MapsActivity为主要活动时，导航抽屉菜单项不起作用

Question

当单击菜单项时，没有任何反应。

public class MapsActivity extends AppCompatActivity implements OnMapReadyCallback, NavigationView.OnNavigationItemSelectedListener {
    private DrawerLayout drawerLayout;
    private GoogleMap mMap;


    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_maps);
        Toolbar toolbar = findViewById(R.id.toolbar);

        setSupportActionBar(toolbar);
        ActionBar actionbar = getSupportActionBar();
        actionbar.setDisplayHomeAsUpEnabled(true);
        actionbar.setHomeAsUpIndicator(R.drawable.ic_menu);
        drawerLayout = findViewById(R.id.drawer_layout);
        ActionBarDrawerToggle toggle = new ActionBarDrawerToggle(
                this, drawerLayout, toolbar, R.string.navigation_drawer_open, R.string.navigation_drawer_close);


        NavigationView navigationView = (NavigationView) findViewById(R.id.nav_view);
        navigationView.setNavigationItemSelectedListener(this);

抽屉和地图活动都是单个Java类。

    // Obtain the SupportMapFragment and get notified when the map is ready to be used.
    SupportMapFragment mapFragment = (SupportMapFragment) getSupportFragmentManager()
            .findFragmentById(R.id.map);
    mapFragment.getMapAsync(this);

---

这是用于从抽屉菜单中选择项目的代码。

@Override
public boolean onNavigationItemSelected(MenuItem item) {
    // Handle navigation view item clicks here.
    int id = item.getItemId();

    if (id == R.id.a1) {
        // Handle the camera action
        Toast.makeText(MapsActivity.this, "Signed in!", Toast.LENGTH_SHORT).show();


    } else if (id == R.id.Vehicle) {

    } else if (id == R.id.Settings) {

    } else if (id == R.id.nav_share) {

    } else if (id == R.id.nav_about) {

    }

    DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
    drawer.closeDrawer(GravityCompat.START);
    return true;
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
    switch (item.getItemId()) {
        case android.R.id.home:
            drawerLayout.openDrawer(GravityCompat.START);
            return true;
    }
    return super.onOptionsItemSelected(item);
}

---

地图从这里开始。

/**
 * Manipulates the map once available.
 * This callback is triggered when the map is ready to be used.
 * This is where we can add markers or lines, add listeners or move the camera. In this case,
 * we just add a marker near Sydney, Australia.
 * If Google Play services is not installed on the device, the user will be prompted to install
 * it inside the SupportMapFragment. This method will only be triggered once the user has
 * installed Google Play services and returned to the app.
 */
@Override
public void onMapReady(GoogleMap googleMap) {
    mMap = googleMap;

    // Add a marker in Sydney and move the camera
    LatLng sydney = new LatLng(-34, 151);
    mMap.addMarker(new MarkerOptions().position(sydney).title("Marker in Sydney"));
    mMap.moveCamera(CameraUpdateFactory.newLatLng(sydney));
}
}