onScannerClosedWithResult(no.nordicsemi.android.beacon.Beacon)' on a null object reference

Question

I am trying to write a app which scans for beacons, when I login to the app, it starts scanning but after some seconds it just crashes. if I turn off my bluetooth it works fine. this is the error I get:

  Process: com.noxel.apppaneladmintry2, PID: 11192
java.lang.NullPointerException: Attempt to invoke virtual method 'void com.example.niloofar.showroom.BeaconsFragment.onScannerClosed()' on a null object reference
        at com.example.niloofar.showroom.BeaconScannerFragment.onCancel(BeaconScannerFragment.java:56)
        at android.app.Dialog$ListenersHandler.handleMessage(Dialog.java:1260)
        at android.os.Handler.dispatchMessage(Handler.java:102)
        at android.os.Looper.loop(Looper.java:135)
        at android.app.ActivityThread.main(ActivityThread.java:5257)
        at java.lang.reflect.Method.invoke(Native Method)
        at java.lang.reflect.Method.invoke(Method.java:372)
        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:921)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:716)

and this is my code,

    package com.example.niloofar.showroom;

import android.bluetooth.BluetoothAdapter;
import android.bluetooth.BluetoothManager;
import android.content.ActivityNotFoundException;
import android.content.BroadcastReceiver;
import android.content.Context;
import android.content.DialogInterface;
import android.content.Intent;
import android.content.pm.PackageManager;
import android.database.Cursor;
import android.net.Uri;
import android.os.Bundle;
import android.os.Handler;
import android.support.design.widget.FloatingActionButton;
import android.support.design.widget.Snackbar;
import android.support.v4.app.Fragment;
import android.support.v4.app.FragmentTransaction;
import android.support.v7.app.AlertDialog;
import android.util.Log;
import android.view.View;
import android.support.design.widget.NavigationView;
import android.support.v4.view.GravityCompat;
import android.support.v4.widget.DrawerLayout;
import android.support.v7.app.ActionBarDrawerToggle;
import android.support.v7.app.AppCompatActivity;
import android.support.v7.widget.Toolbar;
import android.view.Menu;
import android.view.MenuItem;
import android.widget.Toast;

import java.util.UUID;

import no.nordicsemi.android.beacon.Beacon;
import no.nordicsemi.android.beacon.BeaconRegion;
import no.nordicsemi.android.beacon.BeaconServiceConnection;
import no.nordicsemi.android.beacon.Proximity;
import no.nordicsemi.android.beacon.ServiceProxy;

public class drawermenu extends AppCompatActivity implements NavigationView.OnNavigationItemSelectedListener, BeaconServiceConnection.BeaconsListener, BeaconServiceConnection.RegionListener {
public ProfileFragment profileFragment;
    private static final String SCANNER_FRAGMENT = "scannerFragment";
    public static final String NRF_BEACON_SERVICE_URL = "market://details?id=no.nordicsemi.android.beacon.service";
    public static final String OPENED_FROM_LAUNCHER = "no.nordicsemi.android.nrfbeacon.extra.opened_from_launcher";
    public static final String EXTRA_OPEN_DFU = "no.nordicsemi.android.nrfbeacon.extra.open_dfu";
    public static final int BEACON_COMPANY_ID = 0x0059;
    private static final int REQUEST_ENABLE_BT = 1;
    private boolean mServiceConnected;
    private boolean mFragmentResumed;
    private DatabaseHelper mDatabaseHelper;
    private BeaconAdapter mAdapter;
    private BeaconScannerFragment mScannerFragment;
    int minor;
    public Fragment fragment=null;

    public FragmentA fragmentA;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        try {
            super.onCreate(savedInstanceState);
            setContentView(R.layout.activity_main);
            Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);

