Teil der MainActivity

public class MainActivity extends AppCompatActivity {

    private AppBarConfiguration mAppBarConfiguration;

    private final static int REQUEST_ENABLE_BT = 1;
    BluetoothAdapter bluetoothAdapter = BluetoothAdapter.getDefaultAdapter();
    private ConnectionViewModel connectionViewModel;
    private BluetoothAdapter adapter = null;
    private BluetoothSocket socket = null;
    private static String mac_adresse = "98:D3:31:FC:34:19";
    private UUID uuid = UUID.fromString("00001101-0000-1000-8000-00805F9B34FB");
    public boolean is_connected = false;
    private static final String LOG_TAG = "";
    private OutputStream stream_out = null;
    private InputStream stream_in = null;
    Switch s;
    TextView t;
    TextView t2;
    Button b;
    double value;


    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        connectionViewModel =
                ViewModelProviders.of(this).get(ConnectionViewModel.class);

        Toolbar toolbar = findViewById(R.id.toolbar);
        setSupportActionBar(toolbar);
        //controls the switching between the fragments with the
        //navigation view
        DrawerLayout drawer = findViewById(R.id.drawer_layout);
        NavigationView navigationView = findViewById(R.id.nav_view);
        // Passing each menu ID as a set of Ids because each
        // menu should be considered as top level destinations.
        mAppBarConfiguration = new AppBarConfiguration.Builder(
                R.id.nav_home, R.id.nav_history, R.id.nav_map,
                R.id.nav_settings, R.id.nav_share, R.id.nav_datagetting, R.id.nav_connection)
                .setDrawerLayout(drawer)
                .build();
        NavController navController = Navigation.findNavController(this, R.id.nav_host_fragment);
        NavigationUI.setupActionBarWithNavController(this, navController, mAppBarConfiguration);
        NavigationUI.setupWithNavController(navigationView, navController);

        //transfer of the data from the connection fragment to history fragment//





        //////////////////////////////////////////////////////////////////////////
        int MyVersion = Build.VERSION.SDK_INT;
        if (MyVersion > Build.VERSION_CODES.LOLLIPOP_MR1) {
            if (!checkIfAlreadyhavePermission()) {
                requestForSpecificPermission();
            }
        }

    }