WPF usercontrol pass contextmenu command via implemented Freezable class which does not attach on Visual tree, then invoked in caller MVVM

public class ProxyBinding : Freezable
{
    protected override Freezable CreateInstanceCore()
    {
        return new ProxyBinding();
    }


    public object SourceObject
    {
        get { return (object)GetValue(SourceObjectProperty); }
        set { SetValue(SourceObjectProperty, value); }
    }

    // Using a DependencyProperty as the backing store for SourceObject.  This enables animation, styling, binding, etc...
    public static readonly DependencyProperty SourceObjectProperty =
        DependencyProperty.Register(
            nameof(SourceObject), 
            typeof(object), 
            typeof(ProxyBinding), 
            new PropertyMetadata(null));


}


<UserControl x:Class="WpfApp9.UCDG"
             xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
             xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" 
             xmlns:d="http://schemas.microsoft.com/expression/blend/2008" 
             xmlns:local="clr-namespace:WpfApp9"
             mc:Ignorable="d" 
             d:DesignHeight="450" d:DesignWidth="800">
    <UserControl.Resources>
        <local:ProxyBinding x:Key="ProxyBinding"
                            SourceObject="{Binding RelativeSource={RelativeSource AncestorType=UserControl}}"/>
    </UserControl.Resources>
    <Grid>
        <DataGrid ItemsSource="{Binding UCDGCollection,RelativeSource={RelativeSource AncestorType=UserControl}}"
                      VirtualizingPanel.IsVirtualizing="True"
                      VirtualizingPanel.VirtualizationMode="Recycling"
                      VirtualizingPanel.CacheLengthUnit="Item"
                      VirtualizingPanel.CacheLength="5,5"
                      ScrollViewer.CanContentScroll="True"
                      ScrollViewer.IsDeferredScrollingEnabled="True"
                      UseLayoutRounding="True"
                      SnapsToDevicePixels="True"
                      EnableRowVirtualization="True"
                      EnableColumnVirtualization="True"
                      AutoGenerateColumns="True"
                      CanUserAddRows="False"
                      >
            <DataGrid.ContextMenu>
                <ContextMenu>
                    <MenuItem FontSize="30"
                              Width="150"
                              Header="{Binding SourceObject.UCFirstHeader,Source={StaticResource ProxyBinding}}"
                              Command="{Binding SourceObject.UCFirstCmd,Source={StaticResource ProxyBinding}}"
                              CommandParameter="{Binding RelativeSource={RelativeSource AncestorType=ContextMenu},
                              Path=PlacementTarget.SelectedItems}"/>
                </ContextMenu>
            </DataGrid.ContextMenu>
            <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>
    </Grid>
</UserControl>

using System;
using System.Collections;
using System.Collections.Generic;
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;

namespace WpfApp9
{
    /// <summary>
    /// Interaction logic for UCDG.xaml
    /// </summary>
    public partial class UCDG : UserControl
    {
        public UCDG()
        {
            InitializeComponent();
        }




        public IList UCDGCollection
        {
            get { return (IList)GetValue(UCDGCollectionProperty); }
            set { SetValue(UCDGCollectionProperty, value); }
        }

        // Using a DependencyProperty as the backing store for UCDGCollection.  This enables animation, styling, binding, etc...
        public static readonly DependencyProperty UCDGCollectionProperty =
            DependencyProperty.Register(
                nameof(UCDGCollection), 
                typeof(IList), 
                typeof(UCDG), 
                new PropertyMetadata(null));




        public string UCFirstHeader
        {
            get { return (string)GetValue(UCFirstHeaderProperty); }
            set { SetValue(UCFirstHeaderProperty, value); }
        }

        // Using a DependencyProperty as the backing store for UCFirstHeader.  This enables animation, styling, binding, etc...
        public static readonly DependencyProperty UCFirstHeaderProperty =
            DependencyProperty.Register(
                nameof(UCFirstHeader), 
                typeof(string), 
                typeof(UCDG), 
                new PropertyMetadata(null));




        public ICommand UCFirstCmd
        {
            get { return (ICommand)GetValue(UCFirstCmdProperty); }
            set { SetValue(UCFirstCmdProperty, value); }
        }

        // Using a DependencyProperty as the backing store for UCFirstCmd.  This enables animation, styling, binding, etc...
        public static readonly DependencyProperty UCFirstCmdProperty =
            DependencyProperty.Register(
                nameof(UCFirstCmd), 
                typeof(ICommand), 
                typeof(UCDG), 
                new PropertyMetadata(null));
    }

    public class ProxyBinding : Freezable
    {
        protected override Freezable CreateInstanceCore()
        {
            return new ProxyBinding();
        }


        public object SourceObject
        {
            get { return (object)GetValue(SourceObjectProperty); }
            set { SetValue(SourceObjectProperty, value); }
        }

        // Using a DependencyProperty as the backing store for SourceObject.  This enables animation, styling, binding, etc...
        public static readonly DependencyProperty SourceObjectProperty =
            DependencyProperty.Register(
                nameof(SourceObject), 
                typeof(object), 
                typeof(ProxyBinding), 
                new PropertyMetadata(null));


    }
}

 

 