            BluetoothAdapter mBluetoothAdapter = BluetoothAdapter.getDefaultAdapter();
            if (mBluetoothAdapter == null) {
// Device does not support Bluetooth
                Toast.makeText(this, "Device dows not support Bluetooth", Toast.LENGTH_LONG);
            } else {
                if (!mBluetoothAdapter.isEnabled()) {
                    Intent enableBtIntent = new Intent(BluetoothAdapter.ACTION_REQUEST_ENABLE);
                    startActivityForResult(enableBtIntent, REQUEST_ENABLE_BT);
                }

            }

            mDatabaseHelper = new DatabaseHelper(this);

            getSupportActionBar().setElevation(0);

            DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
            ActionBarDrawerToggle toggle = new ActionBarDrawerToggle(
                    this, drawer, toolbar, R.string.navigation_drawer_open, R.string.navigation_drawer_close);
            drawer.setDrawerListener(toggle);
            toggle.syncState();

            NavigationView navigationView = (NavigationView) findViewById(R.id.nav_view);
            navigationView.setNavigationItemSelectedListener(this);
        }catch (Exception ex) {
            Log.d("ERROR", ex.getMessage());
        }
    }

    @Override
    public void onStart() {
        super.onStart();
        //   final Cursor cursor = mDatabaseHelper.getAllRegions();
        bindService();
    }

    @Override
    public void onResume() {
        super.onResume();
        //  startScanning();
        if (mFragmentResumed)
            return;

        mFragmentResumed = true;
        //  bindService();
        onAddOrEditRegion();
    }

    @Override
    public void onPause() {
        super.onPause();
        //  stopScanning();

        if (!mFragmentResumed)
            return;

        mFragmentResumed = false;
        unbindService();
    }

    private BeaconServiceConnection mServiceConnection = new BeaconServiceConnection() {
        @Override
        public void onServiceConnected() {
            try {
                mServiceConnected = true;

                final BeaconScannerFragment scannerFragment = mScannerFragment;
                if (scannerFragment != null) {
                    startRangingBeaconsInRegion(BEACON_COMPANY_ID, BeaconRegion.ANY_UUID, scannerFragment);
                } else {
                    //   final FragmentManager fm = getChildFragmentManager();
                    //  if (fm.getBackStackEntryCount() == 0) {
                    // Start scan only if there is no any other fragment (Mona Lisa) open
                    startScanning();
                    //   }
                }

            } catch (Exception ex) {
                Log.d("ERROR", ex.getMessage());
            }
        }

        @Override
        public void onServiceDisconnected() {
            try {
                mServiceConnected = false;
            } catch (Exception ex) {
                Log.e("ERROR", ex.getMessage());
            }
        }
    };

    public void onAddOrEditRegion() {
//        if (!ensurePermission())
//            return;
        try {
            stopScanning();
            //    mScannerFragment=null;
            final BeaconScannerFragment fragment = mScannerFragment = new BeaconScannerFragment();
            fragment.show(getSupportFragmentManager(), SCANNER_FRAGMENT);
            //    fragment.isHidden();
            mServiceConnection.startRangingBeaconsInRegion(BEACON_COMPANY_ID, BeaconRegion.ANY_UUID, fragment);
        }
        catch (Exception ex) {
            Log.e("ERROR", ex.getMessage());
        }
    }

    public void startScanning() {
        try {
            if (mServiceConnected) {
                startScanning(mServiceConnection);
            }
        } catch (Exception ex) {
            Log.e("ERROR", ex.getMessage());
        }
    }

    public void stopScanning() {
        try {
            if (mServiceConnected) {
                stopScanning(mServiceConnection);
            }
        } catch (Exception ex) {
            Log.e("ERROR", ex.getMessage());
        }
    }

