title: WPF DevExpress Grid date filterstring
body: <p>I'm trying to apply filter parameters from a little form to a DevExpress grid.
  I did this by binding the FilterString from the grid to a string in the ViewModel.</p>
  
  <p>​currently I construct the filterstring as follows:
  ​</p>
  
  <pre><code>filterString += "[" + column.Header + "] &gt;= '" 
                  + ((DateTime)searchParameter).ToString("dd-MM-yyyy") 
                  + "' AND [" + column.Header + "] &lt; '" 
                  + ((DateTime)searchParameter).AddDays(1).ToString("dd-MM-yyyy") 
                  + "'";
  </code></pre>
  
  <p>in which the column header and field name come from the columnMap and the <code>searchParameter</code> is the date to filter on.</p>
  
  <p>The filter is applied correctly and also shown in the bottom of the grid. You can also edit it, but only string values are shown in the
  filter row at the top of the grid. Dates or Numbers aren't shown there. </p>
  
  <p>How can I also get dates and numbers to show in the filter row if
  I set a filterstring?</p>
  
  <p>It currently looks like this when filtering on name (data edited out):
  <a href="https://i.stack.imgur.com/eo7qp.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/eo7qp.png" alt="enter image description here"></a></p>