<Window x:Class="WpfApp9.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:WpfApp9"
        mc:Ignorable="d"
        Title="{Binding MainTitle}" WindowState="Maximized">
    <Window.DataContext>
        <local:MainVM/>
    </Window.DataContext>
    <Grid>
        <local:UCDG UCDGCollection="{Binding BooksCollection}"
                    UCFirstHeader="{Binding FirstHeader}"
                    UCFirstCmd="{Binding FirstCmd}"/>
    </Grid>
</Window>


using Microsoft.Win32;
using Newtonsoft.Json;
using System.Collections.ObjectModel;
using System.ComponentModel;
using System.Diagnostics;
using System.IO;
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.Xml;

namespace WpfApp9
{
    /// <summary>
    /// Interaction logic for MainWindow.xaml
    /// </summary>
    public partial class MainWindow : Window
    {
        public MainWindow()
        {
            InitializeComponent();
        }
    }

    public class MainVM : INotifyPropertyChanged
    {
        private static readonly HttpClient client = new HttpClient();
        private readonly object isLoadingLock = new object();
        private readonly SemaphoreSlim concurrentThrottle = new SemaphoreSlim(10, 10);
        private string originUrl = "http://localhost:51537/BookService.svc/getbookslist?cnt=";

        public MainVM()
        {
            if (DesignerProperties.GetIsInDesignMode(new DependencyObject()))
            {
                return;
            }
            _ = Task.Run(async () =>
            {
                while (true)
                {
                    await InitBooksCollectionAsync();
                    await Task.Delay(10000);
                }
            });
        }

        private DelCmd firstCmd;
        public DelCmd FirstCmd
        {
            get
            {
                if (firstCmd == null)
                {
                    firstCmd = new DelCmd(async (s) =>
                    {
                        await FirstCmdExecutedAsync(s);
                    });
                }
                return firstCmd;
            }
        }

        private async Task FirstCmdExecutedAsync(object? obj)
        {
            await Task.Run(() =>
            {
                var items = ((System.Collections.IList)obj).Cast<Book>()?.ToList();
                if (items == null || !items.Any())
                {
                    return;
                }
                string jsonStr = JsonConvert.SerializeObject(items, Newtonsoft.Json.Formatting.Indented);

                Application.Current?.Dispatcher?.InvokeAsync(() =>
                {
                    SaveFileDialog dlg = new SaveFileDialog();
                    dlg.Filter = $"Json Files|*.json";
                    dlg.FileName = $"Json_{DateTime.Now.ToString("yyyyMMddHHmmssffff")}";
                    if (dlg.ShowDialog() == true)
                    {
                        string jsonFile = dlg.FileName;
                        using (StreamWriter fs = new StreamWriter(jsonFile, false, Encoding.UTF8))
                        {
                            fs.WriteLine(jsonStr);
                        }
                        MessageBox.Show($"{DateTime.Now},save {items.Count} items in {jsonFile}");
                    }
                });
            }).ConfigureAwait(false);
        }

        private async Task InitBooksCollectionAsync(int cnt = 1000000)
        {
            if (!await concurrentThrottle.WaitAsync(20000))
            {
                return;
            }
            if (IsLoading)
            {
                return;
            }

            try
            {
                IsLoading = true;
                MainTitle = $"{DateTime.Now},loading...";
                List<Book>? bksList = null;
                await Task.Run(async () =>
                {
                    string requestUrl = $"{originUrl}{cnt}";
                    string jsonStr = await client.GetStringAsync(requestUrl);
                    if (string.IsNullOrWhiteSpace(jsonStr))
                    {
                        return;
                    }
                    bksList = JsonConvert.DeserializeObject<List<Book>>(jsonStr);
                }).ConfigureAwait(false);

                if (bksList != null && bksList.Any())
                {
                    Application.Current?.Dispatcher?.InvokeAsync(() =>
                    {
                        BooksCollection = new ObservableCollection<Book>(bksList);
                        MainTitle = $"{DateTime.Now}," +
                        $"{BooksCollection.Count} items," +
                        $"FirstId:{BooksCollection.FirstOrDefault()?.Id}," +
                        $"LastId:{BooksCollection.LastOrDefault()?.Id}";
                    }, System.Windows.Threading.DispatcherPriority.Background);
                }
            }
            catch (Exception ex)
            {
                MessageBox.Show($"{DateTime.Now},ex message:{ex.Message}");
            }
            finally
            {
                IsLoading = false;
                concurrentThrottle.Release();
            }
        }

        private string firstHeader = "Save In Json";
        public string FirstHeader
        {
            get
            {
                return firstHeader;
            }
            set
            {
                if (value != firstHeader)
                {
                    firstHeader = value;
                    OnPropertyChanged();
                }
            }
        }

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

        private string mainTitle = $"{DateTime.Now}";
        public string MainTitle
        {
            get
            {
                return mainTitle;
            }
            set
            {
                if(value!=mainTitle)
                {
                    mainTitle = 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 DelCmd : ICommand
    {
        private readonly Action<object?> execute;
        private readonly Func<object?, bool>? canExecute;
        public DelCmd(Action<object?> executeValue, Func<object?, bool>? canExecuteValue = null)
        {
            execute = executeValue ?? throw new ArgumentNullException(nameof(execute));
            canExecute = canExecuteValue;
        }

        public event EventHandler? CanExecuteChanged;

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

        public void Execute(object? parameter)
        {
            if (!CanExecute(parameter))
            {
                return;
            }

            if (Application.Current?.Dispatcher?.CheckAccess() == true)
            {
                execute?.Invoke(parameter);
            }
            else
            {
                Application.Current?.Dispatcher.Invoke(() =>
                {
                    execute.Invoke(parameter);
                });
            }
        }

        public void RaisedCanExecuteChanged()
        {
            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);
                });
            }
        }
    }
}

 

Install-Package Newtonsoft.Json