Act whenever a selection is made or unmade (by the checking or unchecking of a checkbox perhaps) at a DevExpress ASPxGridView.

Wire up an event on the C# side like so:

MyGrid.ClientSideEvents.SelectionChanged = "function(s,e){{ActOut(s,e);}}";

 
 

There needs to be a dance partner on the JavaScript side:

function ActOut(s, e) {
   alert(s.GetSelectedRowCount());
}

 
 

In this example whenever a selection is made or unmade the count of total selections will bubble up in an alert.