如何从 Firebase 检索数据以在 TextView 中显示？ [关闭]

Question

我的 firebase 数据库结构如下所示：

我正在使用此代码，但它不会从数据库中检索任何数据，有时getUid() 会产生 NullPointerException。谁能帮我解决这个问题？

mAuth = FirebaseAuth.getInstance();

mUser = mAuth.getCurrentUser();

userID = mUser.getUid();

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

mDatabaseReference.addValueEventListener(new ValueEventListener() {

    @Override
    public void onDataChange(DataSnapshot dataSnapshot) {
        showData(dataSnapshot);
    }

    @Override
    public void onCancelled(DatabaseError databaseError) {

    }
});

private void showData(DataSnapshot dataSnapshot) {
    for (DataSnapshot ds: dataSnapshot.getChildren()) {
        UserInformation uInfo = new UserInformation();
        uInfo.setFullName(ds.child(userID).getValue(UserInformation.class).getFullName());
        uInfo.setUsername(ds.child(userID).getValue(UserInformation.class).getUsername());
        uInfo.setEmail(ds.child(userID).getValue(UserInformation.class).getEmail());
        
        fullNameProfile.setText(uInfo.getFullName());
        usernameProfile.setText(uInfo.getUsername());
        emailProfile.setText(uInfo.getEmail());
    }
}

Answer 1

要简单地从数据库中获取用户数据，请使用以下代码行：

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

DatabaseReference rootRef = FirebaseDatabase.getInstance().getReference();
DatabaseReference uidRef = rootRef.child("Users").child(uid);
ValueEventListener valueEventListener = new ValueEventListener() {
    @Override
    public void onDataChange(DataSnapshot dataSnapshot) {
        String email = dataSnapshot.child("Email").getValue(String.class);
        String fullName = dataSnapshot.child("FullName").getValue(String.class);
        String password = dataSnapshot.child("Password").getValue(String.class);
        String userName = dataSnapshot.child("Username").getValue(String.class);
        Log.d(TAG, userName);
    }

    @Override
    public void onCancelled(@NonNull DatabaseError databaseError) {
        Log.d(TAG, databaseError.getMessage()); //Don't ignore errors!
    }
};
uidRef.addListenerForSingleValueEvent(valueEventListener);

使用UserInformation 类甚至更简单：

DatabaseReference rootRef = FirebaseDatabase.getInstance().getReference();
DatabaseReference uidRef = rootRef.child("Users").child(uid);
ValueEventListener valueEventListener = new ValueEventListener() {
    @Override
    public void onDataChange(DataSnapshot dataSnapshot) {
        UserInformation uInfo = dataSnapshot.getValue(UserInformation.class);
        Log.d(TAG, uInfo.getUsername());
    }

    @Override
    public void onCancelled(@NonNull DatabaseError databaseError) {
        Log.d(TAG, databaseError.getMessage()); //Don't ignore errors!
    }
};
uidRef.addListenerForSingleValueEvent(valueEventListener);