onCharacteristicChanged is not called in Android BLE GATT servcies

Question

I am trying to receive the data from BLE device in my app. i could able to connect the BLE device successfully with my app and i am able to find the services provided by the BLE devices.

I can able to write data in characteristics and able to enable notification for particular service successfully and its returning TRUE . Issue is after gatt.writeCharacteristic(characteristic) successfully it should call onCharacteristicChanged override method. But its not calling that method. from that method only i can able to receive the data from BLE device.

I Followed below url

Android BLE

Note: By using service , i am invoking establishing GATT connection.

 private class BleGattCallback extends BluetoothGattCallback {
        @Override
        public void onConnectionStateChange(BluetoothGatt gatt, int status, int newState) {

            switch (newState) {
                case BluetoothProfile.STATE_CONNECTED:

                     gatt.discoverServices();

                    break;

                case BluetoothProfile.STATE_DISCONNECTED:
                    Log.d(TAG, "BluetoothProfile.STATE_DISCONNECTED");
                    gatt.close();
                    break;

                default:
                    break;
            }
        }


        @Override
        public void onServicesDiscovered(BluetoothGatt gatt, int status) {
            Log.d(TAG, "onServicesDiscovered");

            if (status == BluetoothGatt.GATT_SUCCESS) {
                BluetoothGattService service = gatt.getService(SERVICE_UUID);
                if (service != null) {

                    BluetoothGattCharacteristic characteristic = service.getCharacteristic(READING_UUID);
                    if (characteristic != null) {
                        Log.d(TAG, " Subscribe Characteristic Notification UUID :  "+characteristic.getUuid());

                        gatt.setCharacteristicNotification(characteristic, true);

                        BluetoothGattDescriptor descriptor = characteristic.getDescriptor(CHARACTERISTIC_UUID);
                        descriptor.setValue(BluetoothGattDescriptor.ENABLE_NOTIFICATION_VALUE);

                        boolean success = gatt.writeDescriptor(descriptor);


                        Log.d(TAG, "writeDescriptor Status : " + success);
                    }
                }
            }
        }


        @Override
        public void onCharacteristicChanged(BluetoothGatt gatt, BluetoothGattCharacteristic characteristic) {
            super.onCharacteristicChanged(gatt, characteristic);

            Toast.makeText(mContext,"onCharacteristicChanged",Toast.LENGTH_LONG).show();
            // read Value
        }



        @Override
        public void onDescriptorWrite(BluetoothGatt gatt, BluetoothGattDescriptor descriptor, int status) {
            super.onDescriptorWrite(gatt, descriptor, status);


            if (status == BluetoothGatt.GATT_SUCCESS) {

                BluetoothGattService service = gatt.getService(SERVICE_UUID);
                if (service != null) {
                    BluetoothGattCharacteristic characteristic = service.getCharacteristic(INDEX_UUID);
                    Log.d(TAG, "onDescriptorWrite  success UUID for "+characteristic.getUuid());
                    if (characteristic != null) {
                        characteristic.setValue(new byte[] {0x03, 0x00});
                        gatt.writeCharacteristic(characteristic);
                    }
                }
            }
        }


    }

Answer 1

No. onCharacteristicChanged is not called after you write a value to a characteristic. onCharacteristicWrite is called.

onCharacteristicChanged is called when a notification or indication has been received.