MapFragment返回空

Question

mMapFragment = (SupportMapFragment) getSupportFragmentManager()
                .findFragmentByTag(MAP_FRAGMENT_TAG);

        // We only create a fragment if it doesn't already exist.
        if (mMapFragment == null) {
          mMapFragment = SupportMapFragment.newInstance();


            // Then we add it using a FragmentTransaction.
            FragmentTransaction fragmentTransaction =
                    getSupportFragmentManager().beginTransaction();
            fragmentTransaction.add(MapLay.getId(), mMapFragment, MAP_FRAGMENT_TAG);
             fragmentTransaction.commit();


            mMap=mMapFragment.getMap();

通过此代码，映射是可见的，但无法访问映射。

mMap=mMapFragment.getMap()；显示空值错误如何修复

Answer 1

更新1: getMap()是废弃的

最好是使用getMapAsync()的MapFragment/SupportMapFragment方法。如何使用下面所示的方法(从它们的documentation复制)的示例。

import com.google.android.gms.maps.*;
import com.google.android.gms.maps.model.*;
import android.app.Activity;
import android.os.Bundle;

public class MapPane extends Activity implements OnMapReadyCallback {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.map_activity);

        MapFragment mapFragment = (MapFragment) getFragmentManager()
                .findFragmentById(R.id.map);
        mapFragment.getMapAsync(this);
    }

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

}

引用谷歌的MapFragment/SupportMapFragment

只有在加载了底层映射系统并且片段中的底层视图存在时，才能使用getMap()获取getMap。这个类会自动初始化地图系统和视图；但是，当它准备就绪时，您无法得到保证，因为这取决于Google服务APK的可用性。如果GoogleMap不可用，getMap()将返回null。

在您的代码中，您在提交GoogleMap后立即检索MapFragment。等待MapFragment完全加载到活动中，这样您就可以得到GoogleMap。

也许，您可以使用接口将GoogleMap从MapFragment传递到Activity，如下所示。

public class MyMapFragment extends SupportMapFragment
{
  private MapCallback callback;

  public void setMapCallback(MapCallback callback)
  {
    this.callback = callback;
  }

  public static interface MapCallback
  {
     public void onMapReady(GoogleMap map);
  }

  @Override public void onActivityCreated(Bundle savedInstanceState)
  {
     super.onActivityCreated(savedInstanceState);
     if(callback != null) callback.onMapReady(getMap());     
  }
}


public class MyActivity extends Activity implements MyMapFragment.MapCallback
{
   // .........
  @Override
  public void onCreate(Bundle onsavedInstanceState)
  {
        mMapFragment = (MyMapFragment) getSupportFragmentManager()
                .findFragmentByTag(MAP_FRAGMENT_TAG);

        // We only create a fragment if it doesn't already exist.
        if (mMapFragment == null) {
               mMapFragment = MyMapFragment.newInstance();

               mMapFragment.setMapCallback(this); // This activity will receive the Map object once the map fragment is fully loaded

               // Then we add it using a FragmentTransaction.
               FragmentTransaction fragmentTransaction =
                    getSupportFragmentManager().beginTransaction();
               fragmentTransaction.add(MapLay.getId(), mMapFragment, MAP_FRAGMENT_TAG);
               fragmentTransaction.commit();

         }
         else
         {
               mMapFragment.setMapCallback(this); // This activity will receive the Map object once the map fragment is fully loaded
         }

  @Override
  public void onMapReady(GoogleMap map)
  {
     // Do what you want to map
  }

}

Answer 2

进口部分

import com.google.android.gms.maps.GoogleMap;
import com.google.android.gms.maps.SupportMapFragment;

在oncreate内部

SupportMapFragment mapFragment = (SupportMapFragment)getSupportFragmentManager().findFragmentById(R.id.map); 
    mMap = mapFragment.getMap();

和Xml部分

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

确保你已经投入了

<meta-data android:name="com.google.android.maps.v2.API_KEY"
              android:value="api key"/> 

在你的<application></application>标签里。

并在显能者档案中给予这些许可

<permission
          android:name="packagename.permission.MAPS_RECEIVE"
          android:protectionLevel="signature"/>
    <uses-permission android:name="packagename.permission.MAPS_RECEIVE"/>
    <uses-permission android:name="android.permission.INTERNET"/>
    <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/>
    <uses-permission android:name="com.google.android.providers.gsf.permission.READ_GSERVICES"/>
    <uses-permission android:name="android.permission.ACCESS_COARSE_LOCATION"/>
    <uses-permission android:name="android.permission.ACCESS_FINE_LOCATION"/>
    <uses-permission android:name="android.permission.ACCESS_NETWORK_STATE"/>    
    <uses-feature
        android:glEsVersion="0x00020000"
        android:required="true"/>

Answer 3

您的xml应该有SupportMapFragment。

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