Null pointer exception error sending a characteristic BLE android

Question

I'm a new android developer and I'm trying to send a data using BLE 4.3, based on Gatt android sample project.

I use characteristics to put the data that i want to transmit.

When I try to transmit, I use the third service in the list of DeviceControlActivity of the project, appears a text dialog to introduce text. When I press OK, the idea is that start the transmission, but I obtain a NullPointerException error.

I don't know why appears this error and how can I solve this.

This is my full code, if this is useful

package com.example.blem;

public class DeviceControlActivity extends Activity {

public static final String EXTRAS_DEVICE_NAME = "DEVICE_NAME";
public static final String EXTRAS_DEVICE_ADDRESS = "DEVICE_ADDRESS";

private TextView mConnectionState;
private TextView mDataField;
private TextView mRssiField;
private String mDeviceName;
private String mDeviceAddress;
private ExpandableListView mGattServicesList;
private BluetoothLeService mBluetoothLeService;
private ArrayList<ArrayList<BluetoothGattCharacteristic>> mGattCharacteristics =
        new ArrayList<ArrayList<BluetoothGattCharacteristic>>();
private boolean mConnected = false;
private BluetoothGattCharacteristic mNotifyCharacteristic;
private BluetoothGattCharacteristic mWriteCharacteristic;
Button Escritor;
byte hello []={0};

private final String LIST_NAME = "NAME";
private final String LIST_UUID = "UUID";

BluetoothGattCharacteristic characteristic;

public BluetoothGatt mBluetoothGatt;
// Code to manage Service lifecycle.
private final ServiceConnection mServiceConnection = new ServiceConnection() {

    @Override
    public void onServiceConnected(ComponentName componentName, IBinder service) {
        mBluetoothLeService = ((BluetoothLeService.LocalBinder) service).getService();
        if (!mBluetoothLeService.initialize()) {
            Log.e("Unable to initialize Bluetooth");
            finish();
        }
        // Automatically connects to the device upon successful start-up initialization.
        mBluetoothLeService.connect(mDeviceAddress);
        mBluetoothLeService.setBLEServiceCb(mDCServiceCb);
    }

    @Override
    public void onServiceDisconnected(ComponentName componentName) {
        mBluetoothLeService = null;
    }
};

// If a given GATT characteristic is selected, check for supported features.  This sample
// demonstrates 'Read' and 'Notify' features.  See
// http://d.android.com/reference/android/bluetooth/BluetoothGatt.html for the complete
// list of supported characteristic features.
private final ExpandableListView.OnChildClickListener servicesListClickListner =
        new ExpandableListView.OnChildClickListener() {
            @TargetApi(Build.VERSION_CODES.JELLY_BEAN_MR2)
            @Override
            public boolean onChildClick(ExpandableListView parent, View v, int groupPosition,
                                        int childPosition, long id) {
                if (mGattCharacteristics != null) {
                    final BluetoothGattCharacteristic characteristic =
                            mGattCharacteristics.get(groupPosition).get(childPosition);
                    final int charaProp = characteristic.getProperties();
                    if ((charaProp & BluetoothGattCharacteristic.PROPERTY_READ) > 0) {
                        // If there is an active notification on a characteristic, clear
                        // it first so it doesn't update the data field on the user interface.
                        Log.d("BluetoothGattCharacteristic has PROPERTY_READ, so send read request");

                        if (mNotifyCharacteristic != null) {
                            mBluetoothLeService.setCharacteristicNotification(
                                    mNotifyCharacteristic, false);
                            mNotifyCharacteristic = null;
                        }
                        mBluetoothLeService.readCharacteristic(characteristic);
                    }

                    if ((charaProp & BluetoothGattCharacteristic.PROPERTY_NOTIFY) > 0) {
                        Log.d("BluetoothGattCharacteristic has PROPERTY_NOTIFY, so send notify request");

                        mNotifyCharacteristic = characteristic;
                        mBluetoothLeService.setCharacteristicNotification(
                                characteristic, true);
                    }

                    if (((charaProp & BluetoothGattCharacteristic.PROPERTY_WRITE) |
                            (charaProp & BluetoothGattCharacteristic.PROPERTY_WRITE_NO_RESPONSE)) > 0) {
                        Log.d("BluetoothGattCharacteristic has PROPERY_WRITE | PROPERTY_WRITE_NO_RESPONSE");

                        mWriteCharacteristic = characteristic;
                        // popup an dialog to write something.
                        showCharactWriteDialog();
                    }
                    return true;
                }
                return false;
            }
};

private void showCharactWriteDialog() {
    DialogFragment newFrame = new BleCharacterDialogFragment();
    newFrame.show(getFragmentManager(), "blewrite");
}

private void clearUI() {
    mGattServicesList.setAdapter((SimpleExpandableListAdapter) null);
    mDataField.setText(R.string.no_data);
}

