SharedPreferences always returning default value for custom object

Question

I am making a simple budget tracking app. I have a Budget class that stores a few variables: the amount, duration, and initial value of budget. I only have one global Budget object inside the fragment, called "budget", and am trying to get it to save. It seems to save fine, but when I try to retrieve it, it returns the default value for some reason. Here are my methods for saving and loading. I only call getBudget() in onCreateView, and only call saveBudget in onResume() and after the budget is edited. Note the log entries.

public void saveBudget(){
    SharedPreferences sharedPref = getActivity().getPreferences(Context.MODE_PRIVATE);
    SharedPreferences.Editor editor = sharedPref.edit();
    editor.clear();
    Gson gson = new Gson();
    String json = gson.toJson(budget);
    Log.d("BTAG", "JSON: " + json);
    editor.putString("current budget", json);
    editor.commit();
 }

public Budget getBudget(){
    SharedPreferences sharedPref = getActivity().getPreferences(Context.MODE_PRIVATE);
    Gson gson = new Gson();
    String json = sharedPref.getString("current budget", null);
    Log.d("BTAG", "gson from json: " + gson.fromJson(json, Budget.class));
    return gson.fromJson(json, Budget.class);
}

My log says this for my current instance of Budget:

D/BTAG: JSON: {"amount":35.92,"frequency":"monthly","originalAmount":35.92}
D/BTAG: gson from json: null

This shows that it saves without issue, but loading doesn't work. Why is getBudget() not working?

Answer 1

I think the problem might be in:

only call saveBudget in onResume()

1. You have to save the budget when the app is closing not in onResume() . Check this Android Activity Lifecycle .
2. Also, I think You shouldn't use hardcoded strings as key. Try to use string resources as in Android docs . If You make a mistake in 'key' You will get the default value.
3. If You save budget and then load it in another activity the problem might be in getting SharedPreferences instance. To get SharedPreferences use:

SharedPreferences sP = PreferenceManager.getDefaultSharedPreferences(getApplicationContext());

SharedPreferences from different activity

You can try this, I hope this will compile:

public static final String SHARED_PREFS = "NAME_OF_SP";
public static final String NAME_OF_VAL = "budget";

public void saveBudget()
{
    SharedPreferences sharedPref = getSharedPreferences(SHARED_PREFS, MODE_PRIVATE);
    SharedPreferences.Editor editor = sharedPref.edit();
    Gson gson = new Gson();
    String json = gson.toJson(budget);
    Log.d("BTAG", "JSON: " + json);
    editor.putString(NAME_OF_VAL, json);
    editor.apply();
}

public Budget getBudget()
{
    SharedPreferences sharedPref = getSharedPreferences(SHARED_PREFS, MODE_PRIVATE);
    Gson gson = new Gson();
    String json = sharedPref.getString(NAME_OF_VAL, null);
    Log.d("BTAG", "gson from json: " + gson.fromJson(json, Budget.class));
    return gson.fromJson(json, Budget.class);
}