nameof(executeValue));
        canExecute = canExecuteValue;
    }

    public event EventHandler? CanExecuteChanged;

    public bool CanExecute(object? parameter)
    {
        return canExecute == null ? true : canExecute(parameter);
    }

    public void Execute(object? parameter)
    {
        var handler = execute;
        handler?.Invoke(parameter);
    }

    public void RaiseCanExecuteChanged()
    {
        var handler = Volatile.Read(ref CanExecuteChanged);
        if(handler==null)
        {
            return;
        }

        if (Application.Current?.Dispatcher?.CheckAccess() == true)
        {
            handler?.Invoke(this, EventArgs.Empty);
        }
        else
        {
            Application.Current?.Dispatcher.Invoke(() =>
            {
                handler?.Invoke(this, EventArgs.Empty);
            });
        }
    }

    public void Dispose()
    {
        if(isDisposed)
        {
            return;
        }
        GC.SuppressFinalize(this);
        Dispose(true);
    }

    private void Dispose(bool isDisposing)
    {
        if(!isDisposing)
        {
            return;
        }

        var eventHandler = Volatile.Read(ref CanExecuteChanged);
        if(eventHandler!=null)
        {
            foreach(var del in eventHandler.GetInvocationList())
            {
                CanExecuteChanged -= (EventHandler)del;
            }
        }
        isDisposed = true;
    }
}

<Window x:Class="WpfApp11.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
        xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
        xmlns:local="clr-namespace:WpfApp11"
        mc:Ignorable="d"
        Title="{Binding MainTitle}"
        WindowState="Maximized">
    <Window.DataContext>
        <local:MainVM/>
    </Window.DataContext>
    <Grid>
        <DataGrid ItemsSource="{Binding BooksCollection}"
                  VirtualizingPanel.IsVirtualizing="True"
                  VirtualizingPanel.VirtualizationMode="Recycling"
                  VirtualizingPanel.CacheLengthUnit="Item"
                  VirtualizingPanel.CacheLength="5,5"
                  ScrollViewer.CanContentScroll="True"
                  ScrollViewer.IsDeferredScrollingEnabled="True"
                  AutoGenerateColumns="True"
                  CanUserAddRows="False"
                  UseLayoutRounding="True"
                  SnapsToDevicePixels="True"
                  SelectionMode="Extended">
            <DataGrid.Resources>
                <Style TargetType="DataGridRow">
                    <Setter Property="FontSize" Value="30"/>
                    <Style.Triggers>
                        <Trigger Property="IsMouseOver" Value="True">
                            <Setter Property="FontSize" Value="40"/>
                            <Setter Property="Foreground" Value="Red"/>
                        </Trigger>
                    </Style.Triggers>
                </Style>
            </DataGrid.Resources>
            <DataGrid.ContextMenu>
                <ContextMenu>
                    <MenuItem Header="Save As Json"
                              Command="{Binding SaveAsJsonCmd}"
                              CommandParameter="{Binding RelativeSource={RelativeSource AncestorType=ContextMenu},Path=PlacementTarget.SelectedItems}"/>
                </ContextMenu>
            </DataGrid.ContextMenu>
        </DataGrid>
    </Grid>
</Window>


using System.Collections.ObjectModel;
using System.ComponentModel;
using System.Diagnostics;
using System.Net.Http;
using System.Runtime.CompilerServices;
using System.Text;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Data;
using System.Windows.Documents;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Media.Imaging;
using System.Windows.Navigation;
using System.Windows.Shapes;
using System.Windows.Threading;
using Newtonsoft.Json;

namespace WpfApp11
{
    /// <summary>
    /// Interaction logic for MainWindow.xaml
    /// </summary>
    public partial class MainWindow : Window
    {
        public MainWindow()
        {
            InitializeComponent();
        }
    }

    public class MainVM : INotifyPropertyChanged
    {
        private readonly HttpClient client = new HttpClient();
        private readonly object isLoadingLock = new object();
        private string originalUrl = "http://localhost:62889/BookService.svc/getbookslist?cnt=";
        public DelegateCmd SaveAsJsonCmd { get; set; }
        public MainVM()
        {
            if(DesignerProperties.GetIsInDesignMode(new DependencyObject()))
            {
                return;
            }
            SaveAsJsonCmd = new DelegateCmd(SaveAsJsonCmdExecuted);

            Task.Run(async () =>
            {
                
                while (true)
                {
                    await InitBooksAsync();
                    await Task.Delay(10000);
                }
            });
        }

        private void SaveAsJsonCmdExecuted(object? obj)
        {
            var items = ((System.Collections.IList)obj)?.Cast<Book>()?.ToList();
        }

        private async Task InitBooksAsync(int cnt=1000000)
        {
            if(IsLoading)
            {
                return;
            }
            IsLoading = true;

