蓝牙Ble通知回调发送命令之后没反应，onCharacteristicChanged

在发送命令之后，onCharacteristicChanged这个回调里面接收不到数据

打开通知

 /*打开广播通知*/
    private void notifyData() {
        BluetoothGattCharacteristic characteristic = bluetoothGatt.getService(N_Notify).getCharacteristic(uNotify);
        BluetoothGattDescriptor descriptor = characteristic.getDescriptor(UUID.fromString("00002902-0000-1000-8000-00805f9b34fb"));
        descriptor.setValue(BluetoothGattDescriptor.ENABLE_NOTIFICATION_VALUE);
        bluetoothGatt.writeDescriptor(descriptor);
        bluetoothGatt.setCharacteristicNotification(characteristic, true);
                ｝

发送数据

    public void writeData() {
        if (bluetoothGatt == null) {
            return;
        }
        BluetoothGattCharacteristic characteristic = bluetoothGatt.getService(N_Write).getCharacteristic(uWrite);
        characteristic.setValue("EF52FFFAFFFF");
        bluetoothGatt.writeCharacteristic(characteristic);
    }

接收通知

     @Override
        public void onCharacteristicChanged(BluetoothGatt gatt, BluetoothGattCharacteristic characteristic) {
            super.onCharacteristicChanged(gatt, characteristic);
            bluetoothGatt = gatt;
            byte[] value = characteristic.getValue();
            try {
                String s=new String(value,"UTF-8");
                Log.e(TAG, "onCharacteristicChanged: "+s);
            } catch (UnsupportedEncodingException e) {
                e.printStackTrace();
            }

            printNotify(value);
        }