Activity crashing the second time it is launched through intent

Question

I am designing a simple store/retrieve data android app using firebase.

Activity1 is a login activity, that goes straight to Activity2 when a user successfully logs in. There are no problems when logging in the first time, everything is in its proper place. I have a Navigation Drawer in Activity2 which I use to switch fragments, and in that navigation drawer, users can logout and go back to the login activity. Below is an excerpt from Activity2 that takes the user back to the login activity

            case R.id.nav_logout:
            account_key = "";
            Toast.makeText(getApplicationContext(), "Logged Out", Toast.LENGTH_LONG).show();
            Intent intent = new Intent(getApplicationContext(), LoginActivity.class);
            startActivity(intent);
            finish();
            break;

When I click the logout button, it takes me to Activity1 as it should be. Now the problem is when I try to login again, the app just crashes with the following error:

E/AndroidRuntime: FATAL EXCEPTION: main
    Process: com.adzu.bfarsystem, PID: 2143
    java.lang.NullPointerException: Attempt to invoke interface method 'android.view.MenuItem android.view.Menu.add(int, int, int, java.lang.CharSequence)' on a null object reference
        at android.view.MenuInflater$MenuState.addItem(MenuInflater.java:540)
        at android.view.MenuInflater.parseMenu(MenuInflater.java:193)
        at android.view.MenuInflater.inflate(MenuInflater.java:114)
        at androidx.appcompat.view.SupportMenuInflater.inflate(SupportMenuInflater.java:120)
        at com.adzu.bfarmobile.activities.MainActivity.createSearchView(MainActivity.java:153)
        at com.adzu.bfarmobile.activities.MainActivity$1.dataRetrieved(MainActivity.java:109)
        at com.adzu.bfarmobile.entities.DatabaseReader$3.onChildAdded(DatabaseReader.java:64)
        at com.google.firebase.database.core.ChildEventRegistration.fireEvent(ChildEventRegistration.java:79)
        at com.google.firebase.database.core.view.DataEvent.fire(DataEvent.java:63)
        at com.google.firebase.database.core.view.EventRaiser$1.run(EventRaiser.java:55)
        at android.os.Handler.handleCallback(Handler.java:873)
        at android.os.Handler.dispatchMessage(Handler.java:99)
        at android.os.Looper.loop(Looper.java:193)
        at android.app.ActivityThread.main(ActivityThread.java:6669)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:493)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:858)

And here are the lines that triggered the errors:

LoginActivity.java Lines 95-102

               if (activated) {
                    Toast.makeText(getApplicationContext(), "Login Success!", Toast.LENGTH_LONG).show();

                    Intent newIntent = new Intent(getApplicationContext(), MainActivity.class);
                    newIntent.putExtra("account_key", dataSnapshot.getKey());
                    startActivity(newIntent);
                    finish();
                }

MainActivity.java Line 95-127

Intent intent = getIntent();
account_key = intent.getStringExtra("account_key");

DatabaseReference ref = FirebaseDatabase.getInstance().getReference("account");
DatabaseReader.readDataByKey(account_key, ref, new OnGetDataListener() {
    @Override
    public void dataRetrieved(DataSnapshot dataSnapshot) {
        Account user = new Account((Map<String, Object>) dataSnapshot.getValue());
        fragment1 = new ListFragment();
        fragment1.setUser(user);
        createSearchView();
        showSearchView();
        getSupportFragmentManager().beginTransaction().replace(R.id.fragment_container, fragment1).commit();
        navigationView.setCheckedItem(R.id.nav_operatorlist);
        TextView acct_name = findViewById(R.id.acct_name);
        acct_name.setText("Logged in as: " + user.getUsername());
    }

    @Override
    public void dataExists(DataSnapshot dataSnapshot) {

    }

    @Override
    public void onStart() {

    }

    @Override
    public void onFailure() {

    }
});

MainActivity.java Line 141-153

@Override
public boolean onCreateOptionsMenu(Menu menu) {
    this.menu = menu;
    return super.onCreateOptionsMenu(menu);
}

public void createSearchView(){
    MenuInflater inflater = getMenuInflater();
    inflater.inflate(R.menu.search_menu, menu);
    MenuItem searchItem = menu.findItem(R.id.action_search);
    searchView = findViewById(R.id.search_view);
    searchView.setMenuItem(searchItem);
    expandableLayout = findViewById(R.id.expandable_layout);

DatabaseReader.java Line 64-89

    public static void readDataByKey(String account_key, DatabaseReference ref, final OnGetDataListener listener) {
        listener.onStart();
        Query query = ref.orderByKey().equalTo(account_key);
        query.addChildEventListener(new ChildEventListener() {
            @Override
            public void onChildAdded(@NonNull DataSnapshot dataSnapshot, @Nullable String s) {
                listener.dataRetrieved(dataSnapshot);
            }

            @Override
            public void onChildChanged(@NonNull DataSnapshot dataSnapshot, @Nullable String s) {

            }

            @Override
            public void onChildRemoved(@NonNull DataSnapshot dataSnapshot) {

            }

            @Override
            public void onChildMoved(@NonNull DataSnapshot dataSnapshot, @Nullable String s) {

            }

            @Override
            public void onCancelled(@NonNull DatabaseError databaseError) {
                listener.onFailure();
            }
        });

    }

Any help would be greatly appreciated. Thanks!

Answer 1

You may run into a race condition. You may have invoked createSearchView before the system calls onCreateOptionsMenu , so menu is null .

Try to have onCreateOptionsMenu invoke createSearchView after line:

this.menu = menu;