Datagrid loaded

I'm loading items into a datagrid via xml. Then i'm performing some functions involving column names etc. How would i check the datagrid has finished loading because at the moment i get "undefined" returned because the data is not loaded.
Would it be something like:

var changeListener = new Object();
changeListener.change = function(event) {
var crossTab = items_dg.getColumnAt(1).columnName;
trace(crossTab);
};
items_dg.addEventListener("change", changeListener);

but with a different broadcast check? I couldnt find a broadcast under dataGrid that would change once it's loaded.
Thanks for any help!