    private void bindService() {
//        if (!ensurePermission())
//            return;
        try {
            final boolean success = ServiceProxy.bindService(this, mServiceConnection);
            if (!success) {
                new AlertDialog.Builder(this).setTitle(R.string.service_required_title).setMessage(R.string.service_required_message)
                        .setPositiveButton(R.string.service_required_store, new DialogInterface.OnClickListener() {
                            @Override
                            public void onClick(final DialogInterface dialog, final int which) {
                                final Intent playIntent = new Intent(Intent.ACTION_VIEW, Uri.parse(MainActivity.NRF_BEACON_SERVICE_URL));
                                startActivity(playIntent);
                            }
                        }).setOnCancelListener(new DialogInterface.OnCancelListener() {
                    @Override
                    public void onCancel(final DialogInterface dialog) {
                        dialog.dismiss();
                        finish();
                    }
                }).show();
            }
        } catch (Exception ex) {
            Log.e("ERROR", ex.getMessage());
        }
    }

    private void unbindService() {
        try {
            if (mServiceConnected) {
                // Unbinding service will stop all active scanning listeners
                ServiceProxy.unbindService(this, mServiceConnection);
                mDatabaseHelper.resetSignalStrength();
            }
        } catch (Exception ex) {
            Log.e("ERROR", ex.getMessage());
        }
    }

    public void startScanning(final BeaconServiceConnection serviceConnection) {
        try {
            final Cursor cursor = mDatabaseHelper.getAllRegions();
            while (cursor.moveToNext()) {
                final UUID uuid = UUID.fromString(cursor.getString(2 /* UUID */));
                final int major = cursor.getInt(3 /* MAJOR */);
                final int minor = cursor.getInt(4 /* MINOR */);
                final int event = cursor.getInt(6 /* EVENT */);

                // We must start ranging for all beacons
                serviceConnection.startRangingBeaconsInRegion(BEACON_COMPANY_ID, uuid, major, minor, this);
                // And additionally start monitoring only for those with these two events set
                if (event == BeaconContract.EVENT_IN_RANGE || event == BeaconContract.EVENT_OUT_OF_RANGE)
                    serviceConnection.startMonitoringForRegion(BEACON_COMPANY_ID, uuid, major, minor, this);
            }
        } catch (Exception ex) {

            Log.e("ERROR", ex.getMessage());
        }
    }

    public void stopScanning(final BeaconServiceConnection serviceConnection) {
        try {

            if (serviceConnection != null) {
                serviceConnection.stopMonitoringForRegion(this);
                serviceConnection.stopRangingBeaconsInRegion(this);
            }
        } catch (Exception ex) {

            Log.e("ERROR", ex.getMessage());
        }
    }

    @Override
    public void onBeaconsInRegion(final Beacon[] beacons, final BeaconRegion region) {
        try {
            if (beacons.length > 0) {
                final Cursor cursor = mDatabaseHelper.findRegion(region);
                try {
                    if (cursor.moveToNext()) {
                        // Check and fire events
                        final int event = cursor.getInt(6 /* EVENT */);
                        for (final Beacon beacon : beacons) {
                            if (event == BeaconContract.EVENT_ON_TOUCH && Proximity.IMMEDIATE.equals(beacon.getProximity()) && Proximity.NEAR.equals(beacon.getPreviousProximity())) {
                                fireEvent(cursor);
                                break;
                            }
                            if (event == BeaconContract.EVENT_GET_NEAR && Proximity.NEAR.equals(beacon.getProximity()) && Proximity.FAR.equals(beacon.getPreviousProximity())) {
                                fireEvent(cursor);
                                break;
                            }
                        }

                        // Update signal strength in the database
                        float accuracy = 5;
                        for (final Beacon beacon : beacons)
                            if (Proximity.UNKNOWN != beacon.getProximity() && beacon.getAccuracy() < accuracy)
                                accuracy = beacon.getAccuracy();
                        accuracy = -20 * accuracy + 100;
                        mDatabaseHelper.updateRegionSignalStrength(cursor.getLong(0 /* _ID */), (int) accuracy);
                    }
                } finally {
                    cursor.close();
                }
                mAdapter.swapCursor(mDatabaseHelper.getAllRegions());
            }
        } catch (Exception ex) {

