WPF Filtering DataGrid

I use the following code for testing. If it meets your needs, you could refer to it.
MainWindow.xaml:

 <StackPanel>  
    <TextBox Text="{Binding TextSearch,UpdateSourceTrigger=PropertyChanged}"/>  
    <DataGrid  Name="datagrid" VerticalAlignment="Top"  SelectedItem="{Binding SelectedEmployee}"   
              ItemsSource="{Binding View}" AutoGenerateColumns="False" ScrollViewer.VerticalScrollBarVisibility="Visible"  >  
        <DataGrid.Columns>  
            <DataGridTextColumn Header="FirstName" Binding="{Binding FirstName}" Width="80"/>  
        </DataGrid.Columns>  
    </DataGrid>  
</StackPanel>  

MainWindow.xaml.cs:

public partial class MainWindow : Window  
  {  
    public MainWindow()  
    {  
      InitializeComponent();  
      DataContext = new EmployeeListViewModel();  
    }  
  }  
  class EmployeeListViewModel : INotifyPropertyChanged  
  {  
    public event PropertyChangedEventHandler PropertyChanged;  

    public void OnPropertyChanged(String info)  
    {  
      if (PropertyChanged != null)  
      {  
        PropertyChanged(this, new PropertyChangedEventArgs(info));  
      }  
    }  
    public EmployeeListViewModel()  
    {  
      EmployeeList = new ObservableCollection<Employee>(GetEmployees());  

      this._view = new ListCollectionView(this.employeeList);  
      this._view.Filter=Filter;  
    }  
    private bool Filter(object item)  
    {  
      if(String.IsNullOrEmpty(TextSearch))  
        return true;  
      else  
        return((item as Employee).FirstName.IndexOf(TextSearch,StringComparison.OrdinalIgnoreCase) >=0);  
    }  
    private ObservableCollection<Employee> employeeList;  
    public ObservableCollection<Employee> EmployeeList  
    {  
      get { return employeeList; }  
      set  
      {  
        employeeList = value;  
        OnPropertyChanged("EmployeeList");  
      }  
    }  
    private ListCollectionView _view;  
    public ICollectionView View  
    {  
      get { return this._view; }  
    }  

    private string _TextSearch;  
    public string TextSearch  
    {  
      get { return _TextSearch; }  
      set  
      {  
        _TextSearch = value;  
        OnPropertyChanged("TextSearch");  
        View.Refresh();  
      }  
    }  
    private List<Employee> GetEmployees()  
    {  
      var mylist = new List<Employee>();  
      for(int i = 1; i < 500; i++)  
      {  
        mylist.Add(new Employee() { FirstName = $"nummer{i}" });  
      }  
      return mylist;  
    }  
  }  
  public class Employee  
  {  
    string firstname;  

    public string FirstName  
    {  
      get { return firstname; }  
      set { firstname = value; }  
    }  
  }  

The result:

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