Whenever I Open App And Login It Works Fine And Also I Can Easily Logout From App And It Sends Me Back To Login Activity.. But When I Close The App After Login And Reopen App And Then I Logout It Sends Me To Login Activity Then App Closed. Don't Know Why.

Here's The Screenshot of Logcat

Here's The Code Which Causes Problem SignupTabFragment.java

if(firebaseAuth.getCurrentUser() != null){
    // Retrieving User Data From Firebase
    userIDFireStore = firebaseAuth.getCurrentUser().getUid();
    DocumentReference documentReference = firestore.collection("users").document(userIDFireStore);
    documentReference.addSnapshotListener(new EventListener<DocumentSnapshot>() {
        @Override
        public void onEvent(@Nullable DocumentSnapshot value, @Nullable FirebaseFirestoreException error) {
            userTypeFirestore = value.getString("userType");
            if(userTypeFirestore.equals("Admin")){
                startActivity(new Intent(getActivity().getApplicationContext(),AdminHomeActivity.class));
                getActivity().finish();
            }
            if(userTypeFirestore.equals("Student")){
                startActivity(new Intent(getActivity().getApplicationContext(),HomeActivity.class));
                getActivity().finish();
            }
        }
    });
}

HomeActivity.java

public class HomeActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_home);
    }

    public void onLogoutClick(View view) {
        // Logout
            FirebaseAuth.getInstance().signOut();
            startActivity(new Intent(getApplicationContext(),LoginActivity.class));
            finish();
    }

    @Override
    public boolean onKeyDown(int keyCode, KeyEvent event) {
        if(keyCode == KeyEvent.KEYCODE_BACK && event.getRepeatCount() == 0){
            finish();
            System.exit(0);
        }
        return super.onKeyDown(keyCode, event);
    }
}

LoginActivity.java

public class LoginActivity extends AppCompatActivity {

TabLayout tabLayout;
TabItem tabLogin,tabSignup;
ViewPager viewPager;
int nightModeFlags;
ConstraintLayout constraintLayout;


@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_login);

    tabLayout = (TabLayout) findViewById(R.id.tab_layout);
    tabLogin = (TabItem) findViewById(R.id.tab_login);
    tabSignup = (TabItem) findViewById(R.id.tab_signup);
    viewPager = (ViewPager) findViewById(R.id.view_pager);
    constraintLayout = (ConstraintLayout) findViewById(R.id.constraint_backgrond);

    // To Change Constraint Layout Background in Night Mode
    nightModeFlags = constraintLayout.getContext().getResources().getConfiguration().uiMode & Configuration.UI_MODE_NIGHT_MASK;
    switch(nightModeFlags){
        case Configuration.UI_MODE_NIGHT_YES:
            constraintLayout.setBackgroundResource(R.drawable.view_bg_night);
            break;
        case Configuration.UI_MODE_NIGHT_NO:
            constraintLayout.setBackgroundResource(R.drawable.view_bg);
            break;
        case Configuration.UI_MODE_NIGHT_UNDEFINED:
            constraintLayout.setBackgroundResource(R.drawable.view_bg);
            break;
    }


//        tabLayout.addTab(tabLayout.newTab().setText("Login"));
//        tabLayout.addTab(tabLayout.newTab().setText("Sign Up"));
          tabLayout.setTabGravity(TabLayout.GRAVITY_FILL);

    final LoginAdapter adapter = new LoginAdapter(getSupportFragmentManager(), this,tabLayout.getTabCount());
    viewPager.setAdapter(adapter);
    viewPager.addOnPageChangeListener(new TabLayout.TabLayoutOnPageChangeListener(tabLayout));

    // Changing Fragments When The Tab is Selected or Clicked.
    tabLayout.addOnTabSelectedListener(new TabLayout.OnTabSelectedListener() {
        @Override
        public void onTabSelected(TabLayout.Tab tab) {
            viewPager.setCurrentItem(tab.getPosition());
        }

        @Override
        public void onTabUnselected(TabLayout.Tab tab) {

        }

CodePudding user response：

Most likely your security rules require that the user is signed in before they can read their own document from /users/$uid. When you log the user out, that condition is no longer met - so your onEvent is called with an error.

The first problem to fix is to handle the error that is passed to onEvent. The onEvent always gets called with either a DocumentSnapshot or an error, and you need to handle both cases. For example:

public void onEvent(@Nullable DocumentSnapshot value, @Nullable FirebaseFirestoreException error) {
  if (error == null) {
    userTypeFirestore = value.getString("userType");
    if(userTypeFirestore.equals("Admin")){
        startActivity(new Intent(getActivity().getApplicationContext(),AdminHomeActivity.class));
        getActivity().finish();
    }
    if(userTypeFirestore.equals("Student")){
        startActivity(new Intent(getActivity().getApplicationContext(),HomeActivity.class));
        getActivity().finish();
    }
  }
  else {
    Log.e("Firestore", "Error listening to user data", error);
  }
}

To prevent this error from occurring in the first place, you'll want to remove the listener before you log the user out.