在片段中初始化映射

Question

我在初始化我的映射時遇到問題。地圖片段被充滿到主要活動的FrameLayout中。我一直在setUpMapIfNeeded（）方法中得到一個空指針異常。

activity_main.xml中

<LinearLayout 
      android:layout_width="fill_parent" 
      android:layout_height="fill_parent" 
      android:orientation="vertical"> 

`   
     <include layout="@layout/toolbar"/> 

     <FrameLayout 
       android:id="@+id/frameLayout" 
       android:layout_width="fill_parent" 
       android:layout_height="fill_parent"></FrameLayout> 
    </LinearLayout> 



    <android.support.design.widget.NavigationView 
      android:id="@+id/navigation_view" 
      android:layout_height="match_parent" 
      android:layout_width="wrap_content" 
      android:layout_gravity="start" 
      app:headerLayout="@layout/header" 
      app:menu="@menu/drawer" 
      /> 

</android.support.v4.widget.DrawerLayout> 

map_fragment.xml

<?xml version="1.0" encoding="utf-8"?> 
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" 
       xmlns:tools="http://schemas.android.com/tools" 
       android:orientation="vertical" 
       android:layout_width="match_parent" 
       android:layout_height="match_parent"> 


    <fragment 
      android:layout_width="match_parent" 
      android:layout_height="match_parent" 
      android:id="@+id/map" 
      tools:context=".MapFragment" 
      android:name="com.google.android.gms.maps.SupportMapFragment"/> 

</LinearLayout> 

MainActivity.java

switch (menuItem.getItemId()) { 
       case R.id.shop: 

        MapFragment mapFragment = new MapFragment(); 
        android.support.v4.app.FragmentTransaction fragmentTransaction = getSupportFragmentManager().beginTransaction(); 
        fragmentTransaction.replace(R.id.frameLayout,mapFragment); 
        fragmentTransaction.commit(); 

        break; 
       case R.id.list: 
        ListFragment listFragment = new ListFragment(); 
        android.support.v4.app.FragmentTransaction fragmentTransaction1 = getSupportFragmentManager().beginTransaction(); 
        fragmentTransaction1.replace(R.id.frameLayout,listFragment); 
        fragmentTransaction1.commit(); 

        break; 
       case R.id.points: 
        Toast.makeText(getApplicationContext(),"Global card selected",Toast.LENGTH_SHORT).show(); 
        break; 
      } 
      return true; 
     } 
    }); 

MapFragment.java

@Override 
public View onCreateView(LayoutInflater inflater, ViewGroup container, 
         Bundle savedInstanceState) { 
    View view = inflater.inflate(R.layout.map_fragment,container,false); 

    //Check if GPS is enabled 
    locationManager = (LocationManager)getActivity().getSystemService(Context.LOCATION_SERVICE); 
    if (locationManager.isProviderEnabled(LocationManager.GPS_PROVIDER)){ 
     Toast.makeText(getContext(),"GPS enabled",Toast.LENGTH_SHORT).show(); 
    }else { 
     showGPSDisabledAlertToUser(); 
    } 

    setUpMapIfNeeded(); 
    return view; 
} 

private void setUpMapIfNeeded() { 
    // Do a null check to confirm that we have not already instantiated the map. 
    if (mMap == null) { 
     // Try to obtain the map from the SupportMapFragment. 
     //I get a null pointer exception at this point, no map it gotten 
     mMap = ((SupportMapFragment)getActivity().getSupportFragmentManager().findFragmentById(R.id.map)) 
       .getMap(); 
     // Check if we were successful in obtaining the map. 
     if (mMap != null) { 
      setUpMap(); 
     } 
    } 
} 

Answer 1

看看我的回購mapTab here。它顯示瞭如何在片段中初始化Google地圖。

示例代碼：

public class MapTabFragment extends Fragment { 

    private SupportMapFragment mMapView; 

    public static MapTabFragment newInstance(String param1, String param2) { 
     MapTabFragment fragment = new MapTabFragment(); 
     return fragment; 
    } 

    MapView mapView; 
    GoogleMap map; 

    @Override 
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) { 
     View v = inflater.inflate(R.layout.fragment_map, container, false); 
     // Gets the MapView from the XML layout and creates it 

     MapsInitializer.initialize(getActivity()); 


     switch (GooglePlayServicesUtil.isGooglePlayServicesAvailable(getActivity())) { 
      case ConnectionResult.SUCCESS: 
       Toast.makeText(getActivity(), "SUCCESS", Toast.LENGTH_SHORT).show(); 
       mapView = (MapView) v.findViewById(R.id.map); 
       mapView.onCreate(savedInstanceState); 
       // Gets to GoogleMap from the MapView and does initialization stuff 
       if (mapView != null) { 
        map = mapView.getMap(); 
        map.getUiSettings().setMyLocationButtonEnabled(false); 
        map.setMyLocationEnabled(true); 
        CameraUpdate cameraUpdate = CameraUpdateFactory.newLatLngZoom(new LatLng(43.1, -87.9), 10); 
        map.animateCamera(cameraUpdate); 
       } 
       break; 
      case ConnectionResult.SERVICE_MISSING: 
       Toast.makeText(getActivity(), "SERVICE MISSING", Toast.LENGTH_SHORT).show(); 
       break; 
      case ConnectionResult.SERVICE_VERSION_UPDATE_REQUIRED: 
       Toast.makeText(getActivity(), "UPDATE REQUIRED", Toast.LENGTH_SHORT).show(); 
       break; 
      default: 
       Toast.makeText(getActivity(), GooglePlayServicesUtil.isGooglePlayServicesAvailable(getActivity()), Toast.LENGTH_SHORT).show(); 
     } 

     // Updates the location and zoom of the MapView 

     LatLng sydney = new LatLng(-33.867, 151.206); 

     map.setMyLocationEnabled(true); 
     map.moveCamera(CameraUpdateFactory.newLatLngZoom(sydney, 13)); 

     map.addMarker(new MarkerOptions() 
       .title("Sydney") 
       .snippet("The most populous city in Australia.") 
       .position(sydney)); 

     return v; 
    } 

    @Override 
    public void onResume() { 
     mapView.onResume(); 
     super.onResume(); 
    } 

    @Override 
    public void onDestroy() { 
     super.onDestroy(); 
     mapView.onDestroy(); 
    } 

    @Override 
    public void onLowMemory() { 
     super.onLowMemory(); 
     mapView.onLowMemory(); 
    } 
} 

XML此：

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android" 
       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" 
     android:name="com.bojie.materialtest.fragments.UpcomingFragment"/> 

</RelativeLayout>