            Log.e("ERROR", ex.getMessage());
        }
    }

    @Override
    public void onEnterRegion(final BeaconRegion region) {
        try {
            final Cursor cursor = mDatabaseHelper.findRegion(region);
            try {
                if (cursor.moveToNext()) {
                    final int event = cursor.getInt(6 /* EVENT */);
                    if (event == BeaconContract.EVENT_IN_RANGE) {
                        fireEvent(cursor);
                    }
                }
            } finally {
                cursor.close();
            }
        } catch (Exception ex) {

            Log.e("ERROR", ex.getMessage());
        }
    }

    @Override
    public void onExitRegion(final BeaconRegion region) {
        try {
            final Cursor cursor = mDatabaseHelper.findRegion(region);
            try {
                if (cursor.moveToNext()) {
                    final int event = cursor.getInt(6 /* EVENT */);
                    if (event == BeaconContract.EVENT_OUT_OF_RANGE) {
                        fireEvent(cursor);
                    }
                }
            } finally {
                cursor.close();
            }
        } catch (Exception ex) {

            Log.e("ERROR", ex.getMessage());
        }
    }

    private void fireEvent(final Cursor cursor) {
        try {
            final boolean enabled = cursor.getInt(9 /* ENABLED */) == 1;
            if (!enabled)
                return;

            final int action = cursor.getInt(7 /* ACTION */);
            final String actionParam = cursor.getString(8 /* ACTION PARAM */);

            switch (action) {
                case BeaconContract.ACTION_MONA_LISA: {
                    stopScanning();
                    //    final DialogFragment dialog = new MonalisaFragment();
                    //   dialog.show(mParentFragment.getChildFragmentManager(), "JIRNG");
                    break;
                }
                case BeaconContract.ACTION_SILENT: {
                    stopScanning();
                    //    final DialogFragment dialog = new tarh();
                    //    dialog.show(mParentFragment.getChildFragmentManager(), "JIRING");
                    break;
                }
                case BeaconContract.ACTION_ALARM: {
                    stopScanning();
                    //  final DialogFragment dialog = new rest();
                    //  dialog.show(mParentFragment.getChildFragmentManager(), "Jiring");
                    break;
                }
                case BeaconContract.ACTION_URL: {
                    stopScanning();
                    try {
                        final Intent intent = new Intent(Intent.ACTION_VIEW, Uri.parse(actionParam));
                        startActivity(intent);
                    } catch (final ActivityNotFoundException e) {
                        Toast.makeText(this, R.string.no_application, Toast.LENGTH_SHORT).show();
                    }
                    break;
                }
                case BeaconContract.ACTION_APP: {
                    stopScanning();
                    try {
                        final Intent intent = new Intent(Intent.ACTION_MAIN);
                        intent.setPackage(actionParam);
                        startActivity(intent);
                    } catch (final ActivityNotFoundException e) {
                        Toast.makeText(this, R.string.no_given_application, Toast.LENGTH_SHORT).show();
                    }
                    break;
                }
                case BeaconContract.ACTION_TASKER:
                    //   switch (TaskerIntent.testStatus(getActivity())) {
                    //      case OK:
                    //         final TaskerIntent i = new TaskerIntent(actionParam);
                    final BroadcastReceiver br = new BroadcastReceiver() {
                        @Override
                        public void onReceive(final Context context, final Intent recIntent) {
                            //            if (recIntent.getBooleanExtra(TaskerIntent.EXTRA_SUCCESS_FLAG, false))
                            Toast.makeText(drawermenu.this, R.string.tasker_success, Toast.LENGTH_SHORT).show();
                            drawermenu.this.unregisterReceiver(this);
                        }
                    };
                    //     getActivity().registerReceiver(br, i.getCompletionFilter());
                    // Start the task
                    //     getActivity().sendBroadcast(i);
                    break;
                //   case NotEnabled:
                //     Toast.makeText(getActivity(), R.string.tasker_disabled, Toast.LENGTH_SHORT).show();
                //   break;
                //    case AccessBlocked:
                //    Toast.makeText(getActivity(), R.string.tasker_external_access_denided, Toast.LENGTH_SHORT).show();
                //    break;
                //    case NotInstalled:
                //    Toast.makeText(getActivity(), R.string.tasker_not_installed, Toast.LENGTH_SHORT).show();
                //    break;
                default:
                    Toast.makeText(this, R.string.tasker_error, Toast.LENGTH_SHORT).show();
                    break;
            }
            //  break;
        } catch (Exception ex) {

