I want to change layout background in another Activity

Question

My app consists of multiple layouts and the layout ends with a finish() to avoid unnecessary reconnection when the back button is touched when switching layouts.

That's why I have an issue where the app reinitializes when turning off or switching the layout even if I change the value of a layout element like setText or setBackgorundColor.

So I would like to keep the theme selected by the user so that it can be used in a PreferenceFragment activity that has changed its value and saved even after exiting the app.

The problem is that in this PreferencFragment java class file I tried to change the values ​​of multiple layouts (setText or setBackground... something more), but nothing works.

Even if I use LayouInflater to get an element from another layout and set the setting to setText, the setting change does not take effect when exiting the PreferencesFragment window.

SettingFragment.java

    public class SettingFragment extends PreferenceFragment {

    private SharedPreferences pref;

    @Override
    public void onCreate(@Nullable Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        addPreferencesFromResource(R.xml.setting);
        pref = PreferenceManager.getDefaultSharedPreferences(getActivity());

    }
    @Override
    public void onResume() {
        super.onResume();
        pref.registerOnSharedPreferenceChangeListener(listener);
    }

    @Override
    public void onPause() {
        super.onPause();
        pref.unregisterOnSharedPreferenceChangeListener(listener);
    }
    SharedPreferences.OnSharedPreferenceChangeListener listener = new SharedPreferences.OnSharedPreferenceChangeListener() {
        @Override
        public void onSharedPreferenceChanged(SharedPreferences sharedPreferences, String key) {
            LayoutInflater inflater = (LayoutInflater)getActivity().getSystemService(Context.LAYOUT_INFLATER_SERVICE);
            View view = inflater.inflate(R.layout.activity_main,null);

            if(key.equals("theme")){
                String datas = pref.getString("theme", null);
                if(datas.equals("RED")){
                    Toast.makeText(getActivity(), "RED!", Toast.LENGTH_SHORT).show();
                    view.setBackgroundColor(Color.RED); // Nothing To change !!
                }
                else if(datas.equals("BLUE")){
                    Toast.makeText(getActivity(), "BLUE!", Toast.LENGTH_SHORT).show();
                }
                else if(datas.equals("GREEN")){
                    Toast.makeText(getActivity(), "GREEN!", Toast.LENGTH_SHORT).show();
                }
            }
        }
    };
}