CachingPrefsAdapter.java

import android.content.SharedPreferences;
import android.support.annotation.NonNull;

import com.f2prateek.rx.preferences.Preference;

/**
 * Caches an result in memory to avoid fetching and parsing it for every call
 * IMPORTANT: the value will not update automatically if you change the preferences in another way than using
 * {@link Preference#set(Object)}
 * Created by timfreiheit on 05.12.15.
 */
public class CachingPrefsAdapter<T> implements Preference.Adapter<T> {

    Preference.Adapter<T> adapter;
    T t;

    public CachingPrefsAdapter(Preference.Adapter<T> adapter){
        this.adapter = adapter;
    }

    @Override
    public T get(@NonNull String key, @NonNull SharedPreferences preferences) {
        if (t == null) {
            t = adapter.get(key, preferences);
        }
        return t;
    }

    @Override
    public void set(@NonNull String key, @NonNull T value, @NonNull SharedPreferences.Editor editor) {
        t = value;
        adapter.set(key, value, editor);
    }
}

GsonPrefsAdapter.java

import android.content.SharedPreferences;
import android.support.annotation.NonNull;

import com.f2prateek.rx.preferences.Preference;
import com.google.gson.Gson;

/**
 * Preferences Adapter to use gson for serializing
 * Created by timfreiheit on 05.12.15.
 */
public class GsonPrefsAdapter<T> implements Preference.Adapter<T> {
    final Gson gson;
    private Class<T> clazz;
    private T defaultValue;

    public GsonPrefsAdapter(Class<T> clazz){
        this(new Gson(), clazz);
    }

    public GsonPrefsAdapter(Gson gson, Class<T> clazz){
        this(new Gson(), clazz, null);
    }

    public GsonPrefsAdapter(Gson gson, Class<T> clazz, T defaultValue){
        this.gson = gson;
        this.clazz = clazz;
        this.defaultValue = defaultValue;
    }

    @Override
    public T get(@NonNull String key, @NonNull SharedPreferences preferences) {
        String json = preferences.getString(key, null);
        if (json == null) {
            return defaultValue;
        }
        return gson.fromJson(json, clazz);
    }

    @Override
    public void set(@NonNull String key, @NonNull T value, @NonNull SharedPreferences.Editor editor) {
        editor.putString(key, gson.toJson(value));
    }
}