DMS/DMS.WPF/Helper/SelectedItemsBehavior.cs

using System.Collections;
using System.Windows;
using System.Windows.Controls;
using Microsoft.Xaml.Behaviors;

namespace DMS.WPF.Helper
{
    public class SelectedItemsBehavior : Behavior<DataGrid>
    {
        public static readonly DependencyProperty SelectedItemsProperty =
            DependencyProperty.Register(nameof(SelectedItems), typeof(IList), typeof(SelectedItemsBehavior),
                new FrameworkPropertyMetadata(null, FrameworkPropertyMetadataOptions.BindsTwoWayByDefault));

        public IList SelectedItems
        {
            get => (IList)GetValue(SelectedItemsProperty);
            set => SetValue(SelectedItemsProperty, value);
        }

        protected override void OnAttached()
        {
            base.OnAttached();
            AssociatedObject.SelectionChanged += OnSelectionChanged;
        }

        protected override void OnDetaching()
        {
            base.OnDetaching();
            if (AssociatedObject != null)
            {
                AssociatedObject.SelectionChanged -= OnSelectionChanged;
            }
        }

        private void OnSelectionChanged(object sender, SelectionChangedEventArgs e)
        {
            if (sender is DataGrid dataGrid)
            {
                SelectedItems = dataGrid.SelectedItems;
            }
        }
    }
}