参数'pathString'为null

Question

在Firebase中执行查询时出现错误，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：

异常java.lang.RuntimeException：无法启动活动ComponentInfo {ucarparceiro.ucarapp.com.ucarparceiro / ucarparceiro.ucarapp.com.ucarparceiro.Activity.ActivityPrincipal.ActivityPerfil}：java.lang.NullPointerException：无法为参数'传递null child（）中的pathString' 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：

用户 员工

Answer 1

您很可能会收到错误消息，因为cpf在将其作为子级使用时为null mReferenceplaca。发生这种情况是因为Firebase异步下载数据，并且您的代码行是同步执行的。因此，在mReferencePlaca.child("Funcionario").child(cpf).child("placa")执行此行时，的值cpf仍为null，因为这cpf = dataSnapshot.getValue(String.class);尚未发生。

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) {

            }
        });