android - 我无法从 firebase 数据库中提取相应 uid 的数据

Question

这个问题已经有答案了:

Not able to access inner class data from outer class in Android (1 个回答)

What is a NullPointerException, and how do I fix it? (12 个回答)

已关闭 4 年前。

这是我的目录中显示的错误。它在 HomeActivity 的第 89 行显示错误，user.getName() 为 null。我是 Android 新手，所以无法修复此错误。

    E/AndroidRuntime: FATAL EXCEPTION: main
        Process: com.example.android_foodbot, PID: 12641
        java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.android_foodbot/com.example.android_foodbot.HomeActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.String com.example.android_foodbot.AccountActivity.User.getName()' on a null object reference
            at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2416)
            at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2476)
            at android.app.ActivityThread.-wrap11(ActivityThread.java)
            at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1344)
            at android.os.Handler.dispatchMessage(Handler.java:102)
            at android.os.Looper.loop(Looper.java:148)
            at android.app.ActivityThread.main(ActivityThread.java:5417)
            at java.lang.reflect.Method.invoke(Native Method)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)
         Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.String com.example.android_foodbot.AccountActivity.User.getName()' on a null object reference
            at com.example.android_foodbot.HomeActivity.onCreate(HomeActivity.java:89)
            at android.app.Activity.performCreate(Activity.java:6237)
            at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1107)
            at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2369)
            at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2476) 
            at android.app.ActivityThread.-wrap11(ActivityThread.java) 
            at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1344) 
            at android.os.Handler.dispatchMessage(Handler.java:102) 
            at android.os.Looper.loop(Looper.java:148) 
            at android.app.ActivityThread.main(ActivityThread.java:5417) 
            at java.lang.reflect.Method.invoke(Native Method) 
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726) 
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616) 

登录 Activity :

    public class SignUpActivity extends AppCompatActivity {

        private EditText inputName,  inputPhone, inputEmail,  inputPassword;
        private FirebaseAuth auth;
        private Button btnSignUp, btnLogin;

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

            auth = FirebaseAuth.getInstance();

            btnLogin = (Button) findViewById(R.id.btn_for_login);
            btnSignUp = (Button) findViewById(R.id.btn_for_signUp);
            inputName = (EditText) findViewById(R.id.name);
            inputPhone = (EditText) findViewById(R.id.phone);
            inputEmail = (EditText) findViewById(R.id.email);
            inputPassword = (EditText) findViewById(R.id.password);

            btnLogin.setOnClickListener(new View.OnClickListener() {
                @Override
                public void onClick(View v) {

                    finish();
                }
            });

            btnSignUp.setOnClickListener(new View.OnClickListener() {
                @Override
                public void onClick(View v) {

                    final ProgressDialog mDialog = new ProgressDialog(SignUpActivity.this);
                    mDialog.setMessage("Loading... Please wait!");
                    mDialog.show();

                    final String name = inputName.getText().toString().trim();
                    final String phone = inputPhone.getText().toString().trim();
                    final String email = inputEmail.getText().toString().trim();
                    String password = inputPassword.getText().toString().trim();

                    if (TextUtils.isEmpty(name)) {
                        mDialog.dismiss();

                        Toast.makeText(getApplicationContext(), "Enter your name!", Toast.LENGTH_SHORT).show();
                        return;
                    }

                    if (TextUtils.isEmpty(phone)) {
                        mDialog.dismiss();

                        Toast.makeText(getApplicationContext(), "Enter your phone number!", Toast.LENGTH_SHORT).show();
                        return;
                    }

                    if (TextUtils.isEmpty(email)) {
                        mDialog.dismiss();

                        Toast.makeText(getApplicationContext(), "Enter email address!", Toast.LENGTH_SHORT).show();
                        return;
                    }

                    if (TextUtils.isEmpty(password)) {
                        mDialog.dismiss();

                        Toast.makeText(getApplicationContext(), "Enter password!", Toast.LENGTH_SHORT).show();
                        return;
                    }

                    if (password.length() < 6) {
                        mDialog.dismiss();

