我在 firebase 中执行查询时遇到错误，我的查询代码如下所示:

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

txtNome = (TextView) findViewById(R.id.txtNomePerfil);
txtCpf = (TextView) findViewById(R.id.txtCpfPerfil);
txtEmail = (TextView) findViewById(R.id.txtEmailPerfil);
txtFone = (TextView) findViewById(R.id.txtCelularPerfil);
txtPlaca = (TextView) findViewById(R.id.txtPlacaPerfil);
imgPerfil = (ImageView) findViewById(R.id.imgPerfil);
txtNomeFantasia = (TextView) findViewById(R.id.txtNomeFantasiaPerfil);
txtCnpj = (TextView) findViewById(R.id.txtCnpjPerfil);

firebaseUser = firebaseAuth.getInstance().getCurrentUser();

uId = firebaseUser.getUid();
email = firebaseUser.getEmail();
txtEmail.setText(email);

databaseReference = FirebaseDatabase.getInstance().getReference();

databaseReference.child("Usuario").child(uId).child("nome")
        .addValueEventListener(new ValueEventListener() {
            @Override
            public void onDataChange(DataSnapshot dataSnapshot) {
              nome = dataSnapshot.getValue(String.class);
                txtNome.setText(nome);
            }

            @Override
            public void onCancelled(DatabaseError databaseError) {

            }
        });


  DatabaseReference mReferenceCpf = FirebaseDatabase.getInstance().getReference();
databaseReference.child("Usuario").child(uId).child("cnpjCpf")
        .addValueEventListener(new ValueEventListener() {
            @Override
            public void onDataChange(DataSnapshot dataSnapshot) {
             cpf = dataSnapshot.getValue(String.class);
                txtCpf.setText(cpf);
            }

            @Override
            public void onCancelled(DatabaseError databaseError) {

            }
        });



   DatabaseReference mReferencePlaca = FirebaseDatabase.getInstance().getReference();
    mReferencePlaca.child("Funcionario").child(cpf).child("placa")
            .addValueEventListener(new ValueEventListener() {
                @Override
                public void onDataChange(DataSnapshot dataSnapshot) {
                    placa = dataSnapshot.getValue(String.class);
                    txtPlaca.setText(placa);
                }

                @Override
                public void onCancelled(DatabaseError databaseError) {

                }
            });

但是我收到以下错误:

Exception java.lang.RuntimeException: Unable to start activity ComponentInfo{ucarparceiro.ucarapp.com.ucarparceiro/ucarparceiro.ucarapp.com.ucarparceiro.Activity.ActivityPrincipal.ActivityPerfil}: java.lang.NullPointerException: Can't pass null for argument 'pathString' in child() android.app.ActivityThread.performLaunchActivity (ActivityThread.java:2316) android.app.ActivityThread.handleLaunchActivity (ActivityThread.java:2376) android.app.ActivityThread.access$800 (ActivityThread.java:147) android.app.ActivityThread$H.handleMessage (ActivityThread.java:1281) android.os.Handler.dispatchMessage (Handler.java:102) android.os.Looper.loop (Looper.java:135) android.app.ActivityThread.main (ActivityThread.java:5253) java.lang.reflect.Method.invoke (Method.java) java.lang.reflect.Method.invoke (Method.java:372) com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run (ZygoteInit.java:899) com.android.internal.os.ZygoteInit.main (ZygoteInit.java:694)

Firebase中的数据如下:

User Employee

最佳答案

您很可能会遇到错误，因为当您在 mReferenceplaca 中将它用作子级时，cpf 为 null。发生这种情况是因为 Firebase 异步下载数据而您的代码行是同步执行的。因此，当这行 mReferencePlaca.child("Funcionario").child(cpf).child("placa") 被执行时，cpf 的值仍然是null 因为这个 cpf = dataSnapshot.getValue(String.class); 还没有发生。

要解决这个问题，请更改:-

    DatabaseReference mReferenceCpf = FirebaseDatabase.getInstance().getReference();
databaseReference.child("Usuario").child(uId).child("cnpjCpf")
        .addValueEventListener(new ValueEventListener() {
            @Override
            public void onDataChange(DataSnapshot dataSnapshot) {
             cpf = dataSnapshot.getValue(String.class);
                txtCpf.setText(cpf);
            }

            @Override
            public void onCancelled(DatabaseError databaseError) {

            }
        });



   DatabaseReference mReferencePlaca = FirebaseDatabase.getInstance().getReference();
    mReferencePlaca.child("Funcionario").child(cpf).child("placa")
            .addValueEventListener(new ValueEventListener() {
                @Override
                public void onDataChange(DataSnapshot dataSnapshot) {
                    placa = dataSnapshot.getValue(String.class);
                    txtPlaca.setText(placa);
                }

                @Override
                public void onCancelled(DatabaseError databaseError) {

                }
            });

对此:-

DatabaseReference mReferenceCpf = FirebaseDatabase.getInstance().getReference();
databaseReference.child("Usuario").child(uId).child("cnpjCpf")
        .addValueEventListener(new ValueEventListener() {
            @Override
            public void onDataChange(DataSnapshot dataSnapshot) {
             cpf = dataSnapshot.getValue(String.class);
                txtCpf.setText(cps);

       DatabaseReference mReferencePlaca = FirebaseDatabase.getInstance().getReference();
        mReferencePlaca.child("Funcionario").child(cpf).child("placa")
                .addValueEventListener(new ValueEventListener() {
                    @Override
                    public void onDataChange(DataSnapshot dataSnapshot) {
                        placa = dataSnapshot.getValue(String.class);
                        txtPlaca.setText(placa);
                    }

                    @Override
                    public void onCancelled(DatabaseError databaseError) {

                    }
                });
            }

            @Override
            public void onCancelled(DatabaseError databaseError) {

            }
        });

关于java - 参数 'pathString' 为空，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/45087951/