ASP.NET Is there a better way to find controls that are within other controls?

I currently have a dropdown inside an ascx control. I need to “find” it from within the code behind on another ascx that is on the same page. It’s value is used as a param to an ObjectDataSource on ascx #2. I am currently using this ugly piece of code. It works but I realize if the conrtol order were to change or various other things, it wouldn’t be where I am expecting. Does anyone have any advice how I should properly be doing this?

Persist FileUpload Control Value

I have asp.net FileUpload control inside an update panel. When I click upload button, I am reading the file for some code, if code not found then I am showing ModalPopup for selecting a user from dropdown, otherwise uploading and emailing the file to user of that Code(this code is saved in Database).
If code not found,its displaying ModalPopup and removing the selected file, I want to persist the selected file after post back.
This is my code