It is deprecated because Android moved to fragment-based activities. Calling findPreference(CharSequence) will still work in higher API levels. You are just encouraged to use fragments instead of a PreferenceActivity.
The reason for the deprecation can be found in the source:
This function is not relevant for a modern fragment-based PreferenceActivity.
In API 11+ you should use PreferenceFragment.
If you want to have your IDE ignore the error just add the following to your method: @SuppressWarnings("deprecation")