Unable to read/write some characateristics from BLE device using the BluetoothLeGatt app

Question

I have been working with the BluetoothLeGatt application. I am trying to read characteristics from a BLE device- TI CC2541 Keyfob. I am able to read and write into some characteristics, but failing to do so to some other characteristics. All these services and characteristics are listed in the expandableListView. But on selecting some of them, their values and not getting displayed. Can anybody help me out with this problem.

Is there a way to read value using Characteristic Value Handle

"I am able to read and write into some characteristics, but failing to do so to some other characteristics." In what way do you mean with "fail"? Are there any errors? Note that you can only have one pending GATT command outstanding. You need to wait for the appropriate callback before you can issue the next one. — Emil
No errors. I think the mistake is that I am trying to read characteristics with notify permission. — sp9

Rajasekhar Rajasekhar · Accepted Answer · 2016-12-01T06:49:13

**For Write characterstics Steps :

1. First you have to do indicate
2. After executing indication onDecriptor write sucessfull is executed.Here you have to start write characterstics.**

// for indicate the follwing code is in BluetoothLEService

 public void indicateCharacteristic(UUID serviceUUID, UUID characteristicUuid, boolean isIndicate) {
        try {
            UUID serviceuid = serviceUUID;
            if (serviceuid != null && mBluetoothGatt != null) {
                BluetoothGattService service = mBluetoothGatt.getService(serviceuid);
                UUID characteristicuid = characteristicUuid;
                BluetoothGattCharacteristic characteristic = null;
                if (service != null) {
                    characteristic = service.getCharacteristic(characteristicuid);
                    //Enable local notifications
                    if (mBluetoothGatt != null) {
                        mBluetoothGatt.setCharacteristicNotification(characteristic, isIndicate);
                        ArrayList<BluetoothGattDescriptor> gattdescriptor = (ArrayList<BluetoothGattDescriptor>) characteristic
                                .getDescriptors();

                        for (int k = 0; k < gattdescriptor.size(); k++) {

                            BluetoothGattDescriptor descriptor = gattdescriptor.get(k);
                            if (descriptor.getUuid().toString().equalsIgnoreCase(GattAttributes.CLIENT_CHARACTERISTIC_CONFIG))
                                writeGattDescriptorForIndication(descriptor, isIndicate);
                        }

                    }
                }
            }
        } catch (Exception e) {
            Log.d("device", "not found");
        }
    }

    // Write gatt descriptor
    public void writeGattDescriptorForIndication(BluetoothGattDescriptor d, boolean isIndicate) {
        boolean test;
        if (isIndicate) {
            d.setValue(BluetoothGattDescriptor.ENABLE_NOTIFICATION_VALUE);
            d.setValue(BluetoothGattDescriptor.ENABLE_INDICATION_VALUE);
        } else {
            d.setValue(BluetoothGattDescriptor.DISABLE_NOTIFICATION_VALUE);
        }
        //  test = mBluetoothGatt.readDescriptor(d);  // return value = true
        // Log.d("test",""+test);
        test = mBluetoothGatt.writeDescriptor(d);
        Log.d("test", "" + test);
    }


@Override
    public void onCharacteristicWrite(BluetoothGatt gatt, BluetoothGattCharacteristic characteristic, int status) {
        if (characteristic.getUuid().toString().equals(GattAttributes.BATTERY_LEVEL_CHARACTERSTIC_UUID))
            broadcastUpdate(ACTION_DATA_AVAILABLE, characteristic);

    }

    @Override
    public void onDescriptorWrite(BluetoothGatt gatt, BluetoothGattDescriptor descriptor, int status) {
        if (status == BluetoothGatt.GATT_SUCCESS) {

                writeStartCommand();
                Log.d(TAG, "volume Descriptor writing successful");

        } else if (status == BluetoothGatt.GATT_INSUFFICIENT_AUTHENTICATION) {
            // this is where the tricky part comes
            if (gatt.getDevice().getBondState() == BluetoothDevice.BOND_NONE) {
                Log.e(TAG, "Bonding required!!!");
            } else {
                // this situation happens when you try to connect for the
                // second time to already bonded device
                // it should never happen, in my opinion
                Log.e(TAG, "The phone is trying to read from paired device without encryption. Android Bug?");
                // I don't know what to do here
                // This error was found on Nexus 7 with KRT16S build of
                // Andorid 4.4. It does not appear on Samsung S4 with
                // Andorid 4.3.
            }
        } else {
            Log.e(TAG, "Error writing descriptor, status: " + status);
        }

    }
};

public void writeStartCommand() {
    int val = 0x55;
    doWrite(UUID.fromString(GattAttributes.BATTERY_LEVEL_SERVICE_UUID), UUID.fromString(GattAttributes.VOLUME_START_SERVICE_UUID), val);
    waitSometime(100);
}

public synchronized void doWrite(UUID gatservice_uuid, UUID char_uuid, int value) {
    try {
        byte[] value1 = new byte[1];
        value1[0] = (byte) (Integer.valueOf(value) & 0xFF);
        BluetoothGattService mSVC = mBluetoothGatt.getService(gatservice_uuid);
        BluetoothGattCharacteristic mCH = mSVC.getCharacteristic(char_uuid);
        mCH.setValue(value1);
        Log.d("write val", "" + value1);
        // mCH.setValue(value, BluetoothGattCharacteristic.FORMAT_UINT8, 0);
        // mCH.setWriteType(BluetoothGattCharacteristic.PROPERTY_WRITE_NO_RESPONSE);
        if (mBluetoothGatt.writeCharacteristic(mCH)) {
            waitSometime(100);
            Log.d("sucess", "write characteristics successfully stored-" + char_uuid);
        } else {
            Log.d("fail", "write characteristics failed-" + char_uuid);
           /* if(char_uuid.toString().equalsIgnoreCase(GattAttributes.CALIBRATION_START_COMMAND_UUID)){
                Thread.sleep(100);
                isWriting
                writeStopCommand();
            }else {
                Toast.makeText(CalibrationLeService.this, "Write Characteristics failed"+char_uuid.toString(), Toast.LENGTH_SHORT).show();
            }*/
            //sendBroadcast(new Intent(BluetoothLeForegroundService.ACTION_FINISH));
        }
    } catch (Exception e) {
        Log.d("characteristic id is", "discoverd services not available");
    }
}

public synchronized void waitSometime(int seconds) {
    try {
        Thread.sleep(seconds);
    } catch (InterruptedException e) {
        e.printStackTrace();
    }
}

// And then finally in your activity just call

public static String BATTERY_LEVEL_SERVICE_UUID         = "5956efdd-7272-4bfe-937a-f17c70e86b55"; // Volume level service UUID
public static String BATTERY_LEVEL_CHARACTERSTIC_UUID   = "a5bd1e6a-db71-4da5-9b42-a59800e4538b";     
 mBluetoothLeForegroundService.indicateCharacteristic(UUID.fromString(GattAttributes.BATTERY_LEVEL_SERVICE_UUID), UUID.fromString(GattAttributes.BATTERY_LEVEL_CHARACTERSTIC_UUID), true);

Unable to read/write some characateristics from BLE device using the BluetoothLeGatt app

1 Answers