@TargetApi(Build.VERSION_CODES.HONEYCOMB)
@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.gatt_services_characteristics);

    final Intent intent = getIntent();
    mDeviceName = intent.getStringExtra(EXTRAS_DEVICE_NAME);
    mDeviceAddress = intent.getStringExtra(EXTRAS_DEVICE_ADDRESS);

    // Sets up UI references.
    ((TextView) findViewById(R.id.device_address)).setText(mDeviceAddress);
    mGattServicesList = (ExpandableListView) findViewById(R.id.gatt_services_list);
    mGattServicesList.setOnChildClickListener(servicesListClickListner);
    mConnectionState = (TextView) findViewById(R.id.connection_state);
    mDataField = (TextView) findViewById(R.id.data_value);
    mRssiField = (TextView) findViewById(R.id.signal_rssi);

    //Escritor = (Button) findViewById(R.id.escrito);

    /*Escritor.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {

            characteristic.setValue(new byte[] {(byte) 0xFF});
            writeCharacteristicValue(characteristic);

            Toast.makeText(getApplicationContext(), "Se envío el dato",
                    Toast.LENGTH_SHORT).show();

            return;
        }
    });*/

    getActionBar().setTitle(mDeviceName);
    getActionBar().setDisplayHomeAsUpEnabled(true);
    Intent gattServiceIntent = new Intent(this, BluetoothLeService.class);
    bindService(gattServiceIntent, mServiceConnection, BIND_AUTO_CREATE);
}

@Override
protected void onResume() {
    super.onResume();
    //registerReceiver(mGattUpdateReceiver, makeGattUpdateIntentFilter());
    if (mBluetoothLeService != null) {
        final boolean result = mBluetoothLeService.connect(mDeviceAddress);
        Log.d("Connect request result=" + result);
    }
}

@Override
protected void onPause() {
    super.onPause();
    //unregisterReceiver(mGattUpdateReceiver);
}

@Override
protected void onDestroy() {
    super.onDestroy();
    unbindService(mServiceConnection);
    mBluetoothLeService = null;
}

@Override
public boolean onCreateOptionsMenu(Menu menu) {
    getMenuInflater().inflate(R.menu.gatt_services, menu);
    if (mConnected) {
        menu.findItem(R.id.menu_connect).setVisible(false);
        menu.findItem(R.id.menu_disconnect).setVisible(true);
    } else {
        menu.findItem(R.id.menu_connect).setVisible(true);
        menu.findItem(R.id.menu_disconnect).setVisible(false);
    }
    return true;
}

@TargetApi(Build.VERSION_CODES.ECLAIR)
@Override
public boolean onOptionsItemSelected(MenuItem item) {
    switch(item.getItemId()) {
        case R.id.menu_connect:
            mBluetoothLeService.connect(mDeviceAddress);
            return true;
        case R.id.menu_disconnect:
            mBluetoothLeService.disconnect();
            return true;
        case android.R.id.home:
            onBackPressed();
            return true;
    }
    return super.onOptionsItemSelected(item);
}

private void updateConnectionState(final int resourceId) {
    runOnUiThread(new Runnable() {
        @Override
        public void run() {
            mConnectionState.setText(resourceId);
        }
    });
}

private void displayData(String data) {
    if (data != null) {
        mDataField.setText(data);
    }
}

private void displayRssi(String rssi) {
    if (rssi != null) {
        //Log.d("-- dispaly Rssi: " + rssi);
        mRssiField.setText(rssi);
    }
}
// Demonstrates how to iterate through the supported GATT Services/Characteristics.
// In this sample, we populate the data structure that is bound to the ExpandableListView
// on the UI.
@TargetApi(Build.VERSION_CODES.JELLY_BEAN_MR2)
private void displayGattServices(List<BluetoothGattService> gattServices) {
    Log.d("displayGATTServices");

    if (gattServices == null) return;
    String uuid = null;
    String unknownServiceString = getResources().getString(R.string.unknown_service);
    String unknownCharaString = getResources().getString(R.string.unknown_characteristic);
    ArrayList<HashMap<String, String>> gattServiceData = new ArrayList<HashMap<String, String>>();
    ArrayList<ArrayList<HashMap<String, String>>> gattCharacteristicData
            = new ArrayList<ArrayList<HashMap<String, String>>>();
    mGattCharacteristics = new ArrayList<ArrayList<BluetoothGattCharacteristic>>();

    // Loops through available GATT Services.
    for (BluetoothGattService gattService : gattServices) {
        HashMap<String, String> currentServiceData = new HashMap<String, String>();
        uuid = gattService.getUuid().toString();
        currentServiceData.put(
                LIST_NAME, SampleGattAttributes.lookup(uuid, unknownServiceString));
        currentServiceData.put(LIST_UUID, uuid);
        gattServiceData.add(currentServiceData);

