what is ids.xml used for?

Question

Just a quick question, what is the ids.xml used for when developing an Android app? I saw an example on the android resources webpage which contained:

Answer 1

Another application for id.xml is in respect to layouts and library projects. Let's say you specify a generic list of options in a library (dialog) layout

and handle these views in a generic (dialog) fragment

optionOneCheck = (CheckedTextView)rootView.findViewById(R.id.checked_option_one);
optionTwoCheck = (CheckedTextView)rootView.findViewById(R.id.checked_option_two);

If you remove any of the view declarations from a copy of the layout in a main project, you will get a "no such field" error exception at runtime.

The compiler doesn't complain, but at runtime the id isn't actually there/known.

Declaring the ids in id.xml and using

avoids the runtime error