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androiddatabasefirebasefirebase-realtime-databasebarcode-scanner

Cannot retrieve and store student name and student number

I am planning to retrieve the student userName and userStudNum in (User) database and store it in (StoreInfo) database. But it gives me null value. Help me Fix it

StoreInfo:

StoreInfo Database

User:

User database

I have 2 java file. scanner.java

this scanner.java will setText for textview when qr are scanned. But just like in firebase, it store null value.

public class scanner extends Drawable {
    Button qrbtn;
    public static FusedLocationProviderClient fusedLocationProviderClient;
    public static TextView qrtext, id, arrival, date, address, name, studNum;
    public static int REQUEST_CODE = 100;
    private FirebaseUser currentUser;
    DatabaseReference usersRef;
    ActivityScannerBinding activityScannerBinding;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        activityScannerBinding = ActivityScannerBinding.inflate(getLayoutInflater());
        setContentView(activityScannerBinding.getRoot());
        allocateActivityTitle("Attendance Scanner");

        qrbtn = (Button) findViewById(R.id.qrbtn);
        qrtext = (TextView) findViewById(R.id.qrtext);
        arrival = (TextView) findViewById(R.id.arrival);
        date = (TextView) findViewById(R.id.date);
        id = (TextView) findViewById(R.id.deviceId);
        name = (TextView) findViewById(R.id.name);
        studNum = (TextView) findViewById(R.id.studentNum);
        address = (TextView) findViewById(R.id.location);


        fusedLocationProviderClient = LocationServices.getFusedLocationProviderClient(this);
        // saveUser();

        qrbtn.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                startActivity(new Intent(getApplicationContext(), qrscanner.class));
                getLocation();
                saveUser();
            }
        });
    }

    private void getLocation() {
        if (ContextCompat.checkSelfPermission(this, Manifest.permission.ACCESS_FINE_LOCATION) == PackageManager.PERMISSION_GRANTED) {
            fusedLocationProviderClient.getLastLocation().addOnSuccessListener(new OnSuccessListener<Location>() {
                @Override
                public void onSuccess(Location location) {

                    if (location != null) {
                        try {
                            Geocoder geocoder = new Geocoder(scanner.this, Locale.getDefault());

                            List<Address> addresses = geocoder.getFromLocation(location.getLatitude(), location.getLongitude(), 1);
                            address.setText("Location: " + addresses.get(0).getAddressLine(0)
                            );
                        } catch (IOException e) {

                            e.printStackTrace();
                        }
                    }
                }
            });
        } else {
            askPermission();
        }
    }

    private void askPermission() {
        ActivityCompat.requestPermissions(scanner.this, new String[]{Manifest.permission.ACCESS_FINE_LOCATION}, REQUEST_CODE);
    }

    @Override
    public void onRequestPermissionsResult(int requestCode, @NonNull @org.jetbrains.annotations.NotNull String[] permissions, @NonNull @org.jetbrains.annotations.NotNull int[] grantResults) {

        if (requestCode == REQUEST_CODE) {

            if (grantResults.length > 0 && grantResults[0] == PackageManager.PERMISSION_GRANTED) {
                getLocation();
            } else {
                Toast.makeText(scanner.this, "Please provide the required permission", Toast.LENGTH_SHORT).show();
            }
        }

        super.onRequestPermissionsResult(requestCode, permissions, grantResults);
    }

    private void saveUser() {
        DatabaseReference ref = FirebaseDatabase.getInstance().getReference("User");
        FirebaseAuth auth = FirebaseAuth.getInstance();
        FirebaseUser user = auth.getCurrentUser();

        ref.addListenerForSingleValueEvent(new ValueEventListener() {
            @Override
            public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
                String nameString = dataSnapshot.child("userName").getValue(String.class);
                String studNumString = dataSnapshot.child("userStudNo").getValue(String.class);

                name.setText("" + nameString);
                studNum.setText("" + studNumString);
            }

            @Override
            public void onCancelled(@NonNull DatabaseError databaseError) {
            }
        });
    }
}

qrscanner.java

public class qrscanner extends Drawable implements ZXingScannerView.ResultHandler
{
    ZXingScannerView scannerView;
    DatabaseReference dbref, usersRef;
    private FirebaseUser currentUser;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        scannerView = new ZXingScannerView(this);
        setContentView(scannerView);
        //saveUser();

        dbref = FirebaseDatabase.getInstance().getReference("StoreInfo");
        currentUser = FirebaseAuth.getInstance().getCurrentUser();
        usersRef = FirebaseDatabase.getInstance().getReference("User");
        Dexter.withContext(getApplicationContext())
                .withPermission(Manifest.permission.CAMERA)
                .withListener(new PermissionListener() {
                    @Override
                    public void onPermissionGranted(PermissionGrantedResponse permissionGrantedResponse) {
                        scannerView.startCamera();
                    }

                    @Override
                    public void onPermissionDenied(PermissionDeniedResponse permissionDeniedResponse) {

                    }

                    @Override
                    public void onPermissionRationaleShouldBeShown(PermissionRequest permissionRequest, PermissionToken permissionToken) {
                        permissionToken.continuePermissionRequest();
                    }
                }).check();
    }

