I can't retrieve data from Firebase database by user input to TextView

Anyone help me please. I don't understand what I should to do to solve my problem.

I am not able to retrieve data from Firebase database. I am using Java language in android studio. I want to showing "Kode barang" which in database is "kode" and "Harga Barang" which in database is "harga". All of them will show by user input "Nama barang" which in database is "nama".

Screenshot form

If I'm trying to input data in "Nama barang" which is the same as data value in "nama" in database and after that I'm input "jumlah beli" (in english: quantity) and then click "Cek" (english: check"), my app get forced close.

My database structure

This is fragment class

    public class TransPenjFragment extends Fragment {
TextView autotgl;
TextView tvkdbrg;
TextView tvhrgbrg;
TextView totalpj;
EditText edtTextnamabrg;
EditText edtTextjmlbeli;
Button btnCek, btnProses, btnHapus;
private FirebaseDatabase firedb;
private DatabaseReference myRef;
private ArrayList<BarangDB> daftarbarang;
private PenjualanAdapter adapter;
private TabLayout tabLayout;
private ViewPager viewPager;
private ValueEventListener valueEventListener;
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
View view = inflater.inflate(R.layout.fragment_trans_penj, container, false);
tabLayout = view.findViewById(R.id.tabLayout);
viewPager = view.findViewById(R.id.viewPager);
autotgl = view.findViewById(R.id.autotgl);
tvkdbrg = view.findViewById(R.id.tvkdbrg);
tvhrgbrg = view.findViewById(R.id.tvhrgbrg);
totalpj = view.findViewById(R.id.total);
edtTextnamabrg = view.findViewById(R.id.edtTextnamabrg);
edtTextjmlbeli = view.findViewById(R.id.edtTextjmlbeli);
btnCek = view.findViewById(R.id.btnCek);
btnProses = view.findViewById(R.id.btnProses);
btnHapus = view.findViewById(R.id.btnHapus);
FirebaseApp.initializeApp(getActivity());
firedb = FirebaseDatabase.getInstance();
myRef = firedb.getReference();
btnCek.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
final String namabrg = edtTextnamabrg.getText().toString().trim();
myRef = firedb.getInstance().getReference().child("Barang");
Query check = myRef.orderByChild("nama").equalTo(namabrg);
check.addValueEventListener(new ValueEventListener() {
@Override
public void onDataChange(@NonNull DataSnapshot snapshot) {
if(snapshot.exists()){
BarangDB barang = snapshot.getValue(BarangDB.class);
String namabrgfromDB = snapshot.child(namabrg).child("nama").getValue(String.class);
if(namabrgfromDB.equals(namabrg)){
tvkdbrg.setText(barang.getKode());
tvhrgbrg.setText(barang.getHarga());
}else{
Snackbar.make(btnCek, "Barang yang dimasukkan tidak ada di daftar barang",
Snackbar.LENGTH_LONG).show();
}
}else{
Snackbar.make(btnCek, "Tidak tersedia",
Snackbar.LENGTH_LONG).show();
}
}
@Override
public void onCancelled(@NonNull DatabaseError error) {
Toast.makeText(getActivity(), error.getDetails() + " "
+ error.getMessage(), Toast.LENGTH_LONG).show();
}
});
String jmlbeli = edtTextjmlbeli.getText().toString().trim();
double jb =Double.parseDouble(jmlbeli);
double hb = Double.parseDouble(tvhrgbrg.getText().toString());
double total = (jb*hb);
totalpj.setText(" "+total);
}
});

edtTextnamabrg is editText to input "Nama barang" from user to be the same as "nama" in database.

tvkdbrg is textView to retrieve data "Kode Barang" or "kode" from database.

tvhrgbrg is textView to retrieve data "Harga barang" or "harga" from database.

This is my database model

    public class BarangDB implements Serializable {
private String kode;
private String nama;
private String harga;
private String stok;
private String key;
public BarangDB(){ }
public BarangDB (String kode, String nama, String harga, String stok){
this.kode = kode;
this.nama = nama;
this.harga = harga;
this.stok = stok;
}
public String getKey() { return key;}
public void setKey(String key) { this.key = key; }
public String getKode() { return kode;}
public void setKode(String kode) { this.kode = kode; }
public String getNama() { return nama; }
public void setNama(String nama) { this.nama = nama; }
public String getHarga() { return harga; }
public void setHarga(String harga) { this.harga = harga; }
public String getStok() { return stok; }
public void setStok(String stok) { this.stok = stok; }
@Override
public String toString() {
return " "+kode+"\n" + " "+nama+"\n" + " "+harga+ "\n" + " "+stok;
}
}

Logcat

    2020-07-25 23:07:30.250 20490-20490/com.example.aplikasiskripsi E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.example.aplikasiskripsi, PID: 20490
java.lang.NumberFormatException: empty String
at sun.misc.FloatingDecimal.readJavaFormatString(FloatingDecimal.java:1842)
at sun.misc.FloatingDecimal.parseDouble(FloatingDecimal.java:110)
at java.lang.Double.parseDouble(Double.java:538)
at com.example.aplikasiskripsi.TransPenjFragment$1.onClick(TransPenjFragment.java:120)
at android.view.View.performClick(View.java:6605)
at android.view.View.performClickInternal(View.java:6582)
at android.view.View.access$3100(View.java:778)
at android.view.View$PerformClick.run(View.java:25897)
at android.os.Handler.handleCallback(Handler.java:873)
at android.os.Handler.dispatchMessage(Handler.java:99)
at android.os.Looper.loop(Looper.java:193)
at android.app.ActivityThread.main(ActivityThread.java:6762)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:493)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:858)

You are trying to extract a child under Barang key which has key-value pair nama: {value of namabrg}. Note that the result in snapshot does not match your BarangDB class structure. snapshot will return you the next structure:

It means that your BarangDB class must hold another variable of type Energen, which will hold other variables (mode, harga, nama, stok).

And I see you partially understand that and almost got it right.

You need to change two lines. From this:

BarangDB barang = snapshot.getValue(BarangDB.class);
String namabrgfromDB = snapshot.child(namabrg).child("nama").getValue(String.class);

To this:

BarangDB barang = snapshot.child(namabrg).getValue(BarangDB.class);
String namabrgfromDB = barang.getNama();

And it should be enough.