I don't think you would ever need to iterate through the contents of a user interface control to gather and/or manipulate the data bound to it. The GridPanel is for presentation, not backend logic so I would think that you would do this against the Store or DataSource that is bound to the GridPanel.
Can you give everyone a small sample of code on what you are trying to do and maybe someone can help you out?
In this moment my code is so complex.
But my intention is LOAD a SQLTABLE from DATABASE in a GRIDPANEL, then ALTER the data and SAVE the NEW DATA in DATABASE, but i have a framework to do a interface with a DATABASE, and i want freedom to manipulate the data.