java – 参数’pathString’为null

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

解决方法:

您最有可能收到错误,因为当您在mReferenceplaca中将其用作子项时,cpf为null.这是因为Firebase异步下载数据并且您的代码行是同步执行的.因此,当执行此行mReferencePlaca.child(“Funcionario”).child(cpf).child(“placa”)时,cpf的值仍然为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) {

            }
        });