在Android 6.0且API Level低于24。部分手机会无法接收到onCharacteristicChanged()所返回的消息，使用以下方法能够完美解决问题。

  public boolean enableNotification(BluetoothGatt gatt, UUID serviceUUID, UUID characteristicUUID) {
//        BluetoothGattService service = gatt.getService(serviceUUID);
//        BluetoothGattCharacteristic characteristic = findNotifyCharacteristic(service, characteristicUUID);
//        if (characteristic != null) {
//        if(bluetoothGatt.setCharacteristicNotification(characteristic2, true)){
//            //获取到Notify当中的Descriptor通道 然后再进行注册
//            BluetoothGattDescriptor clientConfig = characteristic2 .getDescriptor(UUID.fromString(DESCRIPTOR_UUID));
//            clientConfig.setValue(BluetoothGattDescriptor.ENABLE_NOTIFICATION_VALUE);
//            bluetoothGatt.writeDescriptor(clientConfig);
//        }
        boolean success = false;
        BluetoothGattService service = gatt.getService(serviceUUID);
        if (service != null) {
            BluetoothGattCharacteristic characteristic = findNotifyCharacteristic(service, characteristicUUID);
            if (characteristic != null) {
                success = gatt.setCharacteristicNotification(characteristic, true);
                gatt.readCharacteristic(characteristic);
                if (success) {
                    for(BluetoothGattDescriptor dp: characteristic.getDescriptors()){
                        if (dp != null) {
                            if ((characteristic.getProperties() & BluetoothGattCharacteristic.PROPERTY_NOTIFY) != 0) {
                                dp.setValue(BluetoothGattDescriptor.ENABLE_NOTIFICATION_VALUE);
                            } else if ((characteristic.getProperties() & BluetoothGattCharacteristic.PROPERTY_INDICATE) != 0) {
                                dp.setValue(BluetoothGattDescriptor.ENABLE_INDICATION_VALUE);
                            }
                            int writeType = characteristic.getWriteType();
                            Log.e(TAG, "enableNotification: "+writeType );                            characteristic.setWriteType(BluetoothGattCharacteristic.WRITE_TYPE_DEFAULT);
                            bluetoothGatt.writeDescriptor(dp);
                            characteristic.setWriteType(writeType);
                        }
                    }
                }
            }
        }
        return success;
    }

    private BluetoothGattCharacteristic findNotifyCharacteristic(BluetoothGattService service, UUID characteristicUUID) {
        BluetoothGattCharacteristic characteristic = null;
        List<BluetoothGattCharacteristic> characteristics = service.getCharacteristics();
        for (BluetoothGattCharacteristic c : characteristics) {
            if ((c.getProperties() & BluetoothGattCharacteristic.PROPERTY_NOTIFY) != 0 && characteristicUUID.equals(c.getUuid())) {
                characteristic = c;
                break;
            }
        }
        if (characteristic != null) {
            return characteristic;
        }
        for (BluetoothGattCharacteristic c : characteristics) {
            if ((c.getProperties() & BluetoothGattCharacteristic.PROPERTY_INDICATE) != 0 && characteristicUUID.equals(c.getUuid())) {
                characteristic = c;
                break;
            }
        }
        return characteristic;
    }

然后只需在onServicesDiscovered()方法中调用这个方法即可

enableNotification(bluetoothGatt,serviceNotifyUUID, notifyUUID);
            serviceNotifyUUID为服务ID，notifyUUID为notify的UUID