WPF KeyDown MVVM via CallMethodAction of behavior

 <behavior:Interaction.Triggers>
     <behavior:EventTrigger EventName="KeyDown">
         <behavior:CallMethodAction MethodName="WinKeyDown" TargetObject="{Binding}"/>
     </behavior:EventTrigger>
 </behavior:Interaction.Triggers>

<Window x:Class="WpfApp234.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:behavior="http://schemas.microsoft.com/xaml/behaviors"
        xmlns:local="clr-namespace:WpfApp234"
        mc:Ignorable="d"  WindowState="Maximized"
        Title="{Binding ImgUrl,Mode=TwoWay,UpdateSourceTrigger=PropertyChanged}" 
        Height="450" Width="800"> 
    <behavior:Interaction.Triggers>
        <behavior:EventTrigger EventName="KeyDown">
            <behavior:CallMethodAction MethodName="WinKeyDown" TargetObject="{Binding}"/>
        </behavior:EventTrigger>
    </behavior:Interaction.Triggers>
    <Grid>
        <Grid.Background>
            <ImageBrush ImageSource="{Binding ImgUrl,Mode=TwoWay,UpdateSourceTrigger=PropertyChanged}"/>
        </Grid.Background>
    </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;

namespace WpfApp234
{
    /// <summary>
    /// Interaction logic for MainWindow.xaml
    /// </summary>
    public partial class MainWindow : Window
    {
        public MainWindow()
        {
            InitializeComponent();
            var vm = new WinVM();
            this.DataContext = vm;
        }
    }

    public class WinVM : INotifyPropertyChanged
    {
        public WinVM()
        {
            InitData();
        }

        public void WinKeyDown(object sender, KeyEventArgs e)
        {
            switch (e.Key)
            {
                case Key.Up:
                    Idx++;
                    break;
                case Key.Down:
                    Idx--;
                    break;
                default:
                    break;
            }
        }

        private void InitData()
        {
            imgsList = new List<string>(System.IO.Directory.GetFiles(@"../../Images"));
            ImgUrl = imgsList[Idx];
            imgsCount = imgsList.Count;
        }

        private List<string> imgsList { get; set; }
        private int imgsCount { get; set; }

        private int idx = 0;
        public int Idx
        {
            get
            {
                return idx;
            }
            set
            {
                if (value != idx)
                {
                    idx = value;
                    if (idx >= imgsCount)
                    {
                        idx = 0;
                    }
                    if (idx < 0)
                    {
                        idx = imgsCount - 1;
                    }
                    ImgUrl = imgsList[idx];
                    OnPropertyChanged(nameof(Idx));
                }
            }
        }

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

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

    public class DelCmd : ICommand
    {
        public event EventHandler CanExecuteChanged
        {
            add
            {
                CommandManager.RequerySuggested += value;
            }
            remove
            {
                CommandManager.RequerySuggested -= value;
            }
        }

        private Action<object> execute;
        private Predicate<object> canExecute;

        public DelCmd(Action<object> executeValue, Predicate<object> canExecuteValue)
        {
            execute = executeValue;
            canExecute = canExecuteValue;
        }

        public DelCmd(Action<object> executeValue) : this(executeValue, null)
        {
        }

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

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