如何在抽屉菜单中获取已登录用户的信息？

huangapple
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英文:

How to get logged user's information in drawer menu?

问题

我试图从 Firebase 中获取当前用户的用户名和电子邮件，并在抽屉菜单中显示出来。然而，程序崩溃并返回了以下错误：

  1. java.lang.NullPointerException: 尝试在空对象引用上调用虚拟方法 'void android.widget.TextView.setText(java.lang.CharSequence)'
  2.         at com.example.android.myapplication.NavigationActivity$1.onDataChange(NavigationActivity.java:79)

以下是我的导航活动代码部分：

  1. public class NavigationActivity extends AppCompatActivity implements NavigationView.OnNavigationItemSelectedListener{
  3.     // ... (其他代码)
  5.     private void getUserInformation() {
  6.         DatabaseReference userDatabase= FirebaseDatabase.getInstance().getReference().child("users").child(userId);
  8.         userDatabase.addValueEventListener(new ValueEventListener() {
  9.             @Override
  10.             public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
  11.                 if (dataSnapshot.exists()) {
  12.                     for (DataSnapshot child : dataSnapshot.getChildren()) {
  13.                         if (child.getKey().equals("name")) {
  14.                             name.setText(child.getValue().toString());
  15.                         }
  16.                         if (child.getKey().equals("email")) {
  17.                             email.setText(child.getValue().toString());
  18.                         }
  19.                     }
  20.                 }
  21.             }
  23.             @Override
  24.             public void onCancelled(@NonNull DatabaseError databaseError) {
  26.             }
  27.         });
  28.     }
  30.     // ... (其他代码)
  31. }

这是我的数据库结构截图：

如何在抽屉菜单中获取已登录用户的信息？

我猜测问题可能是因为 NavigationActivity 不是主要活动，然而，即使我将其更改为主要活动，我仍然遇到相同的错误。

英文:

I've tried to retrieve the current user's username and email from firebase and display it in the drawer menu. However, the program crashed and return the error:

  1. java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.TextView.setText(java.lang.CharSequence)' on a null object reference
  2.         at com.example.android.myapplication.NavigationActivity$1.onDataChange(NavigationActivity.java:79)

Here is my Navigation Activity

  1. public class NavigationActivity extends AppCompatActivity implements NavigationView.OnNavigationItemSelectedListener{
  3.     protected DrawerLayout drawer;
  4.     private String userId;
  5.     private TextView email,name;
  6.     private DatabaseReference mDatabase;
  7.     private FirebaseAuth mAuth;
  9.     @Override
  10.     protected void onCreate(Bundle savedInstanceState) {
  11.         super.onCreate(savedInstanceState);
  12.         setContentView(R.layout.activity_navigation);
  14.         Toolbar toolbar = findViewById(R.id.toolbar);
  15.         setSupportActionBar(toolbar);
  16.         drawer = findViewById(R.id.drawer_layout);
  17.         NavigationView navigationView=findViewById(R.id.nav_view);
  18.         navigationView.setNavigationItemSelectedListener(this);
  20.         ActionBarDrawerToggle toggle = new ActionBarDrawerToggle(this, drawer, toolbar,
  21.                 R.string.navigation_drawer_open, R.string.navigation_drawer_close);
  22.         drawer.addDrawerListener(toggle);
  23.         toggle.syncState();
  25.         name = (TextView)findViewById(R.id.name);
  26.         email=(TextView)findViewById(R.id.email);
  28.         mAuth=FirebaseAuth.getInstance();
  29.         userId= mAuth.getCurrentUser().getUid();
  31.         getUserInformation();
  33.     }
  35.     private void getUserInformation() {
  36.         DatabaseReference userDatabase= FirebaseDatabase.getInstance().getReference().child("users").child(userId);
  38.         userDatabase.addValueEventListener(new ValueEventListener() {
  39.             @Override
  40.             public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
  41.                 if (dataSnapshot.exists()) {
  42.                     for (DataSnapshot child : dataSnapshot.getChildren()) {
  43.                         if (child.getKey().equals("name")) {//find the child that Equals to start
  44.                             name.setText(child.getValue().toString());
  45.                         }
  46.                         if (child.getKey().equals("email")) {//find the child that Equals to start
  47.                             email.setText(child.getValue().toString());
  48.                         }
  49.                     }
  50.                 }
  51.             }
  53.             @Override
  54.             public void onCancelled(@NonNull DatabaseError databaseError) {
  56.             }
  57.         });
  58.     }
  61.     @Override
  62.     public void onBackPressed() {
  63.         if (drawer.isDrawerOpen(GravityCompat.START)) {
  64.             drawer.closeDrawer(GravityCompat.START);
  65.         } else {
  66.             super.onBackPressed();
  67.         }
  68.     }
  70.     @Override
  71.     public boolean onNavigationItemSelected(@NonNull MenuItem item) {
  72.         switch(item.getItemId()){
  73.             case R.id.nav_run:
  74.                 Intent intent = new Intent(NavigationActivity.this,running_map.class);
  75.                 startActivity(intent);
  76.                 finish();
  77.                 break;
  78.             case R.id.nav_history:
  79.                 Intent intent2 = new Intent(NavigationActivity.this,HistoryActivity.class);
  80.                 startActivity(intent2);
  81.                 finish();
  82.                 break;
  83.             //......
  84.         }
  85.         drawer.closeDrawer(GravityCompat.START);
  86.         return true;
  87.     }
  88. }