                        Toast.makeText(getApplicationContext(), "Password too short, enter minimum 6 characters!", Toast.LENGTH_SHORT).show();
                        return;
                    }


                    auth.createUserWithEmailAndPassword( email, password)
                            .addOnCompleteListener(SignUpActivity.this, new OnCompleteListener<AuthResult>() {
                                @Override
                                public void onComplete(@NonNull Task<AuthResult> task) {

                                    if (task.isSuccessful()) {

                                        final User user = new User(
                                                name,
                                                email,
                                                phone
                                        );

                                        FirebaseDatabase.getInstance().getReference("Users")
                                                .child(FirebaseAuth.getInstance().getCurrentUser().getUid())
                                                .setValue(user).addOnCompleteListener(new OnCompleteListener<Void>() {
                                            @Override
                                            public void onComplete(@NonNull Task<Void> task) {
                                                mDialog.dismiss();
                                                if (task.isSuccessful()) {
                                                    mDialog.dismiss();

                                                    startActivity(new Intent(SignUpActivity.this, LoginActivity.class));
                                                    finish();
                                                } else {

                                                }
                                            }
                                        });

                                    } else {
                                        mDialog.dismiss();
                                        Toast.makeText(SignUpActivity.this, "Authentication failed." + task.getException(),
                                                Toast.LENGTH_SHORT).show();

                                    }
                                }
                            });

                }
            });
        }


    }

登录 Activity :

    public class LoginActivity extends AppCompatActivity {

        private EditText inputEmail, inputPassword;
        private FirebaseAuth auth;
        private Button btnSignUp, btnLogin;


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

            auth = FirebaseAuth.getInstance();

            if (auth.getCurrentUser() != null) {
                startActivity(new Intent(LoginActivity.this, HomeActivity.class));
                finish();
            }

            setContentView(R.layout.activity_login);
            inputEmail = (EditText) findViewById(R.id.email);
            inputPassword = (EditText) findViewById(R.id.password);
            btnLogin = (Button) findViewById(R.id.btn_login);
            btnSignUp = (Button) findViewById(R.id.btn_signUp);


            auth = FirebaseAuth.getInstance();

            btnSignUp.setOnClickListener(new View.OnClickListener() {
                @Override
                public void onClick(View v) {

                    startActivity(new Intent(LoginActivity.this, SignUpActivity.class));
                }
            });


            btnLogin.setOnClickListener(new View.OnClickListener() {
                @Override
                public void onClick(View v) {

                    final ProgressDialog mDialog = new ProgressDialog(LoginActivity.this);
                    mDialog.setMessage("Loading... Please wait!");
                    mDialog.show();

                    String email = inputEmail.getText().toString();
                    final String password = inputPassword.getText().toString();

                    if (TextUtils.isEmpty(email)) {
                        mDialog.dismiss();

                        Toast.makeText(getApplicationContext(), "Enter email address!", Toast.LENGTH_SHORT).show();
                        return;
                    }

                    if (TextUtils.isEmpty(password)) {
                        mDialog.dismiss();

                        Toast.makeText(getApplicationContext(), "Enter password!", Toast.LENGTH_SHORT).show();
                        return;
                    }


                    auth.signInWithEmailAndPassword(email, password)
                            .addOnCompleteListener(LoginActivity.this, new OnCompleteListener<AuthResult>() {
                                @Override
                                public void onComplete(@NonNull Task<AuthResult> task) {
                                    if (!task.isSuccessful()) {

                                        if (password.length() < 6) {
                                            inputPassword.setError(getString(R.string.minimum_password));
                                        } else {
                                            Toast.makeText(LoginActivity.this, getString(R.string.auth_failed), Toast.LENGTH_LONG).show();
                                        }
                                    } else {
                                        mDialog.dismiss();

