doubleclick_to_edit.as

private function handleItemDoubleClick(event:ListEvent):void
{
	var dg:DataGrid = DataGrid(event.target);
	dg.editable = true;
	dg.editedItemPosition = event; // { rowIndex: event.rowIndex, columnIndex: event.columnIndex };
}

private function handleItemEditEnd(event:DataGridEvent):void
{
	var dg:DataGrid = DataGrid(event.target);
	dg.editable = false;
}

<mx:DataGrid 
	doubleClickEnabled="true"
	itemDoubleClick="handleItemDoubleClick(event)"
	itemEditEnd="handleItemEditEnd(event)"
>
...