Question

当我尝试运行应用程序时，它会自动崩溃并显示错误

由于：java.lang.NullPointerException：尝试调用虚拟方法'java.lang.String com.google.firebase.auth.FirebaseUser.getUid（）”在空对象上参考在com.example.akhilkumar.chitchat.MainActivity.onCreate（MainActivity.java:55）

指向

的错误

currentUserID = mAuth.getCurrentUser（）。getUid（）;

public class MainActivity extends AppCompatActivity {

    private NavigationView navigationView;
    private DrawerLayout drawerLayout;
    private RecyclerView postList;
    private Toolbar mToolbar;
    private ActionBarDrawerToggle actionBarDrawerToggle;

    private FirebaseAuth mAuth;

    private DatabaseReference userRef;

    private CircleImageView navProfileImage;
    private TextView navProfileUserName;

    String currentUserID;

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



        mAuth = FirebaseAuth.getInstance();


        currentUserID = mAuth.getCurrentUser().getUid();

        userRef = FirebaseDatabase.getInstance().getReference().child("Users");

/*
        mToolbar = (Toolbar)findViewById(R.id.main_page_toolbar);
        setSupportActionBar(mToolbar);
*/
        getSupportActionBar().setTitle("Home");

        drawerLayout = (DrawerLayout)findViewById(R.id.drawable_layout);
        actionBarDrawerToggle = new ActionBarDrawerToggle(MainActivity.this, drawerLayout, R.string.drawer_open, R.string.drawer_close);
        drawerLayout.addDrawerListener(actionBarDrawerToggle);
        actionBarDrawerToggle.syncState();
        getSupportActionBar().setDisplayHomeAsUpEnabled(true);


        navigationView = (NavigationView)findViewById(R.id.navigation_view);

        View navView = navigationView.inflateHeaderView(R.layout.navigation_header);

        navProfileImage = (CircleImageView)navView.findViewById(R.id.nav_profile_image);
        navProfileUserName =(TextView)navView.findViewById(R.id.nav_user_full_name);



        userRef.child(currentUserID).addValueEventListener(new ValueEventListener() {
            @Override
            public void onDataChange(DataSnapshot dataSnapshot)
            {
                if(dataSnapshot.exists())
                {
                    if(dataSnapshot.hasChild("fullname"))
                    {
                        String fullname = dataSnapshot.child("fullname").getValue().toString();
                        navProfileUserName.setText(fullname);
                    }
                    if(dataSnapshot.hasChild("profileimage"))
                    {
                        String image = dataSnapshot.child("profileimage").getValue().toString();
                        Picasso.get().load(image).placeholder(R.drawable.profile).into(navProfileImage);
                    }
                    else
                    {
                        Toast.makeText(MainActivity.this, "Profile name do not exists...", Toast.LENGTH_SHORT).show();
                    }
                }
            }

            @Override
            public void onCancelled(DatabaseError databaseError) {

            }
        });



        navigationView.setNavigationItemSelectedListener(new NavigationView.OnNavigationItemSelectedListener() {
            @Override
            public boolean onNavigationItemSelected(@NonNull MenuItem item) {

                UserMenuSelector(item);


                return false;
            }
        });

    }





    @Override
    protected void onStart() {
        super.onStart();
        FirebaseUser currentUser = mAuth.getCurrentUser();

        if(currentUser == null){
            SendUserToLoginActivity();
        }
        else{
            CheckUserExistence();
        }
    }

    private void CheckUserExistence() {

        final String current_user_id = mAuth.getCurrentUser().getUid();

        userRef.addValueEventListener(new ValueEventListener() {
            @Override
            public void onDataChange(DataSnapshot dataSnapshot)
            {
                if(!dataSnapshot.hasChild(current_user_id))
                {
                    SendUserToSetupActivity();
                }
            }

            @Override
            public void onCancelled(DatabaseError databaseError) {

            }
        });

    }

    private void SendUserToSetupActivity() {

        Intent setupIntent = new Intent(MainActivity.this, SetupActivity.class);
        setupIntent.addFlags(Intent.FLAG_ACTIVITY_NEW_TASK | Intent.FLAG_ACTIVITY_CLEAR_TASK);
        startActivity(setupIntent);
        finish();

    }

    private void SendUserToLoginActivity() {

        Intent loginIntenet = new Intent(MainActivity.this, LoginActivity.class);
        loginIntenet.addFlags(Intent.FLAG_ACTIVITY_NEW_TASK | Intent.FLAG_ACTIVITY_CLEAR_TASK);
        startActivity(loginIntenet);
        finish();

    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {

        if(actionBarDrawerToggle.onOptionsItemSelected(item)){
            return true;
        }
        return super.onOptionsItemSelected(item);
    }

    private void UserMenuSelector(MenuItem item) {

        switch (item.getItemId()){


            case R.id.nav_profile:
                Toast.makeText(this,"Profile",Toast.LENGTH_LONG).show();
                break;
            case R.id.nav_home:
                Toast.makeText(this,"Home",Toast.LENGTH_LONG).show();
                break;

            case R.id.nav_friends:
                Toast.makeText(this,"Friends",Toast.LENGTH_LONG).show();
                break;

            case R.id.nav_find_friends:
                Toast.makeText(this,"Find Friends",Toast.LENGTH_LONG).show();
                break;

            case R.id.nav_messages:
                Toast.makeText(this,"Messages",Toast.LENGTH_LONG).show();
                break;

            case R.id.nav_settings:
                Toast.makeText(this,"Settings",Toast.LENGTH_LONG).show();
                break;

            case R.id.nav_logout:

                mAuth.signOut();
                SendUserToLoginActivity();
                Toast.makeText(this,"Logout Successfully",Toast.LENGTH_LONG).show();
                break;

            case R.id.nav_about_app:
                Toast.makeText(this,"About",Toast.LENGTH_LONG).show();
                break;





        }
    }
}

Answer 1

下面的代码行：

currentUserID = mAuth.getCurrentUser().getUid();

可能产生NullPointerException。因此，要解决此问题，您需要首先检查无效性。因此，请使用以下代码行：

FirebaseUser mFirebaseUser = mAuth.getCurrentUser();
if(mFirebaseUser != null) {
    currentUserID = mFirebaseUser.getUid(); //Do what you need to do with the id
}

Answer 2

您正在onStart方法中访问mAuth，但正在onCreate中对其进行了初始化。因此，这就是您收到此错误的原因。

因此，请在onCreate（）方法中编写以下代码

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

    mAuth = FirebaseAuth.getInstance();

    FirebaseUser currentUser = mAuth.getCurrentUser();

    if(currentUser == null){
        SendUserToLoginActivity();
    }
    else{
        CheckUserExistence();
    }
}

空对象引用上的java.lang.String com.google.firebase.auth.FirebaseUser.getUid（）'

2 个答案: