Mi objeto contiene una cadena, larga e int. El objeto se llama Tracker y tengo un arrayList de Trackers. Cuando intento usar toJson me sale un error. Lo mismo con fromJson. Me sale esto cada vez.

FATAL EXCEPTION: main
 Process: com.example.unknownuser.scrapstable, PID: 13550
 java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.unknownuser.scrapstable/com.example.unknownuser.scrapstable.MainActivity}: java.lang.IllegalArgumentException: class android.content.res.ColorStateList declares multiple JSON fields named mChangingConfigurations
     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2646)
     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2707)
     at android.app.ActivityThread.-wrap12(ActivityThread.java)
     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1460)
     at android.os.Handler.dispatchMessage(Handler.java:102)
     at android.os.Looper.loop(Looper.java:154)
     at android.app.ActivityThread.main(ActivityThread.java:6077)
     at java.lang.reflect.Method.invoke(Native Method)
     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:866)
     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:756)
  Caused by: java.lang.IllegalArgumentException: class android.content.res.ColorStateList declares multiple JSON fields named mChangingConfigurations
     at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory.getBoundFields(ReflectiveTypeAdapterFactory.java:170)
     at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory.create(ReflectiveTypeAdapterFactory.java:100)
     at com.google.gson.Gson.getAdapter(Gson.java:423)
     at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory.createBoundField(ReflectiveTypeAdapterFactory.java:115)
     at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory.getBoundFields(ReflectiveTypeAdapterFactory.java:164)
     at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory.create(ReflectiveTypeAdapterFactory.java:100)
     at com.google.gson.Gson.getAdapter(Gson.java:423)
     at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory.createBoundField(ReflectiveTypeAdapterFactory.java:115)
     at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory.getBoundFields(ReflectiveTypeAdapterFactory.java:164)
     at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory.create(ReflectiveTypeAdapterFactory.java:100)
     at com.google.gson.Gson.getAdapter(Gson.java:423)
     at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory.createBoundField(ReflectiveTypeAdapterFactory.java:115)
     at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory.getBoundFields(ReflectiveTypeAdapterFactory.java:164)
     at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory.create(ReflectiveTypeAdapterFactory.java:100)
     at com.google.gson.Gson.getAdapter(Gson.java:423)
     at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory.createBoundField(ReflectiveTypeAdapterFactory.java:115)
     at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory.getBoundFields(ReflectiveTypeAdapterFactory.java:164)
     at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory.create(ReflectiveTypeAdapterFactory.java:100)
     at com.google.gson.Gson.getAdapter(Gson.java:423)
     at com.google.gson.internal.bind.CollectionTypeAdapterFactory.create(CollectionTypeAdapterFactory.java:53)
     at com.google.gson.Gson.getAdapter(Gson.java:423)
     at com.google.gson.Gson.fromJson(Gson.java:887)
     at com.google.gson.Gson.fromJson(Gson.java:853)
     at com.google.gson.Gson.fromJson(Gson.java:802)
     at com.example.unknownuser.scrapstable.MainActivity.onCreate(MainActivity.java:109)
     at android.app.Activity.performCreate(Activity.java:6662)
     at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1118)

Tengo la actividad A que intenta guardar la ArrayList of Trackers:

Tracker trax = new Tracker(description, timeToCount, imageID);
track.add(trax);

sharedPref = getSharedPreferences("pref", Context.MODE_PRIVATE);
editor = sharedPref.edit();
Gson gson = new Gson();
String json = gson.toJson(track);
editor.putString("LeftoverList", json);
editor.commit();

En la Actividad B, trato de recuperar la ArrayList of Trackers

ArrayList<Tracker> foodList;

sharedPref = getSharedPreferences("pref", Context.MODE_PRIVATE);
gson = new Gson();
json = sharedPref.getString("LeftoverList", " ");

type = new TypeToken<ArrayList<Tracker>>(){}.getType();
foodList = gson.fromJson(json, type);

Las líneas que usan los métodostoJson yfromJson me están dando las excepciones fatales. Muchas gracias por quien ayuda.