            Log.e("ERROR", ex.getMessage());
        }
    }

    public void onEditRegion(final long id) {
//        final Intent intent = new Intent(this, BeaconsDetailsActivity.class);
//        intent.setFlags(Intent.FLAG_ACTIVITY_NO_ANIMATION);
//        intent.putExtra(BeaconsDetailsActivity.ID, id);
//        startActivity(intent);
    }

    public void onScannerClosedWithResult(final Beacon beacon) {
        try {
            mServiceConnection.stopRangingBeaconsInRegion(mScannerFragment);
            mScannerFragment.dismiss();

            mScannerFragment = null;
            // final Cursor cursor = mDatabaseHelper.findRegionByBeacon(beacon);

            minor = beacon.getMinor();

            Intent intenta = new Intent(drawermenu.this, FragmentA.class);
            switch (minor) {

                case 99:
                    //  startActivity(intenta);

                    popUp();
                    break;
                case 246:
//                    startActivity(intenta);
//                    Toast.makeText(MainActivity.this, "246", Toast.LENGTH_LONG).show();

                    popUp();


                    break;
                case 63:
                    popUp();
                    break;
                case 104:
                    popUp();

                    break;


            }
        }
        catch (Exception ex)
        {
            Log.e("ERROR", ex.getMessage());
        }
    }


    private void popUp()
    {

        new Handler().post(new Runnable() {
            @Override
            public void run() {
                /* Create an Intent that will start the Menu-Activity. */
                Intent mainIntent = new Intent(drawermenu.this,FragmentA.class);
                //   mainIntent.addFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP | Intent.FLAG_ACTIVITY_NEW_TASK);
                mainIntent.setFlags(Intent.FLAG_ACTIVITY_REORDER_TO_FRONT);

                drawermenu.this.startActivity(mainIntent);
                //   Splash.this.finish();
            }
        });
    }

    public void onScannerClosed() {
        try {
            mServiceConnection.stopRangingBeaconsInRegion(mScannerFragment);
            mScannerFragment = null;

            startScanning();
        } catch (Exception ex) {
            Log.e("ERROR", ex.getMessage());
        }
    }

    public DatabaseHelper getDatabaseHelper() {
        return mDatabaseHelper;
    }




    private boolean ensureBleExists() {
        try {
            if (!getPackageManager().hasSystemFeature(PackageManager.FEATURE_BLUETOOTH_LE)) {
                Toast.makeText(this, R.string.no_ble, Toast.LENGTH_LONG).show();
                return false;
            }
            return true;
        } catch (Exception ex) {
            Log.e("ERROR", ex.getMessage());
            return false;
        }
    }

    private boolean isBleEnabled() {
        try {
            final BluetoothManager bm = (BluetoothManager) getSystemService(BLUETOOTH_SERVICE);
            final BluetoothAdapter ba = bm.getAdapter();
            return ba != null && ba.isEnabled();
        } catch (Exception ex) {
            Log.e("ERROR", ex.getMessage());
            return false;
        }
    }

    private void enableBle() {
        try {
            final Intent enableIntent = new Intent(BluetoothAdapter.ACTION_REQUEST_ENABLE);
            startActivityForResult(enableIntent, REQUEST_ENABLE_BT);
        } catch (Exception ex) {
            Log.e("ERROR", ex.getMessage());