        ArrayList<HashMap<String, String>> gattCharacteristicGroupData =
                new ArrayList<HashMap<String, String>>();
        List<BluetoothGattCharacteristic> gattCharacteristics =
                gattService.getCharacteristics();
        ArrayList<BluetoothGattCharacteristic> charas =
                new ArrayList<BluetoothGattCharacteristic>();

        // Loops through available Characteristics.
        for (BluetoothGattCharacteristic gattCharacteristic : gattCharacteristics) {
            charas.add(gattCharacteristic);
            HashMap<String, String> currentCharaData = new HashMap<String, String>();
            uuid = gattCharacteristic.getUuid().toString();
            currentCharaData.put(
                    LIST_NAME, SampleGattAttributes.lookup(uuid, unknownCharaString));
            currentCharaData.put(LIST_UUID, uuid);
            gattCharacteristicGroupData.add(currentCharaData);
        }
        mGattCharacteristics.add(charas);
        gattCharacteristicData.add(gattCharacteristicGroupData);
    }

    SimpleExpandableListAdapter gattServiceAdapter = new SimpleExpandableListAdapter(
            this,
            gattServiceData,
            android.R.layout.simple_expandable_list_item_2,
            new String[] {LIST_NAME, LIST_UUID},
            new int[] { android.R.id.text1, android.R.id.text2 },
            gattCharacteristicData,
            android.R.layout.simple_expandable_list_item_2,
            new String[] {LIST_NAME, LIST_UUID},
            new int[] { android.R.id.text1, android.R.id.text2 }
    );
    mGattServicesList.setAdapter(gattServiceAdapter);
}

private DCServiceCb mDCServiceCb = new DCServiceCb();

public class DCServiceCb implements BluetoothLeService.BLEServiceCallback {

    @Override
    public void displayRssi(final int rssi) {
        runOnUiThread(new Runnable() {
              @Override
              public void run() {
                  DeviceControlActivity.this.displayRssi(String.valueOf(rssi));
                }
            }
        );
    }

    @Override
    public void displayData(final String data) {
        runOnUiThread(new Runnable() {
            @Override
            public void run() {
                DeviceControlActivity.this.displayData(data);
            }
        });
    }

    @Override
    public void notifyConnectedGATT() {
        runOnUiThread(new Runnable() {
            @Override
            public void run() {
                mConnected = true;
                updateConnectionState(R.string.connected);
                invalidateOptionsMenu();
            }
        });
    }

    @Override
    public void notifyDisconnectedGATT() {
        runOnUiThread(new Runnable() {
            @Override
            public void run() {
                mConnected = false;
                updateConnectionState(R.string.disconnected);
                invalidateOptionsMenu();
                clearUI();
            }
        });
    }

    @Override
    public void displayGATTServices() {
        Log.d("displayGATTServices.");
        runOnUiThread(new Runnable() {
            @Override
            public void run() {
                if (mBluetoothLeService != null) {
                    DeviceControlActivity.this.displayGattServices(
                            mBluetoothLeService.getSupportedGattServices());
                }
            }
        });
    }
}

@SuppressLint("ValidFragment")
public class BleCharacterDialogFragment extends DialogFragment {

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {
        View v = inflater.inflate(R.layout.write_charact_dialog, container, false);
        final EditText ed = (EditText) v.findViewById(R.id.charact_value);
        Button ok = (Button) v.findViewById(R.id.dialog_confirm);
        Button cancel = (Button) v.findViewById(R.id.dialog_cancel);

        ok.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                characteristic.setValue(hello);
                //characteristic.setValue("FF");
                //characteristic.setValue(new byte[] {(byte) 0xFF});
                writeCharacteristicValue(characteristic);

                Toast.makeText(getApplicationContext(), "Se envío el dato",
                        Toast.LENGTH_SHORT).show();
                dismiss();
                return;
            }
        });

        cancel.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                dismiss();
            }
        });

        return v;
    }
}

public void writeCharacteristicValue(BluetoothGattCharacteristic characteristica)
{
    byte[] value= {(byte) 0xFF};
    characteristica.setValue(bytesToHex(value));
    boolean status = mBluetoothGatt.writeCharacteristic(characteristica);
}

final protected static char[] hexArray = "0123456789ABCDEF".toCharArray();

public String bytesToHex(byte[] bytes) 
{
    char[] hexChars = new char[bytes.length * 2];
    int v;
    for ( int j = 0; j < bytes.length; j++ ) 
    {
        v = bytes[j] & 0xFF;
        hexChars[j * 2] = hexArray[v >>> 4];
        hexChars[j * 2 + 1] = hexArray[v & 0x0F];
    }
    return new String(hexChars);
}

}

Can someone tell what I'm doing wrong?

Thanks for advance

Sochi

look at the stacktrace and see the caused by part. – Temblor

Answer 1

Without the stack trace this is impossible to truly debug, but from the looks of it you aren't using the onServicesDiscovered() and onCharacteristicRead() callbacks to wait for all the service and respective characteristics to be read so you have no idea when these events are occurring and thus are able to continue

Notornis