Working with fragments - NullPointerException

Question

I received a null pointer exception error on my activity that holds various fragments. In that activity a list of users would be populated to the current users through parse based around various criteria like gender, minimum age, etc.

Below is the logcat message I unexpectedly received when launching my application.

08-15 17:42:28.863: E/AndroidRuntime(4974): FATAL EXCEPTION: main
08-15 17:42:28.863: E/AndroidRuntime(4974): Process: com.dooba.beta, PID: 4974
08-15 17:42:28.863: E/AndroidRuntime(4974): java.lang.NullPointerException
08-15 17:42:28.863: E/AndroidRuntime(4974):     at com.dooba.beta.Fragment1$1.done(Fragment1.java:108)
08-15 17:42:28.863: E/AndroidRuntime(4974):     at com.parse.FindCallback.internalDone(FindCallback.java:45)
08-15 17:42:28.863: E/AndroidRuntime(4974):     at com.parse.FindCallback.internalDone(FindCallback.java:1)
08-15 17:42:28.863: E/AndroidRuntime(4974):     at com.parse.Parse$6$1.run(Parse.java:888)
08-15 17:42:28.863: E/AndroidRuntime(4974):     at android.os.Handler.handleCallback(Handler.java:733)
08-15 17:42:28.863: E/AndroidRuntime(4974):     at android.os.Handler.dispatchMessage(Handler.java:95)
08-15 17:42:28.863: E/AndroidRuntime(4974):     at android.os.Looper.loop(Looper.java:136)
08-15 17:42:28.863: E/AndroidRuntime(4974):     at android.app.ActivityThread.main(ActivityThread.java:5017)
08-15 17:42:28.863: E/AndroidRuntime(4974):     at java.lang.reflect.Method.invokeNative(Native Method)
08-15 17:42:28.863: E/AndroidRuntime(4974):     at java.lang.reflect.Method.invoke(Method.java:515)
08-15 17:42:28.863: E/AndroidRuntime(4974):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:779)
08-15 17:42:28.863: E/AndroidRuntime(4974):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:595)
08-15 17:42:28.863: E/AndroidRuntime(4974):     at dalvik.system.NativeStart.main(Native Method)

Below is the activity code that holds the fragment where the error occured

 public class usermatch extends FragmentActivity {
        private PageAdapter mPagerAdapter;
        @Override
        protected void onCreate(Bundle savedInstanceState) {
            super.onCreate(savedInstanceState);
            setContentView(R.layout.viewpager_layout);
            initialisePaging();

        }

        private void initialisePaging() {
            // TODO Auto-generated method stub
            List<Fragment> fragments = new Vector<Fragment>();
            fragments.add(Fragment.instantiate(this, Fragment1.class.getName()));
            fragments.add(Fragment.instantiate(this, Fragment2.class.getName()));
            fragments.add(Fragment.instantiate(this, Fragment3.class.getName()));
            mPagerAdapter = new PageAdapter(this.getSupportFragmentManager(), fragments);
            ViewPager pager = (ViewPager) findViewById(R.id.viewpager);
            pager.setAdapter(mPagerAdapter);

        }

        @Override
        public boolean onCreateOptionsMenu(Menu menu) {

            // Inflate the menu; this adds items to the action bar if it is present.
            getMenuInflater().inflate(R.menu.mood, menu);
            return true;
        }

        @Override
        public boolean onOptionsItemSelected(MenuItem item) {
            // Handle action bar item clicks here. The action bar will
            // automatically handle clicks on the Home/Up button, so long
            // as you specify a parent activity in AndroidManifest.xml.
            int id = item.getItemId();
            if (id == R.id.action_settings) {
                return true;
            }
            return super.onOptionsItemSelected(item);
        }
    }

Below is the fragment activity code where I believe the error is triggered

    public class Fragment1 extends Fragment {
    private String currentUserId;
    private ArrayAdapter<String> namesArrayAdapter;
    private ArrayList<String> names;
    private ListView usersListView;
    private Button logoutButton;
    String userGender = ParseUser.getCurrentUser().getString("Gender");
    String activityName = ParseUser.getCurrentUser().getString("ActivityName");
    Number maxDistance = ParseUser.getCurrentUser().getNumber("Maximum_Distance");


    String userLookingGender = ParseUser.getCurrentUser().getString("Looking_Gender");
    Number minimumAge = ParseUser.getCurrentUser().getNumber("Minimum_Age");
    Number maximumAge = ParseUser.getCurrentUser().getNumber("Maximum_Age");
    Number userage = ParseUser.getCurrentUser().getNumber("Age");


    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
            Bundle savedInstanceState) {
        // TODO Auto-generated method stub
        if (container == null){
            return null;
        }
        setConversationsList();

        return (LinearLayout)inflater.inflate(R.layout.fragment1_layout, 
                container,false);

}
private void setConversationsList() {
    currentUserId = ParseUser.getCurrentUser().getObjectId();
    names = new ArrayList<String>();
    // String userActivitySelectionName = null;

