NullPointerException getSupportFragmentManager() with Facebook onSessionStateChange

Question

I am using the Facebook SDK to do a FB login. Sometimes I receive a random NullPointerException when returning from the Facebook login.

The NPE is on my line:

FragmentManager fm = getActivity().getSupportFragmentManager();

My FB login is in a single Fragment. When the user logs into FB and is successful, it changes the Fragment to another. Why am I getting this NPE?

private void onSessionStateChange(Session session, SessionState state, Exception exception) {
    if (state.isOpened()) { 
        Log.i("Facebook", "Logged In");
        mPrefs.setFbLoggedIn(true);

        Request.newMeRequest(session, new Request.GraphUserCallback() {
            @Override
            public void onCompleted(GraphUser user, Response response) {
                if (response.getError() == null) {
                    FragmentManager fm = getActivity().getSupportFragmentManager();
                    FragmentTransaction ft = fm.beginTransaction();
                    ft.setCustomAnimations(R.anim.slide_in_right_to_left, R.anim.slide_out_right_to_left, 
                            R.anim.slide_in_right_to_left, R.anim.slide_out_right_to_left);
                    ft.remove(fm.findFragmentById(R.id.container));
                    ft.add(R.id.container, LoadingFragment.newInstance(), "loadingFragment");
                    ft.commit();

                    String fbId = "";
                    try { fbId = user.getId(); }
                    catch (NullPointerException e) { e.printStackTrace(); }

                    String fullName = "";
                    try { fullName = user.getName(); }
                    catch (NullPointerException e) { e.printStackTrace(); }

                    String email = "";
                    try { email = user.getProperty("email").toString(); }
                    catch (NullPointerException e) { e.printStackTrace(); }

                    String gender = "";
                    try { gender = user.getProperty("gender").toString(); }
                    catch (NullPointerException e) { e.printStackTrace(); }

                    String pictureUrl = "";
                    try { pictureUrl = "http://graph.facebook.com/" + user.getId() + "/picture?type=large"; }
                    catch (NullPointerException e) { e.printStackTrace(); }

                    String birthdate = "";
                    try {
                        if (user.getBirthday() != null && !user.getBirthday().isEmpty()) {
                            try { 
                                DateTime dateTime = DateTime.parse(user.getBirthday(), DateTimeFormat.forPattern("MM/dd/yyyy"));
                                DateTimeFormatter formatter = DateTimeFormat.forPattern("yyyy-MM-dd'T'HH:mm:ss.SSSZZ")
                                        .withZone(DateTimeZone.getDefault());
                                birthdate = formatter.print(dateTime);
                            } 
                            catch (IllegalArgumentException e) { e.printStackTrace(); }
                        }
                    }
                    catch (NullPointerException e) { e.printStackTrace(); }

                    User u = new User(fbId, email, fullName, gender, birthdate, pictureUrl);
                    FacebookMethods.writeFbInfo(getActivity(), u);

                    ((MainActivity)getActivity()).connectToServer();
                }
                else {
                    Toast.makeText(getActivity(), response.getError().getErrorMessage(), Toast.LENGTH_SHORT).show();
                }
            }
        }).executeAsync();
    } 
    else if (state.isClosed()) { 
        Log.i("Facebook", "Logged Out"); 
        mPrefs.setFbLoggedIn(false);
    }
}

Stacktrace (not full, but the important lines)

java.lang.NullPointerException
   at com.walintukai.lfdate.LoginFragment$2.onCompleted(LoginFragment.java:278)
   at com.facebook.Request$1.onCompleted(Request.java:303)
   at com.facebook.Request$4.run(Request.java:1726)
   at android.os.Handler.handleCallback(Handler.java:733)
   at android.os.Handler.dispatchMessage(Handler.java:95)
   at android.os.Looper.loop(Looper.java:136)
   at android.app.ActivityThread.main(ActivityThread.java:5050)
   at java.lang.reflect.Method.invokeNative(Method.java)
   at java.lang.reflect.Method.invoke(Method.java:515)
   at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:789)
   at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:605)
   at dalvik.system.NativeStart.main(NativeStart.java)

If it's on this line, it means `getActivity()` is null. It will happend if your `onCompleted` method gets called after your Activity being stopped/finished. Paste your full StackTrace — Simon Marquis, Aug 22 '14 at 21:01
@SimonMarquis I don't have the full stacktrace, but here are the first set of lines. Is this enough? — The Nomad, Aug 22 '14 at 21:04
definitively, your Activity is stopped. It will happend every time you press the back button too early. Your activity is stopped, onCompleted is called, getActivity() is null -> NullPointerException — Simon Marquis, Aug 22 '14 at 21:06
@SimonMarquis Explained very well! Thank you. So, to reiterate, the user is logging in with FB, and then when returning to my app, they pressed the back button too early before `onCompleted` was called? What would be the best way to put in an error check for this? — The Nomad, Aug 22 '14 at 21:10
Simply return from your method if getActivity() returns null — Simon Marquis, Aug 22 '14 at 21:11
@SimonMarquis Makes perfect sense! Thanks for the help! Please make an answer so I can accept it! — The Nomad, Aug 22 '14 at 21:14

score 2 · Accepted Answer · answered Aug 22 '14 at 21:17

The getActivity() here can return null if the Activity was stopped (back button, home, recent, ...).

To avoid error simply stop the method early:

   Request.newMeRequest(session, new Request.GraphUserCallback() {
        @Override
        public void onCompleted(GraphUser user, Response response) {
            if (getActivity() == null) {
                // The activity was stopped
                return;
            }
            // else we can continue 
            // ...
        }
    });

NullPointerException getSupportFragmentManager() with Facebook onSessionStateChange

1 Answers1