android - ViewPager NullPointer 中的 MapFragment : 'void maps.ad.y.v()' on a null object reference

Question

我想在 Fragment 中有一个 MapView。看起来很简单……我还是不明白!

启动应用程序时出现此错误:

java.lang.NullPointerException: Attempt to invoke interface method 'void maps.ad.y.v()' on a null object reference

我有一个 ViewPager Activity :MainActivity

public class MainActivity extends AppCompatActivity {

  private SectionsPagerAdapter mSectionsPagerAdapter;
  private ViewPager mViewPager;

  //...onCreate(), etc

  public class SectionsPagerAdapter extends FragmentPagerAdapter {
    //...
    @Override
    public Fragment getItem(int position) {
      if (position == 0) {

        return ClassicFragment.newInstance(position + 1);
        // no problem with this one

      } else if (position == 1) {

        return MyMapFragment.newInstance(position + 1);
        // here is my problem

      }
    }
  }   
}

还有2个 fragment 。 (一个简单的，一个有 map 的)我无法正确制作的 fragment :MyMapFragment

public class MyMapFragment extends SupportMapFragment implements OnMapReadyCallback {

    View rootView;
    private MapView mapView;
    private GoogleMap googleMap;

    public MyMapFragment() {
    }

    public static MyMapFragment newInstance(int sectionNumber) {
        MyMapFragment fragment = new MyMapFragment();
        return fragment;
    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {
        rootView = inflater.inflate(R.layout.fragment_map, container, false);
        return rootView;
    }

    @Override
    public void onViewCreated(View view, Bundle savedInstanceState) {
        mapView = (MapView) rootView.findViewById(R.id.map);
        mapView.onCreate(savedInstanceState);
        mapView.onResume();
        mapView.getMapAsync(this);//when you already implement OnMapReadyCallback in your fragment
    }

    @Override
    public void onMapReady(GoogleMap map) {
        googleMap = map;
    }
}

最后，这是 MyMapFragment 的 xml (fragment_map.xml)。

<LinearLayout 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">

    <com.google.android.gms.maps.MapView
        android:id="@+id/map"
        android:layout_width="match_parent"
        android:layout_height="match_parent"/>

</LinearLayout>

知道我做错了什么吗？

Answer 1

我找到了 2 个解决方案:

解决方案一:

将 SupportMapFragment 更改为 Fragment。

方案二:(我选择了这个)

在 MyMapFragment 中添加此调用。

super.onCreateView(inflater, container, savedInstanceState);