How to tell if a combobox/textbox was changed by the code or the user

In a form control i have a listview and some textboxes and comboboxes.
When a list item is selected i add the data to the textboxes so the user can change them. non of it is databound. all the changes are made in the code.
I wanted to know the best way to find out if i the checkbox_SelectedIndexChanged event was triggered by the code behind or the user. is this possible through either the sender object or EventArgs. i didnt want to have to set bool values or something like that every time i change the values from the code. prefer a solution where i only have to add code to the checkbox_SelectedIndexChanged() method.
NB: the initial use for this is just to enable a save and cancel button (without having to remeber and compare values). There will be other uses for this later on as well.



...