Hi

I am following the Force.com Workbook and I created a method to renumber the line items under the invoice Invoice and Line Item have a master detail view. The method is being called from a button on the Invoice and it works correctly (updated the Line Number beginning from 1).
The issue is that the line numbers do no always appear ordered in the App. Sometimes the Line Items come as 1,3,2,4.

How can i show these line items in order in the App?