Here is my database:
如何在抽屉菜单中获取已登录用户的信息？
I guessed that this is because the NavigationActivity was not the main activity, however, even when I changed it to the main activity, I still got the same error.

答案1

得分: 2

你不需要使用 for 循环：

  1. private void getUserInformation() {
  2.     DatabaseReference userDatabase = FirebaseDatabase.getInstance().getReference().child("users").child(userId);
  4.     userDatabase.addValueEventListener(new ValueEventListener() {
  5.         @Override
  6.         public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
  7.             if (dataSnapshot.exists()) {
  8.                 if (dataSnapshot.child("name").getValue(String.class).equals("name")) {
  9.                     name.setText(child.getValue().toString());
  10.                 }
  11.                 if (dataSnapshot.child("email").getValue(String.class).equals("email")) {
  12.                     email.setText(child.getValue().toString());
  13.                 }
  14.             }
  15.         }
  17.         @Override
  18.         public void onCancelled(@NonNull DatabaseError databaseError) {
  20.         }
  21.     });
  22. }

你的引用位于节点 userId，因此要获取详细信息，你不需要进行迭代。

英文:

You dont need the for loop:

  1.     private void getUserInformation() {
  2.         DatabaseReference userDatabase= FirebaseDatabase.getInstance().getReference().child("users").child(userId);
  4.         userDatabase.addValueEventListener(new ValueEventListener() {
  5.             @Override
  6.             public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
  7.                 if (dataSnapshot.exists()) {
  8.                         if (dataSnapshot.child("name").getValue(String.class).equals("name")) {//find the child that Equals to start
  9.                             name.setText(child.getValue().toString());
  10.                         }
  11.                         if (dataSnapshot.child("email").getValue(String.class).equals("email")) {//find the child that Equals to start
  12.                             email.setText(child.getValue().toString());
  13.                         }
  14.                     }
  15.             }
  17.             @Override
  18.             public void onCancelled(@NonNull DatabaseError databaseError) {
  20.             }
  21.         });
  22.     }

Your reference is at node userId, therefore to get the details you dont need to iterate.

huangapple
  • 本文由 发表于 2020年3月16日 05:49:40
  • 转载请务必保留本文链接：https://go.coder-hub.com/60698009.html
  • android
  • firebase
  • firebase-realtime-database
  • java
  • navigation-drawer
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