OnSaveInstanceState with Singleton

Question

I have a Singleton Data class, which I use to store data. I'm accessing it in different `Fragment`s. When the first `Fragment` is loaded, it's no problem that all fields in the Singleton are `null`. When the second `Fragment` is shown, it depends on these fields to show its data. The first `Fragment` ensures these fields are initialized. However, when the user presses the home button in the second `Fragment`, and opens it again after like an hour or so, the Singleton has lost all its data, and the `Fragment` tries to access `null` fields. I wanted to implement the `onSaveInstanceState` method, but I'm stumped on how this works - I have no instance of the data to assign it to. ``` @Override public void onSaveInstanceState(Bundle outState) { super.onSaveInstanceState(outState); outState.putSerializable("DATA", Data.getInstance()); } @Override public void onCreate(Bundle savedInstanceState){ super.onCreate(savedInstanceState); savedInstanceState.getSerializable("DATA"); //What to do with…

Accepted Answer

Are the fragments both hosted in the same Activity? If so, why not store the shared state in a member of the Activity, and use the Activity's onSaveInstanceState() and onCreate() to save and restore it. In your fragments you can then do...

```
((MyActivityClass)getActivity()).getSharedState()
```

Otherwise, you could make your singleton object manage a member object that can be serialized and deserialized:

```
MySingleton.instance().saveTo(outState);
MySingleton.instance().restoreFrom(savedInstanceState);
MySingleton.instance().getState();
```

Where

```
public void restoreFrom(Bundle savedInstanceState) {
    mState = savedInstanceState.getSerializable("DATA");
}
```

OnSaveInstanceState with Singleton

Solution

Problem