using System.Collections.ObjectModel;
using System.ComponentModel;
using System.Runtime.CompilerServices;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Data;

namespace WpfApp028
{
  public class ViewModel: INotifyPropertyChanged
  {
    public ViewModel()
    {
      for (int i = 1; i < 10; i++) col.Add(new Data() { ID = i, Name = $"Row {i}" });
      cvs.Source = col;
    }

    private ObservableCollection<Data> col = new ObservableCollection<Data>();
    private CollectionViewSource cvs = new CollectionViewSource();

    public ICollectionView View { get => cvs.View; }

    private int _rowCount;
    public int RowCount
    {
      get => this._rowCount;
      set
      {
        this._rowCount = value;
        OnPropertyChanged();
      }
    }
    #region attached property
    public static readonly DependencyProperty AttPropProperty =
        DependencyProperty.RegisterAttached("AttProp", typeof(bool), typeof(ViewModel), new PropertyMetadata(false, OnPropChanged));
    public static bool GetAttProp(DependencyObject obj) => (bool)obj.GetValue(AttPropProperty);
    public static void SetAttProp(DependencyObject obj, bool par) => obj.SetValue(AttPropProperty, par);
    private static void OnPropChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
    {
      DataGrid dg = d as DataGrid;
      if (dg == null) return;
      dg.SelectionChanged += (s, mbe) => ((ViewModel)(dg.DataContext)).RowCount = (int)(dg.SelectedItems).Count;
    }
    #endregion

    public event PropertyChangedEventHandler PropertyChanged;
    private void OnPropertyChanged([CallerMemberName] string propName = "") => PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propName));

  }
  public class Data
  {
    public int ID { get; set; }
    public string Name { get; set; }

  }
}