    @Override
    public void handleResult(Result result) {
        String data = result.getText().toString();
        Date dateAndTime = (Date) Calendar.getInstance().getTime();
        SimpleDateFormat dateFormat = new SimpleDateFormat("MM/dd/yyyy", Locale.getDefault());
        SimpleDateFormat timeFormat = new SimpleDateFormat("hh:mm:ss", Locale.getDefault());
        String date = dateFormat.format(dateAndTime);
        String time = timeFormat.format(dateAndTime);
        String deviceId = Settings.Secure.getString(this.getContentResolver(), Settings.Secure.ANDROID_ID);
        getLocation();
        saveUser();
        String locationString = scanner.address.getText().toString();
        String name = scanner.name.getText().toString();
        String studNum = scanner.studNum.getText().toString();
        StoreInfo storeInfo = new StoreInfo(data, date, time, deviceId, locationString, name, studNum);

        dbref.push().setValue(storeInfo).addOnCompleteListener(new OnCompleteListener<Void>() {
            @Override
            public void onComplete(@NonNull Task<Void> task) {
                scanner.qrtext.setText("Course: " + data);
                scanner.date.setText("Date: " + date);
                scanner.arrival.setText("Arrival time: " + time);
                scanner.id.setText("Device Id: " + deviceId.toString());
                scanner.address.setText("Location: " + locationString);
                scanner.name.setText("Name: " + name);
                scanner.studNum.setText("Student Number: " + studNum);


                onBackPressed();
            }
        });
    }

    private void saveUser() {

        DatabaseReference ref = FirebaseDatabase.getInstance().getReference("User");
        FirebaseAuth auth     = FirebaseAuth.getInstance();
        FirebaseUser user     = auth.getCurrentUser();

        ref.addListenerForSingleValueEvent(new ValueEventListener() {
            @Override
            public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
                String nameString = dataSnapshot.child("userName").getValue(String.class);
                String studNumString = dataSnapshot.child("userStudNo").getValue(String.class);

                name.setText("" + nameString);
                studNum.setText("" + studNumString);
            }

            @Override
            public void onCancelled(@NonNull DatabaseError databaseError) {
            }
        });}

    private void getLocation() {

        if (ContextCompat.checkSelfPermission(this, Manifest.permission.ACCESS_FINE_LOCATION) == PackageManager.PERMISSION_GRANTED) {
            fusedLocationProviderClient.getLastLocation().addOnSuccessListener(new OnSuccessListener<Location>() {
                @Override
                public void onSuccess(Location location) {

                    if (location != null) {
                        try {
                            Geocoder geocoder = new Geocoder(qrscanner.this, Locale.getDefault());

                            List<Address> addresses = geocoder.getFromLocation(location.getLatitude(), location.getLongitude(), 1);
                            scanner.address.setText("Location: " + addresses.get(0).getAddressLine(0)
                            );
                        } catch (IOException e) {

                            e.printStackTrace();
                        }
                    }
                }
            });
        } else {
            askPermission();
        }
    }

    private void askPermission() {
        ActivityCompat.requestPermissions(qrscanner.this, new String[]{Manifest.permission.ACCESS_FINE_LOCATION}, REQUEST_CODE);
    }

    @Override
    public void onRequestPermissionsResult(int requestCode, @NonNull @org.jetbrains.annotations.NotNull String[] permissions, @NonNull @org.jetbrains.annotations.NotNull int[] grantResults) {

        if (requestCode == REQUEST_CODE) {
            if (grantResults.length > 0 && grantResults[0] == PackageManager.PERMISSION_GRANTED) {
                getLocation();
            } else {
                Toast.makeText(qrscanner.this, "Please provide the required permission", Toast.LENGTH_SHORT).show();
            }
        }

        super.onRequestPermissionsResult(requestCode, permissions, grantResults);
    }

    @Override
    protected void onPause() {
        super.onPause();
        scannerView.stopCamera();
    }

    @Override
    protected void onResume() {
        super.onResume();
        scannerView.setResultHandler(this);
        scannerView.startCamera();
    }
}

qrscanner.java will store the info of user in StoreInfo database

Solution

  • You're loading the User node, and then read the userName property from under that. But there is no userName property under User, as there's an extra layer in your JSON (201-0001 in the screenshot).

    You have to account for that extra layer, for example by looping over the children of dataSnapshot:

    DatabaseReference ref = FirebaseDatabase.getInstance().getReference("User");
FirebaseAuth auth = FirebaseAuth.getInstance();
FirebaseUser user = auth.getCurrentUser();

ref.addListenerForSingleValueEvent(new ValueEventListener() {
    @Override
    public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
        for (DataSnapshot userSnapshot: dataSnapshot.getChildren()) { // 👈 loop over child nodes
            String nameString = userSnapshot.child("userName").getValue(String.class);
            String studNumString = userSnapshot.child("userStudNo").getValue(String.class);

            name.setText("" + nameString);
            studNum.setText("" + studNumString);
        }
    }

    @Override
    public void onCancelled(@NonNull DatabaseError databaseError) {
        throw databaseError.toException(); // 👈 never ignore errors
    }
});