    ParseQuery<ParseUser> query = ParseUser.getQuery();

    //  query.whereEqualTo("ActivityName",userActivitySelectionName);

    query.whereNotEqualTo("objectId", ParseUser.getCurrentUser().getObjectId());
    // users with Gender = currentUser.Looking_Gender
    query.whereEqualTo("Gender", userLookingGender);
    // users with Looking_Gender = currentUser.Gender
    query.whereEqualTo("Looking_Gender", userGender);
    query.setLimit(1);
    query.whereEqualTo("ActivityName", activityName);
    query.whereGreaterThanOrEqualTo("Minimum_Age", minimumAge).whereGreaterThanOrEqualTo("Age", userage);
    query.whereLessThanOrEqualTo("Maximum_Age", maximumAge).whereLessThanOrEqualTo("Age", userage);
    //  query.whereWithinKilometers("Maximum_Distance", point, maxDistance)





    query.findInBackground(new FindCallback<ParseUser>() {

        public void done(List<ParseUser> userList, ParseException e) {
            if (e == null) {
                for (int i=0; i<userList.size(); i++) {
                    names.add(userList.get(i).get("Name").toString());
                    names.add(userList.get(i).get("Headline").toString());
                    names.add(userList.get(i).get("Age").toString());

                    //       names.add(userList.get(i).getParseObject("ProfilePicture").;


                }




                usersListView = (ListView)getActivity().findViewById(R.id.usersListView);
                namesArrayAdapter =
                        new ArrayAdapter<String>(getActivity().getApplicationContext(),
                                R.layout.user_list_item, names);
                usersListView.setAdapter(namesArrayAdapter);

                usersListView.setOnItemClickListener(new AdapterView.OnItemClickListener() {
                    @Override
                    public void onItemClick(AdapterView<?> a, View v, int i, long l) {
                        openConversation(names, i);
                    }
                });

            } else {
                Toast.makeText(getActivity().getApplicationContext(),
                        "Error loading user list",
                        Toast.LENGTH_LONG).show();
            }
        }
    });
}

    public void openConversation(ArrayList<String> names, int pos) {
        ParseQuery<ParseUser> query = ParseUser.getQuery();
        query.whereEqualTo("Name", names.get(pos));
        query.findInBackground(new FindCallback<ParseUser>() {
            public void done(List<ParseUser> user, ParseException e) {
                if (e == null) {
                    Intent intent = new Intent(getActivity().getApplicationContext(), MessagingActivity.class);
                    intent.putExtra("RECIPIENT_ID", user.get(0).getObjectId());
                    startActivity(intent);
                } else {
                    Toast.makeText(getActivity().getApplicationContext(),
                            "Error finding that user",
                            Toast.LENGTH_SHORT).show();
                }
            }

        });
    }
    }

Update Logcat message

08-15 19:23:27.195: E/AndroidRuntime(1340): FATAL EXCEPTION: main
08-15 19:23:27.195: E/AndroidRuntime(1340): Process: com.dooba.beta, PID: 1340
08-15 19:23:27.195: E/AndroidRuntime(1340): java.lang.NullPointerException
08-15 19:23:27.195: E/AndroidRuntime(1340):     at com.dooba.beta.Fragment1$1.done(Fragment1.java:108)
08-15 19:23:27.195: E/AndroidRuntime(1340):     at com.parse.FindCallback.internalDone(FindCallback.java:45)
08-15 19:23:27.195: E/AndroidRuntime(1340):     at com.parse.FindCallback.internalDone(FindCallback.java:1)
08-15 19:23:27.195: E/AndroidRuntime(1340):     at com.parse.Parse$6$1.run(Parse.java:888)
08-15 19:23:27.195: E/AndroidRuntime(1340):     at android.os.Handler.handleCallback(Handler.java:733)
08-15 19:23:27.195: E/AndroidRuntime(1340):     at android.os.Handler.dispatchMessage(Handler.java:95)
08-15 19:23:27.195: E/AndroidRuntime(1340):     at android.os.Looper.loop(Looper.java:136)
08-15 19:23:27.195: E/AndroidRuntime(1340):     at android.app.ActivityThread.main(ActivityThread.java:5017)
08-15 19:23:27.195: E/AndroidRuntime(1340):     at java.lang.reflect.Method.invokeNative(Native Method)
08-15 19:23:27.195: E/AndroidRuntime(1340):     at java.lang.reflect.Method.invoke(Method.java:515)
08-15 19:23:27.195: E/AndroidRuntime(1340):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:779)
08-15 19:23:27.195: E/AndroidRuntime(1340):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:595)
08-15 19:23:27.195: E/AndroidRuntime(1340):     at dalvik.system.NativeStart.main(Native Method)

line 108

        usersListView.setAdapter(namesArrayAdapter);

