Flex - 如何对标题中使用项呈示器的datagrid列进行排序？

I am using an advanced data grid that is using a custom item renderer for the column heading and now sorting doesn't work. If I take out the custom renderer it works fine but I need it to work with the renderer. Does anyone know how to do this? I am new to Flex and ActionScript.I am using an advanced data grid that is using