                                        FirebaseDatabase database = FirebaseDatabase.getInstance();
                                            String uid = FirebaseAuth.getInstance().getCurrentUser().getUid();
                                            FirebaseDatabase.getInstance().getReference(uid).addListenerForSingleValueEvent(new ValueEventListener() {
                                                @Override
                                                public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
                                                    User user = dataSnapshot.child("name").getValue(User.class);
                                                    Intent intent = new Intent(LoginActivity.this, HomeActivity.class);
                                                    Common.currentUser = user;
                                                    startActivity(intent);
                                                    finish();
                                                }

                                                @Override
                                                public void onCancelled(@NonNull DatabaseError databaseError) {
                                                    throw databaseError.toException();

                                                }
                                            });


                                    }
                                }
                            });


                }
            });
        }
    }

User 类具有三个参数及其构造函数和 getter setter:

    public String name, email, phone;

Nav_header_home 布局，其中必须显示用户详细信息:

    <TextView
        android:id="@+id/textUserName"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:paddingTop="@dimen/nav_header_vertical_spacing"
        android:text="@string/username"
         android:textColor="#ffffff"
        android:textAppearance="@style/TextAppearance.AppCompat.Body1" />

家庭 Activity :

public class HomeActivity extends AppCompatActivity
        implements NavigationView.OnNavigationItemSelectedListener {


    RecyclerView recycler_menu;
    RecyclerView.LayoutManager layoutManager;


    FirebaseDatabase database;
    DatabaseReference category;
    FirebaseRecyclerAdapter<Category, MenuViewHolder> adapter;

    TextView txtUserName;


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


        Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
        toolbar.setTitle("Menu");
        setSupportActionBar(toolbar);

                //        Init Firebase
        database = FirebaseDatabase.getInstance();
        category = database.getReference("Category");

        FloatingActionButton fab = (FloatingActionButton) findViewById(R.id.fab);
        fab.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                Intent cartIntent = new Intent(HomeActivity.this, CartActivity.class);
                startActivity(cartIntent);
//                Snackbar.make(view, "Replace with your own action", Snackbar.LENGTH_LONG)
//                        .setAction("Action", null).show();
            }
        });

        DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
        ActionBarDrawerToggle toggle = new ActionBarDrawerToggle(
                this, drawer, toolbar, R.string.navigation_drawer_open, R.string.navigation_drawer_close);
        drawer.addDrawerListener(toggle);
        toggle.syncState();

        NavigationView navigationView = (NavigationView) findViewById(R.id.nav_view);
        navigationView.setNavigationItemSelectedListener(this);

        FirebaseDatabase database = FirebaseDatabase.getInstance();
        String uid = FirebaseAuth.getInstance().getCurrentUser().getUid();


        FirebaseDatabase.getInstance().getReference().child("User").child(uid).addListenerForSingleValueEvent(new ValueEventListener() {
            @Override
            public void onDataChange(@NonNull DataSnapshot dataSnapshot) {

                Common.currentUser = dataSnapshot.getValue(User.class);
            }

            @Override
            public void onCancelled(@NonNull DatabaseError databaseError) {
                throw databaseError.toException();

            }
        });

        //        Set Name for User
        View headerView = navigationView.getHeaderView(0);
        txtUserName = (TextView)findViewById(R.id.textUserName);
        txtUserName.setText(Common.currentUser.getName());

//      Loading menu
        recycler_menu = findViewById(R.id.recycler_menu);
        RecyclerView.LayoutManager layoutManager = new GridLayoutManager(this, 2);
        recycler_menu.setLayoutManager(layoutManager);
      recycler_menu.addItemDecoration(new GridSpacingItemDecoration(2, dpToPx(10), true));

    }

       /**
     * RecyclerView item decoration - give equal margin around grid item
     */
    public class GridSpacingItemDecoration extends RecyclerView.ItemDecoration {

        private int spanCount;
        private int spacing;
        private boolean includeEdge;

        public GridSpacingItemDecoration(int spanCount, int spacing, boolean includeEdge) {
            this.spanCount = spanCount;
            this.spacing = spacing;
            this.includeEdge = includeEdge;
        }