Updated Activity Code

public class Fragment1 extends Fragment {

    private String currentUserId;
    private ArrayAdapter<String> namesArrayAdapter;
    private ArrayList<String> names;
    private ListView usersListView;
    private Button logoutButton;
    String userGender = ParseUser.getCurrentUser().getString("Gender");
    String activityName = ParseUser.getCurrentUser().getString("ActivityName");
    Number maxDistance = ParseUser.getCurrentUser().getNumber("Maximum_Distance");
    String userLookingGender = ParseUser.getCurrentUser().getString("Looking_Gender");
    Number minimumAge = ParseUser.getCurrentUser().getNumber("Minimum_Age");
    Number maximumAge = ParseUser.getCurrentUser().getNumber("Maximum_Age");
    Number userage = ParseUser.getCurrentUser().getNumber("Age");

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

        setConversationsList();

    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,Bundle savedInstanceState) {
        View view = inflater.inflate(R.layout.fragment1_layout, container, false);


        return view;
    }

private void setConversationsList() {
    currentUserId = ParseUser.getCurrentUser().getObjectId();
    names = new ArrayList<String>();
    // String userActivitySelectionName = null;

    ParseQuery<ParseUser> query = ParseUser.getQuery();

    //  query.whereEqualTo("ActivityName",userActivitySelectionName);

    query.whereNotEqualTo("objectId", ParseUser.getCurrentUser().getObjectId());
    // users with Gender = currentUser.Looking_Gender
    query.whereEqualTo("Gender", userLookingGender);
    // users with Looking_Gender = currentUser.Gender
    query.whereEqualTo("Looking_Gender", userGender);
    query.setLimit(1);
    query.whereEqualTo("ActivityName", activityName);
    query.whereGreaterThanOrEqualTo("Minimum_Age", minimumAge).whereGreaterThanOrEqualTo("Age", userage);
    query.whereLessThanOrEqualTo("Maximum_Age", maximumAge).whereLessThanOrEqualTo("Age", userage);
    //  query.whereWithinKilometers("Maximum_Distance", point, maxDistance)





    query.findInBackground(new FindCallback<ParseUser>() {

        public void done(List<ParseUser> userList, ParseException e) {
            if (e == null) {
                for (int i=0; i<userList.size(); i++) {
                    names.add(userList.get(i).get("Name").toString());
                    names.add(userList.get(i).get("Headline").toString());
                    names.add(userList.get(i).get("Age").toString());

                    //       names.add(userList.get(i).getParseObject("ProfilePicture").;


                }




                usersListView = (ListView)getActivity().findViewById(R.id.usersListView);
                namesArrayAdapter =
                        new ArrayAdapter<String>(getActivity().getApplicationContext(),
                                R.layout.user_list_item, names);
                usersListView.setAdapter(namesArrayAdapter);

                usersListView.setOnItemClickListener(new AdapterView.OnItemClickListener() {
                    @Override
                    public void onItemClick(AdapterView<?> a, View v, int i, long l) {
                        openConversation(names, i);
                    }
                });

            } else {
                Toast.makeText(getActivity().getApplicationContext(),
                        "Error loading user list",
                        Toast.LENGTH_LONG).show();
            }
        }
    });
}

public void openConversation(ArrayList<String> names, int pos) {
    ParseQuery<ParseUser> query = ParseUser.getQuery();
    query.whereEqualTo("Name", names.get(pos));
    query.findInBackground(new FindCallback<ParseUser>() {
        public void done(List<ParseUser> user, ParseException e) {
            if (e == null) {
                Intent intent = new Intent(getActivity().getApplicationContext(), MessagingActivity.class);
                intent.putExtra("RECIPIENT_ID", user.get(0).getObjectId());
                startActivity(intent);
            } else {
                Toast.makeText(getActivity().getApplicationContext(),
                        "Error finding that user",
                        Toast.LENGTH_SHORT).show();
            }
        }
    });
}
}

I am a bit confused, and even with research done, I have difficulty finding, and solving the issues. Kindly advise, Thanks in advance

Answer 1

If the views you are finding in setConversationsList() are from the fragment's layout (R.layout.fragment1_layout), then you must inflate the layout first:

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,Bundle savedInstanceState) {
    View view = inflater.inflate(R.layout.fragment1_layout, container, false);

    setConversationsList();

    return view;
}

Note that using getActivity before onActivityCreated is perfectly normal as it's already available since onAttach. However if the views you are looking for, belong to the activity's layout, then you should be finding them in onActivityCreated.

Answer 2

You might need to check if List<ParseUser> userList is null or not before iterating.

Answer 3

Again, you are calling getActivity() prior to onActivityCreated(), and therefore getActivity() returns null.

onCreateView() is called prior to onActivityCreated(). onActivityCreated() is Called when the activity's onCreate() method has returned. That means that when onCreateView() is called, the fragment's getActivitiy() method would return null.

In onCreateView() you call setConversationsList() which access getActivity() in multiple places. Hence the NullPointerException.