title: How to get the current DataGrid row selected in extended selection mode?
body: <p>I have a <code>dataGrid</code> with the selection mode in extended, so I can select many rows.</p>
  
  <p>I have a style trigger, with a multi-value converter, to set the background color of the row according to some conditions.</p>
  
  <p>Well, in my probes, I pass three parameters: <code>ItemsSource</code>, <code>SelectedItems</code> and <code>selectedItem</code>. I notice the following behavior:</p>
  
  <p>When I select the first row, <code>ItemsSource</code> has all the rows of the <code>dataGrid</code>. This is correct. <code>SelectedItems</code> has 0 items and <code>selectedItem</code> is null. However, without do nothing, the code enter by second time in the converter, in this case <code>SelectedItem</code> is the item selected in the <code>dataGrid</code>, but <code>SelectedItems</code> has no items.</p>
  
  <p>When I select the second row, <code>SelectedItems</code> has one item, the first selected row of the <code>dataGrid</code>, and <code>selectedItem</code> has the first row too. In this case the code does not enter by second time in the converter.</p>
  
  <p>When I select the third row, <code>SelectedItems</code> has two items, the first and the second row selected, but not the third. <code>SelectedItem</code> has the first row selected.</p>
  
  <p>So I see that <code>SelectedItem</code> alway has the first row selected and <code>SelectedItems</code> has the n-1 selected rows.</p>
  
  <p>But how can I know what is the current selected row? The new row?</p>