尝试在空对象引用上调用虚拟方法'void android.widget.LinearLayout.setVisibility（int）'

Question

我有一个导航抽屉活动，我试图用另一个片段替换背景中显示的mapFragment。该应用程序总是崩溃。

抽屉式导航活动：

package georgia.languagelandscape; 

//import android.app.FragmentManager; 
import android.net.Uri; 
import android.os.Bundle; 
import android.support.design.widget.FloatingActionButton; 
import android.support.design.widget.NavigationView; 
import android.support.design.widget.Snackbar; 
import android.support.v4.app.FragmentManager; 
import android.support.v4.app.FragmentTransaction; 
import android.support.v4.view.GravityCompat; 
import android.support.v4.widget.DrawerLayout; 
import android.support.v7.app.ActionBarDrawerToggle; 
import android.support.v7.app.AppCompatActivity; 
import android.support.v7.widget.Toolbar; 
import android.view.Menu; 
import android.view.MenuItem; 
import android.view.View; 
import android.widget.LinearLayout; 

public class NavigationDrawerActivity extends AppCompatActivity 
     implements NavigationView.OnNavigationItemSelectedListener, ProfileFragment.OnFragmentInteractionListener, ReplaceFragment.OnFragmentInteractionListener{ 

    MapFragment mapFragment= new MapFragment(); 
    FragmentManager fm = getSupportFragmentManager(); 

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

     FloatingActionButton fab = (FloatingActionButton) findViewById(R.id.fab); 
     fab.setOnClickListener(new View.OnClickListener() { 
      @Override 
      public void onClick(View view) { 
       Snackbar.make(view, "Replace with your own action", Snackbar.LENGTH_LONG) 
         .setAction("Action", null).show(); 
      } 
     }); 

     DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout); 
     ActionBarDrawerToggle toggle = new ActionBarDrawerToggle(
       this, drawer, toolbar, R.string.navigation_drawer_open, R.string.navigation_drawer_close); 
     drawer.setDrawerListener(toggle); 
     toggle.syncState(); 

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

     //me 
     navigationView.setItemIconTintList(null); 
     getSupportActionBar().setDisplayShowTitleEnabled(false); 


     FragmentTransaction ft = fm.beginTransaction(); 
     ft.replace(R.id.content_replace, mapFragment); 
     ft.commit(); 
    } 

    @Override 
    public void onBackPressed() { 
     DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout); 
     if (drawer.isDrawerOpen(GravityCompat.START)) { 
      drawer.closeDrawer(GravityCompat.START); 
     } else { 
      super.onBackPressed(); 
     } 
    } 

    @Override 
    public boolean onCreateOptionsMenu(Menu menu) { 
     // Inflate the menu; this adds items to the action bar if it is present. 
     getMenuInflater().inflate(R.menu.navigation_drawer, menu); 
     return true; 
    } 

    @Override 
    public boolean onOptionsItemSelected(MenuItem item) { 
     // Handle action bar item clicks here. The action bar will 
     // automatically handle clicks on the Home/Up button, so long 
     // as you specify a parent activity in AndroidManifest.xml. 
     int id = item.getItemId(); 

     //noinspection SimplifiableIfStatement 
     if (id == R.id.action_settings) { 
      return true; 
     } 

     return super.onOptionsItemSelected(item); 
    } 

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


     FragmentTransaction ft = fm.beginTransaction(); 

     ReplaceFragment replaceFragment=new ReplaceFragment(); 
     ft.replace(R.id.content_replace, replaceFragment); 

     if (id == R.id.nav_feed) { 
      // Handle the camera action 
     } else if (id == R.id.nav_my_profile) { 
      LinearLayout map_layout=(LinearLayout)this.findViewById(R.id.dummyLayout); 
      map_layout.setVisibility(1); 
      fm.beginTransaction().hide(fm.findFragmentById(R.id.mapView)).commit(); 
      // fm.beginTransaction().hide(getSupportFragmentManager().findFragmentById(mapFragment)).commit(); 
      //fm.beginTransaction().hide(getSupportFragmentManager().findFragmentById(‌​mapFragment)).c‌​ommit(); 
      //or getSupportFragmentManager().findFragmentById(R.id.mapFragmen‌​t).getView().setVisi‌​bility(View.INVISIBL‌​E); 
      ProfileFragment profileFragment= new ProfileFragment(); 
      ft.replace(R.id.content_replace, profileFragment); 