        }
    }



    @Override
    public void onBackPressed() {
        DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
        if (drawer.isDrawerOpen(GravityCompat.START)) {
            drawer.closeDrawer(GravityCompat.START);
        } else {
            super.onBackPressed();
        }
    }




    @SuppressWarnings("StatementWithEmptyBody")
    @Override
    public boolean onNavigationItemSelected(MenuItem item) {
        // Handle navigation view item clicks here.
        int id = item.getItemId();
        FragmentTransaction fragmentTransaction = getSupportFragmentManager().beginTransaction();

        if (id == R.id.nav_home) {
            // Handle the camera action
            fragment = new ProfileFragment();
        } else if (id == R.id.nav_points) {
            fragment = new PointFragment();
        } else if (id == R.id.nav_coupons) {
            fragment = new CouponFragment();
        } else if (id == R.id.nav_about) {
            fragment = new AboutFragment();
        }
        fragmentTransaction.replace(R.id.appbar, fragment,fragment.getClass().getSimpleName());
        fragmentTransaction.commit();
        DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);

        drawer.closeDrawer(GravityCompat.START);
        return true;
    }
}

and this is the code which error is referring to:

    package com.example.niloofar.showroom;

import android.app.Dialog;
import android.content.DialogInterface;
import android.os.Bundle;
import android.support.annotation.NonNull;
import android.support.v4.app.DialogFragment;
import android.support.v7.app.AlertDialog;

import no.nordicsemi.android.beacon.Beacon;
import no.nordicsemi.android.beacon.BeaconRegion;
import no.nordicsemi.android.beacon.BeaconServiceConnection;
import no.nordicsemi.android.beacon.Proximity;

/**
 * Created by niloofar on 11/9/2016.
 */
public class BeaconScannerFragment extends DialogFragment implements BeaconServiceConnection.BeaconsListener {
//    public class BeaconScannerFragment extends DialogFragment implements BeaconServiceConnection.BeaconsListener {
    private boolean mCompleted;

    @Override
    public void onCreate(final Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        mCompleted = false;
    }

    @Override
    public void onBeaconsInRegion(final Beacon[] beacons, final BeaconRegion region) {
        if (!mCompleted) {
            for (final Beacon beacon : beacons)
                if (Proximity.IMMEDIATE == beacon.getProximity()) {
                    mCompleted = true;

                    final BeaconsFragment parentFragment = (BeaconsFragment) getParentFragment();
                    parentFragment.onScannerClosedWithResult(beacon);
                    dismiss();
                    break;
                }
        }
    }

    @NonNull
    @Override
    public Dialog onCreateDialog(final Bundle savedInstanceState) {
        return new AlertDialog.Builder(getContext())
                .setView(R.layout.fragment_scan).create();
    }

    @Override
    public void onCancel(final DialogInterface dialog) {
        super.onCancel(dialog);

        final BeaconsFragment targetFragment = (BeaconsFragment) getParentFragment();
        targetFragment.onScannerClosed();
    }}

does anyone know how my problem will be solved?

Answer 1

This is the place where your problem occurs:

                final BeaconsFragment parentFragment = (BeaconsFragment) getParentFragment();
                parentFragment.onScannerClosedWithResult(beacon);

You initialize parentFragment, but the NullPointerException is thrown when you try to call onScannerClosedWithResult. This means that parentFragment is null. To solve this, you have three options. The first option is to use try-catch where you handle the NullPointerException. The second option is to make sure that getParentFragment will never return null. The third option is to fail gracefully when null is returned:

                final BeaconsFragment parentFragment = (BeaconsFragment) getParentFragment();
                if (parentFragment == null) {
                    parentFragment.onScannerClosedWithResult(beacon);
                }