title: WPF DataGrid SelectedItems - keeping multiple selected while left clicking
body: <p>is there a way to mimic the behavior of ctrl+click which keeps previously selected rows selected and just adds more selected items? </p>
  
  <p>by default, when clicking on each row, all previously selected rows get de-selected. </p>
  
  <p>one way to achieve this, would be to override SelectionChanged event, and re-select removed rows. </p>
  
  <pre><code>void TestGrid_SelectionChanged(object sender, SelectionChangedEventArgs e) {
      foreach (var i in e.RemovedItems)
          TestGrid.SelectedItems.Add(i);
  
  }
  </code></pre>
  
  <p>This is not ideal however, because in some situations i would want to de-select rows (such as when clicking a toggle button in one of the columns). </p>