            Application.Current?.Dispatcher.Invoke(() =>
            {
                MainTitle = $"{DateTime.Now},loading...";
            });
            try
            {
                string requestUrl = $"{originalUrl}{cnt}";
                
                await Task.Run(async() =>
                {
                    string jsonStr = await client.GetStringAsync(requestUrl);
                    Application.Current?.Dispatcher?.InvokeAsync(() =>
                    {
                        BooksCollection = new ObservableCollection<Book>(JsonConvert.DeserializeObject<List<Book>>(jsonStr));
                        MainTitle = $"{DateTime.Now},loaded FirstId:{BooksCollection?.FirstOrDefault().Id}," +
                        $"LastId:{BooksCollection?.LastOrDefault()?.Id}";
                    },DispatcherPriority.Background);
                });                 
            }
            catch (Exception ex)
            {
                PrintMsg(ex?.Message);
            }
            finally
            {
                IsLoading = false;
            }
        }

        

        private void PrintMsg(string msg=null)
        {
#if DEBUG
            System.Diagnostics.Debug.WriteLine($"{DateTime.Now},{msg}");
#else
            System.Diagnostics.Trace.WriteLine($"{DateTime.Now},{msg}");
#endif
        }

        private string mainTitle=$"{DateTime.Now}";
        public string MainTitle
        {
            get
            {
                return mainTitle;
            }
            set
            {
                if(value!=mainTitle)
                {
                    mainTitle = value;
                    OnPropertyChanged();
                    PrintMsg(MainTitle);
                }
            }
        }

        private bool isLoading;
        public bool IsLoading
        {
            get
            {
                lock(isLoadingLock)
                {
                    return isLoading;
                }
            }
            set
            {
                lock(isLoadingLock)
                {
                    if(value!=isLoading)
                    {
                        isLoading = value;
                        OnPropertyChanged();
                    }
                }
            }
        }

        private ObservableCollection<Book> booksCollection;
        public ObservableCollection<Book> BooksCollection
        {
            get
            {
                return booksCollection;
            }
            set
            {
                if(value!=booksCollection)
                {
                    booksCollection = value;
                    OnPropertyChanged();
                }
            }
        }

        public event PropertyChangedEventHandler? PropertyChanged;
        private void OnPropertyChanged([CallerMemberName]string propertyName="")
        {
            var handler=Volatile.Read(ref PropertyChanged);
            if(handler==null)
            {
                return;
            }
            handler?.Invoke(this, new PropertyChangedEventArgs(propertyName));
        }
    }

    public class Book
    {
        public long Id { get; set; }
        public string Name { get; set; }
        public string ISBN { get; set; }
        public string Abstract { get; set; }
        public string Author { get; set; }
        public string Comment { get; set; }
        public string Content { get; set; }
        public string Summary { get; set; }
        public string Title { get; set; }
        public string Topic { get; set; }
    }

    public class DelegateCmd : ICommand, IDisposable
    {
        private readonly Action<object?> execute;
        private readonly Func<object?, bool> canExecute;
        private bool isDisposed = false;
        public DelegateCmd(Action<object?> executeValue, Func<object?, bool> canExecuteValue=null)
        {
            execute = executeValue ?? throw new ArgumentNullException(nameof(executeValue));
            canExecute = canExecuteValue;
        }

        public event EventHandler? CanExecuteChanged;

        public bool CanExecute(object? parameter)
        {
            return canExecute == null ? true : canExecute(parameter);
        }

        public void Execute(object? parameter)
        {
            var handler = execute;
            handler?.Invoke(parameter);
        }

        public void RaiseCanExecuteChanged()
        {
            var handler = Volatile.Read(ref CanExecuteChanged);
            if(handler==null)
            {
                return;
            }

            if (Application.Current?.Dispatcher?.CheckAccess() == true)
            {
                handler?.Invoke(this, EventArgs.Empty);
            }
            else
            {
                Application.Current?.Dispatcher.Invoke(() =>
                {
                    handler?.Invoke(this, EventArgs.Empty);
                });
            }
        }

        public void Dispose()
        {
            if(isDisposed)
            {
                return;
            }
            GC.SuppressFinalize(this);
            Dispose(true);
        }

        private void Dispose(bool isDisposing)
        {
            if(!isDisposing)
            {
                return;
            }

            var eventHandler = Volatile.Read(ref CanExecuteChanged);
            if(eventHandler!=null)
            {
                foreach(var del in eventHandler.GetInvocationList())
                {
                    CanExecuteChanged -= (EventHandler)del;
                }
            }
            isDisposed = true;
        }
    }
}

