title: cxGrid - Footer summary of checked records
body: <p>In cxGrid,I have a column that is boolean (properties : checkbox).
  How can I do a footer summary (SUM) of such a column i.e to sum how many records are checked.</p>
  
  <p>Right now, if I set it to SUM, my footer summary displays negative numbers for the items checked.How can I avoid these negative numbers?</p>
  
  <p>edit :
  I have found a would be solution on their site with :</p>
  
  <pre><code>procedure TForm1.cxGrid1DBTableView1DataControllerSummaryFooterSummaryItemsSummary(
    ASender: TcxDataSummaryItems; Arguments: TcxSummaryEventArguments;
    var OutArguments: TcxSummaryEventOutArguments);
  var
    si: TcxGridDBTableSummaryItem;
  begin
    si := Arguments.SummaryItem as TcxGridDBTableSummaryItem;
    if si.Column = cxGrid1DBTableView1Sonda then
      OutArguments.Done := not OutArguments.Value;
  end;
  </code></pre>
  
  <p>However I am getting the error :
  Could not convert variant of type (Null) into  type (Boolean).</p>
  
  <p>Dont understand this. Field is boolean type (bit).</p>
  
  <p>edit2:</p>
  
  <p>The problem is that sql server by default sets boolean type to NULL.
  That is why the conversion error. </p>