What causes a fragment to get detached from an Activity?

Question

I have a SignupActivity which will go through several fragments as users go through a signup process. On the last fragment, I'm calling

getActivity().setResult(Activity.RESULT_OK) 

since SingupActivity intent was started for result. Some users are crashing at this point, because getActivity() is producing a NPE. I'm not able to figure out what is causing this. Screen rotation is disabled, so there is no reason that I know of for the fragment to detach from the Activity.

Any insight as to what may be causing this, and how I can resolve it?

public class SignupConfirmationFragment extends Fragment {
    public static final String TAG = SignupConfirmationFragment.class.getSimpleName();
    private User mNewUser;
    private myAppClient mmyAppClient;

    private Animation rotateAnimation;
    private ImageView avatar;

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        mNewUser = ((SignUpActivity) getActivity()).getNewUser();
        mmyAppClient = ((SignUpActivity) getActivity()).getmyAppClient();
    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
        final View v = inflater.inflate(R.layout.fragment_signup_confirmation, null);

        ((TextView) v.findViewById(R.id.username_textView)).setText(((SignUpActivity) getActivity()).getNewUser().getName());
        avatar = (ImageView) v.findViewById(R.id.avatar);

        if (mNewUser.getAvatarImage() != null) {
            avatar.setImageBitmap(mNewUser.getAvatarImage());
        }


        rotateAnimation = AnimationUtils.loadAnimation(getActivity(), R.anim.progress_rotate);
        v.findViewById(R.id.progress_loading).startAnimation(rotateAnimation);

        if (mNewUser.getAvatarImage() != null) {
            startAvatarUpload();
        } else if (mNewUser.getNewsletter()) {
            setNewsletterStatus();
        } else {
            pauseForOneSecond();
        }

        return v;
    }

    private void startAvatarUpload() {
        mmyAppClient.uploadUserAvatar(mNewUser.getAvatarImage(), new FutureCallback<JsonObject>() {
                    @Override
                    public void onCompleted(Exception e, JsonObject result) {
                        if (mNewUser.getNewsletter()) {
                            setNewsletterStatus();
                        } else {
                            updateFragment();
                        }
                    }
                },
                null,
                null);
    }

    private void setNewsletterStatus() {
        mmyAppClient.setNewsletter(mNewUser.getEmail(), mNewUser.getFirstName(), mNewUser.getLastName(), new FutureCallback<String>() {
            @Override
            public void onCompleted(Exception e, String result) {
                //Log.d(TAG, "Result: " + result);
                updateFragment();
            }
        });
    }

    private void pauseForOneSecond() {
        final Handler handler = new Handler();
        handler.postDelayed(new Runnable() {
            @Override
            public void run() {
                updateFragment();
            }
        }, 1000);
    }

    private void updateFragment() {
        rotateAnimation.cancel();
        if (isAdded()) {
            getActivity().setResult(Activity.RESULT_OK);
            AnalyticsManager.logUIEvent("sign up completed");
            getActivity().finish();
        } else {
            AnalyticsManager.logUIEvent("sign up failed");
        }

    }
}

Answer 1

According to Fragment lifecycle in Android OS, you cannot get the Activity associated with the fragment in the onCreateView, because the Activity with which the Fragment is associated will not be created at that stage.

See the figure below:

Also, refer to this link, http://developer.android.com/guide/components/fragments.html

As you can see the Activity is created in onActivityCreated which is after onCreateView, hence you'll get null if you try to call the Activity in the onCreateView. Try to call it in onActivityCreated or in onStart that should solve your problem.

I hope this helps.