Null Object Reference with SharedPreferences

Question

I have been banging my head on the keyboard for hours. I want to store an incremented integer for a separate stats activity in my app. I am trying to use Shared Preferences to achieve this. However in my latest attempt, which is the furthest I have gotten, the program throws an exception.

My code:

public class LootChest extends AppCompatActivity {
    public static final String prefName = "prefsFile";
    SharedPreferences settings = getApplicationContext().getSharedPreferences(prefName, 0); //line 25
    int rollCountS = settings.getInt("Roll Count", 0);
    int rollCount = 0; //to be incremented

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_loot_chest);
    }

    public void openChest(View v) {
        SharedPreferences.Editor editor = settings.edit();
        editor.putInt("Roll Count", rollCount);
        rollCount = rollCountS + 1;

The exception:

Caused by: java.lang.NullPointerException:
Attempt to invoke virtual method
'android.content.SharedPreferences android.content.Context
.getSharedPreferences(java.lang.String, int)'
on a null object reference at android.content.ContextWrapper
.getSharedPreferences(ContextWrapper.java:171)
at net.zingrook.mobiloot.LootChest.<init>(LootChest.java:25)

I've read dozens of threads on implementing this, and looked at the Android documentation and I am out of ideas. Thank you for any help.

I'm not an android programmer, but if the issue is the Context wrapper is null in class instantiation, is it possible the settings should be after the `onCreate` is called? — KevinO, May 25 '17 at 04:30

score 4 · Answer 1 · answered May 25 '17 at 04:30

You are initializing sharedPreference object before activity lifecycle could begin.

move the initialization into onCreate

public static final String prefName = "prefsFile";
    SharedPreferences settings;  //line 25
    int rollCountS;
    int rollCount = 0;
@Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_loot_chest);
        settings = getApplicationContext().getSharedPreferences(prefName, 0); 
    }

score 1 · Answer 2 · answered May 25 '17 at 04:30

Just change this your code in this way.

public class LootChest extends AppCompatActivity {
    public static final String prefName = "prefsFile";
    SharedPreferences settings;  //line 25
    int rollCountS;
    int rollCount = 0; //to be incremented

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_loot_chest);
        settings = getApplicationContext().getSharedPreferences(prefName, 0);
        rollCountS = settings.getInt("Roll Count", 0);
    }

score 0 · Answer 3 · answered May 25 '17 at 04:39

My Point of view

public class LootChest extends AppCompatActivity {
public static final String prefName = "prefsFile";
SharedPreferences settings;
SharedPreferences.Editor editor;
int rollCountS;
int rollCount = 0;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_loot_chest);
    settings=getApplicationContext().getSharedPreferences(prefName, 0);
    editor = settings.edit();
    rollCountS= settings.getInt("Roll Count", 0);
}

public void openChest(View v) {
    editor.putInt("Roll Count", rollCount);
    rollCount = rollCountS + 1;

Null Object Reference with SharedPreferences

3 Answers3