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

 public int ImgIdx
 {
     get
     {
         return imgIdx;
     }
     set
     {
         if(value!=imgIdx)
         {
             imgIdx = value;
             if(imgIdx<0)
             {
                 imgIdx = imgsCount - 1;
             }
             if(imgIdx>=imgsCount)
             {
                 imgIdx = 0;
             }
             OnPropertyChanged(nameof(ImgIdx));
             if(!isPaused)
             {
                 ImgUrl = imgsList[ImgIdx];
                 Title = ImgUrl;
             } 
         }
     }
 }

System.InvalidOperationException
HResult=0x80131509
Message=The calling thread cannot access this object because a different thread owns it.
Source=WindowsBase
StackTrace:
at System.Windows.Threading.Dispatcher.VerifyAccess()
at System.Windows.Window.set_Title(String value)
at WpfApp219.MainWindow.set_ImgIdx(Int32 value) in D:\C\WpfApp219\MainWindow.xaml.cs:line 77
at WpfApp219.MainWindow.Tmr_Elapsed(Object sender, ElapsedEventArgs e) in D:\C\WpfApp219\MainWindow.xaml.cs:line 104
at System.Timers.Timer.MyTimerCallback(Object state)

public int ImgIdx
{
    get
    {
        return imgIdx;
    }
    set
    {
        if(value!=imgIdx)
        {
            imgIdx = value;
            if(imgIdx<0)
            {
                imgIdx = imgsCount - 1;
            }
            if(imgIdx>=imgsCount)
            {
                imgIdx = 0;
            }
            OnPropertyChanged(nameof(ImgIdx));
            if(!isPaused)
            {
                Application.Current.Dispatcher.BeginInvoke(new Action(() =>
                {
                    ImgUrl = imgsList[ImgIdx];
                    Title = ImgUrl;
                })); 
            } 
        }
    }
}

 Application.Current.Dispatcher.BeginInvoke(new Action(() =>
 {
     ImgUrl = imgsList[ImgIdx];
     Title = ImgUrl;
 })); 

//xaml
<Window x:Class="WpfApp219.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:WpfApp219"
        mc:Ignorable="d" KeyDown="Window_KeyDown" WindowState="Maximized"
        Title="MainWindow" Height="450" Width="800">
    <Grid>
        <Image x:Name="img" Source="{Binding ImgUrl,Mode=TwoWay,UpdateSourceTrigger=PropertyChanged}"
               MouseWheel="img_MouseWheel" MouseDown="img_MouseDown" MouseUp="img_MouseUp"
               MouseMove="img_MouseMove">
            <Image.RenderTransform>
                <TransformGroup>
                    <ScaleTransform x:Name="scaler"/>
                    <TranslateTransform x:Name="translater"/>
                </TransformGroup>
            </Image.RenderTransform>
        </Image>
    </Grid>
</Window>




//cs
using System;
using System.Collections.Generic;
using System.ComponentModel;
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 System.IO;

namespace WpfApp219
{
    /// <summary>
    /// Interaction logic for MainWindow.xaml
    /// </summary>
    public partial class MainWindow : Window, INotifyPropertyChanged
    {
        public event PropertyChangedEventHandler PropertyChanged;
        private void OnPropertyChanged(string propName)
        {
            var handler = PropertyChanged;
            if (handler != null)
            {
                handler?.Invoke(this, new PropertyChangedEventArgs(propName));
            }
        }

        private string imgUrl;
        public string ImgUrl
        {
            get
            {
                return imgUrl;
            }
            set
            {
                if (value != imgUrl)
                {
                    imgUrl = value;
                    OnPropertyChanged(nameof(ImgUrl));
                    //this.Title = imgUrl;
                }
            }
        }

        private int imgIdx = 0;
        public int ImgIdx
        {
            get
            {
                return imgIdx;
            }
            set
            {
                if(value!=imgIdx)
                {
                    imgIdx = value;
                    if (imgIdx < 0)
                    {
                        imgIdx = imgsCount - 1;
                    }
                    if (imgIdx >= imgsCount)
                    {
                        imgIdx = 0;
                    }
                    OnPropertyChanged(nameof(ImgIdx));
                   
                    if (!isPaused)
                    {
                        Application.Current.Dispatcher.BeginInvoke(new Action(() =>
                        {
                            ImgUrl = imgsList[ImgIdx];
                            Title = ImgUrl;
                            ResetTransform();
                        }));
                    }
                }
            }
        } 
        
        private List<string> imgsList { get; set; }
        
        private int imgsCount = 0;
        private bool isPaused = false;
        private Point currentPt { get; set; }
        private bool isMoving = false;

        public MainWindow()
        {
            InitializeComponent();
            imgsList = new List<string>(Directory.GetFiles(@"..\..\Images"));
            imgsCount = imgsList.Count;
            ImgUrl = imgsList[imgIdx];            
            this.DataContext = this;
            System.Timers.Timer tmr = new System.Timers.Timer();
            tmr.Interval = 300;
            tmr.Elapsed += Tmr_Elapsed;
            tmr.Start();
        }

        private void Tmr_Elapsed(object sender, System.Timers.ElapsedEventArgs e)
        {
            ++ImgIdx;
        }

        private void ResetTransform()
        {
            scaler.ScaleX = 1.0;
            scaler.ScaleY = 1.0;
            scaler.CenterX = 0;
            scaler.CenterY = 0;
            translater.X = 0;
            translater.Y = 0;
        }

        private void img_MouseWheel(object sender, MouseWheelEventArgs e)
        {
            if (e.Delta > 0)
            {
                scaler.ScaleX *= 1.2;
                scaler.ScaleY *= 1.2;
            }
            else
            {
                scaler.ScaleX /= 1.2;
                scaler.ScaleY /= 1.2;
            }
            scaler.CenterX = e.GetPosition(img).X;
            scaler.CenterY = e.GetPosition(img).Y;
        }

        private void img_MouseDown(object sender, MouseButtonEventArgs e)
        {
            currentPt = e.GetPosition(img);
        }

        private void img_MouseUp(object sender, MouseButtonEventArgs e)
        {
            if(e.ChangedButton==MouseButton.Left && e.ButtonState==MouseButtonState.Released && isMoving)
            {
                Point newPt = e.GetPosition(img);
                translater.X += (newPt.X - currentPt.X) * scaler.ScaleX;
                translater.Y += (newPt.Y - currentPt.Y) * scaler.ScaleY;
            }
        }

        private void img_MouseMove(object sender, MouseEventArgs e)
        {
            isMoving = true;
        }

        private void Window_KeyDown(object sender, KeyEventArgs e)
        {
            if(e.Key==Key.Down)
            {
                ++ImgIdx;
            }
            else if ((e.Key == Key.Up))
            {
                --ImgIdx; 
            }
            else if(e.Key==Key.Space)
            {
                isPaused=!isPaused;
            }
        }
    }
}