Wpf Dispatcher.BeginInvoke((Action)delegate{}));

<Window x:Class="WpfApplication1.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:WpfApplication1"
        mc:Ignorable="d"
        Title="MainWindow" Height="350" Width="525">
    <Grid>
        <Grid.RowDefinitions>
            <RowDefinition/>
            <RowDefinition/>
            <RowDefinition/>
        </Grid.RowDefinitions>
        <Grid.ColumnDefinitions>
            <ColumnDefinition/>
            <ColumnDefinition/>
        </Grid.ColumnDefinitions>
        <Button Grid.Row="0" Grid.Column="0" Command="{Binding ClickCmd}" Content="Click Cmd"/>
        <Button Grid.Row="0" Grid.Column="1" Command="{Binding CancelCmd}" Content="Cancel Cmd"/>
        <ListBox Grid.Row="1" BorderBrush="Black" BorderThickness="3" Grid.RowSpan="2" ItemsSource="{Binding ContentOb,Mode=TwoWay,UpdateSourceTrigger=PropertyChanged}"/>
    </Grid>
</Window>

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Input;

namespace WpfApplication1.Model
{
    public class DelegateCommand : ICommand
    {
        private readonly Predicate<object> _canExecute;
        private readonly Action<object> _execute;

        public event EventHandler CanExecuteChanged;

        public DelegateCommand(Action<object> execute)
                       : this(execute, null)
        {
        }

        public DelegateCommand(Action<object> execute,
                       Predicate<object> canExecute)
        {
            _execute = execute;
            _canExecute = canExecute;
        }

        public  bool CanExecute(object parameter)
        {
            if (_canExecute == null)
            {
                return true;
            }

            return _canExecute(parameter);
        }

        public  void Execute(object parameter)
        {
            _execute(parameter);
        }

        public void RaiseCanExecuteChanged()
        {
            if (CanExecuteChanged != null)
            {
                CanExecuteChanged(this, EventArgs.Empty);
            }
        }
    }
}

 using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.ComponentModel;
using WpfApplication1.Model;
using System.Collections.ObjectModel;
using System.Threading;
using System.Windows; 
using System.IO;
using Newtonsoft.Json;

namespace WpfApplication1.ViewModel
{
    public class WpfVM : INotifyPropertyChanged
    {
        private WpfVM()
        {

        }
        public event PropertyChangedEventHandler PropertyChanged;

        public void OnPropertyChanged(string propName)
        {
            var handler = PropertyChanged;
            if(handler!=null)
            {
                handler?.Invoke(this, new PropertyChangedEventArgs(propName));
            }
        }

        private static WpfVM Wpfvm;
        private static readonly object objLock = new object();
        public static WpfVM GetWpfVM()
        {
            lock(objLock)
            {
                if(Wpfvm == null)
                {
                    Wpfvm = new WpfVM();
                }
                return Wpfvm;
            }
        }

        private static CancellationTokenSource cts=new CancellationTokenSource();

        #region Commands
        private DelegateCommand ClickCmdValue;
        public DelegateCommand ClickCmd
        {
            get
            {
                if(ClickCmdValue==null)
                {
                    ClickCmdValue = new DelegateCommand(ClickCmdExecuted);
                }
                return ClickCmdValue;
            }
        }

        private string ContentValue;
        public string Content
        {
            get
            {
                return ContentValue;
            }
            set
            {
                if(value!=ContentValue)
                {
                    ContentValue = value;
                    OnPropertyChanged("Content");
                }
            }
        }


        private bool IsCancelledValue=false;
        public bool IsCancelled
        {
            get
            {
                return IsCancelledValue;
            }
            set
            {
                if(value!=IsCancelledValue)
                {
                    IsCancelledValue = value;
                    OnPropertyChanged("IsCancelled");
                }
            }
        }
        private void ClickCmdExecuted(object obj)
        {
            ContentOb = new ObservableCollection<string>();
            Task.Run(() =>
            {
                while (!cts.IsCancellationRequested)
                {
                    Content = DateTime.Now.ToString("yyyyMMddHHmmssffff");
                    App.Current.Dispatcher.BeginInvoke((Action)delegate
                    {
                        ContentOb.Add(Content);
                    });
                    System.Diagnostics.Debug.WriteLine(Content);
                }
            },cts.Token);                      
        }

        private DelegateCommand CancelCmdValue;
        public DelegateCommand CancelCmd
        {
            get
            {
                if(CancelCmdValue==null)
                {
                    CancelCmdValue = new DelegateCommand(CancelCmdValueExecuted);
                }
                return CancelCmdValue;
            }
        }

        private void CancelCmdValueExecuted(object obj)
        {
            cts.Cancel();
            IsCancelled = true;
            System.Diagnostics.Debug.WriteLine("Cancelled!");
            string msJsonSerializerString = JsonConvert.SerializeObject(ContentOb,Formatting.Indented);
            string fileName = DateTime.Now.ToString("yyyyMMddHHmmssffff") + ".txt";
            using(StreamWriter streamWriter=new StreamWriter(fileName,true,Encoding.UTF8))
            {
                streamWriter.WriteLine(msJsonSerializerString);
            }
        }
        #endregion

        #region Properties
        private ObservableCollection<string> ContentObValue;
        public ObservableCollection<string> ContentOb
        {
            get
            {                 
                return ContentObValue;
            }
            set
            {
                if(value!=ContentObValue)
                {
                    ContentObValue = value;
                    OnPropertyChanged("ContentOb");
                }
            }
        }
        #endregion
    }
}

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
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 WpfApplication1.ViewModel;

namespace WpfApplication1
{
    /// <summary>
    /// Interaction logic for MainWindow.xaml
    /// </summary>
    public partial class MainWindow : Window
    {
        public MainWindow()
        {
            InitializeComponent();
            WpfVM vm = WpfVM.GetWpfVM();
            this.DataContext = vm;
        }
    }
}

private void ClickCmdExecuted(object obj)
{
ContentOb = new ObservableCollection<string>();
Task.Run(() =>
{
while (!cts.IsCancellationRequested)
{
Content = DateTime.Now.ToString("yyyyMMddHHmmssffff");
App.Current.Dispatcher.BeginInvoke((Action)delegate
{
ContentOb.Add(Content);
});
System.Diagnostics.Debug.WriteLine(Content);
}
},cts.Token);
}