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

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

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

     } 

     ft.commit(); 

     DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout); 
     drawer.closeDrawer(GravityCompat.START); 
     return true; 
    } 

    @Override 
    public void onFragmentInteraction(Uri uri) { 

    } 

} 

MapFragment：

package georgia.languagelandscape; 

//import android.app.Fragment; 

import android.support.v4.app.Fragment; 
import android.os.Bundle; 
import android.view.LayoutInflater; 
import android.view.View; 
import android.view.ViewGroup; 

import com.google.android.gms.maps.CameraUpdateFactory; 
import com.google.android.gms.maps.GoogleMap; 
import com.google.android.gms.maps.MapView; 
import com.google.android.gms.maps.MapsInitializer; 
import com.google.android.gms.maps.OnMapReadyCallback; 
import com.google.android.gms.maps.SupportMapFragment; 
import com.google.android.gms.maps.model.BitmapDescriptorFactory; 
import com.google.android.gms.maps.model.CameraPosition; 
import com.google.android.gms.maps.model.LatLng; 
import com.google.android.gms.maps.model.MarkerOptions; 

//import android.support.v4.app.Fragment; 


/** 
* A simple {@link Fragment} subclass. 
* Activities that contain this fragment must implement the 
* {@link MapFragment.OnFragmentInteractionListener} interface 
* to handle interaction events. 
* Use the {@link MapFragment#newInstance} factory method to 
* create an instance of this fragment. 
*/ 
public class MapFragment extends SupportMapFragment implements OnMapReadyCallback { 

    private GoogleMap mGoogleMap; 

    @Override 
    public void onResume() { 
     super.onResume(); 
     if (mGoogleMap == null) { 
      getMapAsync(this); 
     } 
    } 

    @Override 
    public void onMapReady(GoogleMap googleMap) { 
     mGoogleMap = googleMap; 
     // latitude and longitude 
     double latitude = 17.385044; 
     double longitude = 78.486671; 

     // create marker 
     MarkerOptions marker = new MarkerOptions().position(
       new LatLng(latitude, longitude)).title("Hello Maps"); 

     // Changing marker icon 
     marker.icon(BitmapDescriptorFactory 
       .defaultMarker(BitmapDescriptorFactory.HUE_ROSE)); 

     // adding marker 
     googleMap.addMarker(marker); 
     CameraPosition cameraPosition = new CameraPosition.Builder() 
       .target(new LatLng(17.385044, 78.486671)).zoom(12).build(); 
     googleMap.animateCamera(CameraUpdateFactory 
       .newCameraPosition(cameraPosition)); 
    } 
} 

而且地图片段布局：

<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android" 
    xmlns:tools="http://schemas.android.com/tools" 
    android:layout_width="match_parent" 
    android:layout_height="match_parent" 
    tools:context="georgia.languagelandscape.MapFragment"> 


    <LinearLayout 
     android:id="@+id/dummyLayout" 
     android:layout_width="fill_parent" 
     android:layout_height="fill_parent" 
     android:orientation="vertical" 
     android:visibility="gone" > 
     <fragment xmlns:android="http://schemas.android.com/apk/res/android" 
      android:name="com.google.android.gms.maps.SupportMapFragment" 
      android:id="@+id/mapView" 
      android:layout_width="match_parent" 
      android:layout_height="match_parent"/> 

    </LinearLayout> 
</FrameLayout> 

我试图做它没有的LinearLayout从XML文件，但它仍然不起作用。我不能使用销毁方法或其他任何东西，因为基本上我没有返回一个View。我怎样才能隐藏地图？

Answer 1

删除此行：

LinearLayout map_layout=(LinearLayout)this.findViewById(R.id.dummyLayout); 
map_layout.setVisibility(1); 
fm.beginTransaction().hide(fm.findFragmentById(R.id.mapView)).commit();