Null Pointer in getApplicationContext()

Question

I'm trying the following piece of code, where a service is implementing my listener:

public class MyListenerClass extends Service implements MyListenerInterface {
    public void onCurrencyRecieved(MyEventClass event) {
        System.out.println("Coins Recieved - Listener Successful");
        stopSelf();
        Toast toast = Toast.makeText(getApplicationContext(), "Service Stopped", Toast.LENGTH_LONG);
        toast.show();        
    }

    @Override
    public void onCreate() {
        Toast toast = Toast.makeText(getApplicationContext(),"Service started", Toast.LENGTH_LONG);
        toast.show();
        super.onCreate();
    }

Now, the toast inside onCreate() is working fine, but that inside the overridden method is throwing the following exception:

01-03 18:52:35.740: ERROR/AndroidRuntime(2388): java.lang.NullPointerException
01-03 18:52:35.740: ERROR/AndroidRuntime(2388):     at android.content.ContextWrapper.getApplicationContext(ContextWrapper.java:100)
01-03 18:52:35.740: ERROR/AndroidRuntime(2388):     at com.test.listenertest1.MyListenerClass.onCurrencyRecieved(MyListenerClass.java:28)
01-03 18:52:35.740: ERROR/AndroidRuntime(2388):     at com.test.listenertest1.MyEventGenerator.generateEvent(MyEventGenerator.java:34)
01-03 18:52:35.740: ERROR/AndroidRuntime(2388):     at com.test.listenertest1.MyEventGenerator.<init>(MyEventGenerator.java:16)
01-03 18:52:35.740: ERROR/AndroidRuntime(2388):     at com.test.listenertest1.NewActivity.onKeyDown(NewActivity.java:33)
01-03 18:52:35.740: ERROR/AndroidRuntime(2388):     at android.view.KeyEvent.dispatch(KeyEvent.java:1037)
01-03 18:52:35.740: ERROR/AndroidRuntime(2388):     at android.app.Activity.dispatchKeyEvent(Activity.java:2046)
01-03 18:52:35.740: ERROR/AndroidRuntime(2388):     at com.android.internal.policy.impl.PhoneWindow$DecorView.dispatchKeyEvent(PhoneWindow.java:1631)
01-03 18:52:35.740: ERROR/AndroidRuntime(2388):     at android.view.ViewRoot.deliverKeyEventToViewHierarchy(ViewRoot.java:2368)
01-03 18:52:35.740: ERROR/AndroidRuntime(2388):     at android.view.ViewRoot.handleFinishedEvent(ViewRoot.java:2338)
01-03 18:52:35.740: ERROR/AndroidRuntime(2388):     at android.view.ViewRoot.handleMessage(ViewRoot.java:1641)
01-03 18:52:35.740: ERROR/AndroidRuntime(2388):     at android.os.Handler.dispatchMessage(Handler.java:99)

I guess I'm missing some important java concept. Cant we use getApplicationContext() inside an overridden method ?

Solution

You should try to avoid using getApplicationContext() as much as possible, as this will highly increase the chance of getting Force Closes.

Instead use YourClass.this, in this case MyListenerClass.this.

I guess in this example it doesn't work, because getApplicationContext() is called after stopSelf()

Comments

[Steve Blackwell]

Why does calling getApplicationContext() increase the chance of getting a Force Close?

[Force]

For example if you call it in an overriden OnClick Method it might - depending on the device/firmware/sdk - crash. Or see the code above: if this was used, it would not throw the Exception.

[Saurabh Verma]

I have tried using MyListenerClass.this and even removed stopself(). Still it is crashing giving the same log. Moreover I didnt see anything in the logs which suggests that it's a firmware crash

[Saurabh Verma]

Inside onCreate() I tried this: mContext = MyListenerClass.this; and then used mCOntext inside my overridden method. Still it's crashing

[Force]

Did you override onCurrencyRecieved? Because in the code above you didn't.

[Saurabh Verma]

onCurrencyRecieved is my listener method

[Force]

Have you tried replacing the toast with a Log.d(),? And if yes, did it still crash?