//using System;
using System.Collections.Generic;
using System.Linq;
using System.Runtime.Serialization;
using System.ServiceModel;
using System.ServiceModel.Web;
using System.Text;

namespace WcfService4
{
    // NOTE: You can use the "Rename" command on the "Refactor" menu to change the interface name "IBookService" in both code and config file together.
    [ServiceContract]
    public interface IBookService
    {
        [OperationContract]
        [WebGet(UriTemplate ="/getbookslist?cnt={cnt}",RequestFormat =WebMessageFormat.Json,
            ResponseFormat = WebMessageFormat.Json)]
        List<Book> GetBooksList(int cnt);
    }

    public class Book
    {
        public long Id { get; set; }
        public string Name { get; set; }
        public string ISBN { get; set; }
        public string Abstract {  get; set; }
        public string Author { get; set;  }
        public string Comment {  get; set; }
        public string Content { get; set;  }
        public string Summary {  get; set; }
        public string Title { get; set; }
        public string Topic { get; set; }
    }
}


//using System;
using System.Collections.Generic;
using System.Linq;
using System.Runtime.Serialization;
using System.ServiceModel;
using System.Text;
using System.Threading;

namespace WcfService4
{
    // NOTE: You can use the "Rename" command on the "Refactor" menu to change the class name "BookService" in code, svc and config file together.
    // NOTE: In order to launch WCF Test Client for testing this service, please select BookService.svc or BookService.svc.cs at the Solution Explorer and start debugging.
    public class BookService : IBookService
    {
        private static long idx = 1;
        private static (long, long) GetStartEnd(int cnt)
        {
            long end = Interlocked.Add(ref idx, cnt);
            long start = end - cnt;
            return (start, end);
        }
        public List<Book> GetBooksList(int cnt)
        {
            var (start, end) = GetStartEnd(cnt);
            List<Book> bksList = new List<Book>(cnt);
            for(long i=start;i<end;i++)
            {
                bksList.Add(new Book()
                {
                    Id = i,
                    Name = $"Name_{i}",
                    ISBN = $"ISBN_{i}_{Guid.NewGuid():N}",
                    Abstract = $"Abstract_{i}",
                    Author=$"Author_{i}",
                    Comment=$"Comment_{i}",
                    Content=$"Content_{i}",
                    Summary=$"Summary_{i}",
                    Title=$"Title_{i}",
                    Topic=$"Topic_{i}"
                });
            }
            return bksList;
        }
    }
}

//<?xml version="1.0"?>
<configuration>

  <appSettings>
    <add key="aspnet:UseTaskFriendlySynchronizationContext" value="true" />
  </appSettings>
  <system.web>
    <compilation debug="true" targetFramework="4.8" />
    <httpRuntime targetFramework="4.8"/>
  </system.web>
  <system.serviceModel>
      <bindings>
          <webHttpBinding>
              <binding name="BookServiceWebHttpBinding"
                        openTimeout="01:00:00"
                        closeTimeout="01:00:00"
                        sendTimeout="01:00:00"
                        receiveTimeout="01:00:00"
                        maxBufferPoolSize="2147483647"
                        maxBufferSize="2147483647"
                        maxReceivedMessageSize="2147483647"
                        transferMode="Buffered">
                  <readerQuotas maxArrayLength="2147483647"
                                maxBytesPerRead="2147483647"
                                maxDepth="2147483647"
                                maxNameTableCharCount="2147483647"
                                maxStringContentLength="2147483647"/>
                  <security mode="None"/>
              </binding>
          </webHttpBinding>
      </bindings>
    <behaviors>
      <serviceBehaviors>
        <behavior name="BookServiceBehavior">
          <!-- To avoid disclosing metadata information, set the values below to false before deployment -->
          <serviceMetadata httpGetEnabled="true" httpsGetEnabled="true"/>
          <!-- To receive exception details in faults for debugging purposes, set the value below to true.  Set to false before deployment to avoid disclosing exception information -->
          <serviceDebug includeExceptionDetailInFaults="false"/>
        </behavior>
      </serviceBehaviors>
        <endpointBehaviors>
            <behavior name="BookServiceEndPointBehavior">
                <webHttp/>
            </behavior>
        </endpointBehaviors>
    </behaviors>
    <protocolMapping>
        <add binding="basicHttpsBinding" scheme="https" />
    </protocolMapping>    
    <serviceHostingEnvironment aspNetCompatibilityEnabled="true" multipleSiteBindingsEnabled="true" />
  <services>
      <service name="WcfService4.BookService" 
               behaviorConfiguration="BookServiceBehavior">
          <endpoint address=""
                    binding="webHttpBinding"
                    contract="WcfService4.IBookService"
                    bindingConfiguration="BookServiceWebHttpBinding"
                    behaviorConfiguration="BookServiceEndPointBehavior"/>
      </service>
  </services>
  </system.serviceModel>
  <system.webServer>
    <modules runAllManagedModulesForAllRequests="true"/>
    <!--
        To browse web app root directory during debugging, set the value below to true.
        Set to false before deployment to avoid disclosing web app folder information.
      -->
    <directoryBrowse enabled="true"/>
  </system.webServer>

</configuration>