how to catch a dynamically created custom component's event?

What I have is a wrapper custom component as a Canvas containing a DataGrid with a custom item renderer in the 1st column.   I'm inserting DataGridColumns into the DataGrid upon Canvas creationComplete.    Inside my expandBtnRenderer, I have it dispatchEvent("expandBtnPressed",new Event("expandBtnPressed")); question is....where do i add the eventListener for my custom event "expandBtnPressed" ?   my Canvas component: private function init():void {   var myXBRFactory:ClassFactory=new ClassFactory(expandBtnRenderer);   var newDGC:DataGridColumn=new DataGridColumn("expand");   newDGC.itemRenderer=myXBRFactory;   var newCols:Array=new Array();   newCols.push(newDGC);   dgHeader.columsn=newCols; } <mx:DataGrid id="dgHeader" dataProvider="{dataProvider}"/>