        @Override
        public void getItemOffsets(Rect outRect, View view, RecyclerView parent, RecyclerView.State state) {
            int position = parent.getChildAdapterPosition(view); // item position
            int column = position % spanCount; // item column

            if (includeEdge) {
                outRect.left = spacing - column * spacing / spanCount; // spacing - column * ((1f / spanCount) * spacing)
                outRect.right = (column + 1) * spacing / spanCount; // (column + 1) * ((1f / spanCount) * spacing)

                if (position < spanCount) { // top edge
                    outRect.top = spacing;
                }
                outRect.bottom = spacing; // item bottom
            } else {
                outRect.left = column * spacing / spanCount; // column * ((1f / spanCount) * spacing)
                outRect.right = spacing - (column + 1) * spacing / spanCount; // spacing - (column + 1) * ((1f /    spanCount) * spacing)
                if (position >= spanCount) {
                    outRect.top = spacing; // item top
                }
            }
        }
    }

    /**
     * Converting dp to pixel
     */
    private int dpToPx(int dp) {
        Resources r = getResources();
        return Math.round(TypedValue.applyDimension(TypedValue.COMPLEX_UNIT_DIP, dp, r.getDisplayMetrics()));
    }


    @Override
    public void onBackPressed() {
        DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
        if (drawer.isDrawerOpen(GravityCompat.START)) {
            drawer.closeDrawer(GravityCompat.START);
        } else {
            super.onBackPressed();
        }
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.home, menu);
        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {

        switch (item.getItemId()){
            case R.id.logout:
                FirebaseAuth.getInstance().signOut();
                finish();
                startActivity(new Intent(this, LoginActivity.class));
                break;
        }

        return true;

//        return super.onOptionsItemSelected(item);
    }

    @SuppressWarnings("StatementWithEmptyBody")
    @Override
    public boolean onNavigationItemSelected(MenuItem item) {
        // Handle navigation view item clicks here.
        int id = item.getItemId();

        if (id == R.id.nav_menu) {
            // Handle the camera action
        } else if (id == R.id.nav_orders) {

        } else if (id == R.id.nav_cart) {

        } else if (id == R.id.nav_logout) {

        }

        DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
        drawer.closeDrawer(GravityCompat.START);
        return true;
    }

    @Override
    protected void onResume() {
        super.onResume();
//        loadMenu();

        adapter = new FirebaseRecyclerAdapter<Category, MenuViewHolder>(Category.class,
                R.layout.menu_item,
                MenuViewHolder.class,
                category) {
            @Override
            protected void populateViewHolder(MenuViewHolder viewHolder, Category model, int position) {
                viewHolder.txtMenuName1.setText(model.getName1());
//                viewHolder.txtMenuPrice1.setText(model.getPrice1());
                Picasso.with(getBaseContext()).load(model.getImage1())
                        .into(viewHolder.imageView1);

                final Category clickItem = model;
                viewHolder.setItemClickListener(new ItemClickListener() {
                    @Override
                    public void onClick(View view, int position, boolean isLongClick) {
//
                        // Get Category id and Start new activity
                        Intent foodList = new Intent(HomeActivity.this, 

    FoodListActivity.class);
                            foodList.putExtra("CategoryId", adapter.getRef(position).getKey());
                            startActivity(foodList);

                        }
                    });

                }
            };
            recycler_menu.setAdapter(adapter);
        }
    }

Answer 1

我想问题就出在这里。 用户 user = dataSnapshot.child("name").getValue(User.class);

情况 1:如果您只需要用户名，则应为: String name = dataSnapshot.child("name").getValue(String.class);

情况 2:如果您需要整个用户对象，则应该是: 用户 user = dataSnapshot.getValue(User.class);

因为您的引用指向字符串对象，而不是用户对象。

据我从您的代码(Common.currentUser = user)中了解到，您可能需要直接用户对象。(情况2)