mapFragment.getMap（）返回null [英] mapFragment.getMap() returns null

问题描述

我想从一个SupportMapFragment的地图，但它返回null。从我读这可能是因为该片段尚未完全显示出来，因此没有地图存在？我试着用executePendingTransactions（），但没有成功，到目前为止修复它。

任何想法如何解决这个问题？

下面是code

 私人GoogleMap的地图;
私人SupportMapFragment mapFragment;
@覆盖
公共无效的onCreate（包savedInstanceState）{

    // ...
    super.onCreate（savedInstanceState）;
    的setContentView（R.layout.screen_mission2）;
    GoogleMapOptions mapOptions =新GoogleMapOptions（）;

    mapOptions.mapType（GoogleMap.MAP_TYPE_NORMAL）
        .compassEnabled（真）
        .rotateGesturesEnabled（假）
        .tiltGesturesEnabled（假）;

    android.support.v4.app.FragmentManager myFragmentManager = getSupportFragmentManager（）;
    android.support.v4.app.FragmentManager.enableDebugLogging（真正的）;
    mapFragment = SupportMapFragment.newInstance（mapOptions）;
    FragmentTransaction fragmentTransaction = myFragmentManager.beginTransaction（）;
    fragmentTransaction.add（R.id.mapFragment，mapFragment）;
    fragmentTransaction.commit（）;
    myFragmentManager.executePendingTransactions（）;

    如果（mapFragment == NULL）Base.log（mapFragment ==空）;
    如果（图== NULL）{
        地图= mapFragment.getMap（）;
        Base.log（地图应已初始化）;
        如果（图== NULL）Base.log（图还是空）;
    }
}
 

和布局文件：

 ＆LT;片段
    机器人：ID =@ + ID / mapFragment
    机器人：名称=com.google.android.gms.maps.SupportMapFragment
    机器人：layout_width =match_parent
    机器人：layout_height =match_parent/＆GT;
 

它返回以下日志

  V / FragmentManager（24224）：地址：SupportMapFragment {4078c4b8 ID = 0x7f06003d}
V / FragmentManager（24224）：分配的片段指数SupportMapFragment {4078c4b8＃1 ID = 0x7f06003d}
V / FragmentManager（24224）：通过MoveTo创建：SupportMapFragment {4078c4b8＃1 ID = 0x7f06003d}
D / EMR（24224）：图应该已经初始化
D / EMR（24224）：图仍空
 

解决方案

尝试将所有code引用您的 GoogleMap的到 ONSTART（ ）或 onResume（）。地图中的片段，该地图是没有实例化后才片段已经通过 onCreateView 走了（<一href="https://developers.google.com/maps/documentation/android/reference/com/google/android/gms/maps/MapFragment#getMap%28%29">link),这恰好经过父活动已经走过的onCreate（）。另外，你需要检查你的 GoogleMap的为<$不见了C C>空不管，因为如果谷歌播放服务没有安装，或者在地图无法使用某些其他原因，这将是空。

I'm trying to get a map from a SupportMapFragment but it returns null. From what I read this could be because the fragment is not yet fully displayed and therefore no map exists?! I tried fixing it using executePendingTransactions() but with no success so far.

Any ideas how to fix it?

Here is the code

private GoogleMap map;
private SupportMapFragment mapFragment;
@Override
public void onCreate( Bundle savedInstanceState ) {

    //...
    super.onCreate( savedInstanceState ); 
    setContentView( R.layout.screen_mission2 );
    GoogleMapOptions mapOptions = new GoogleMapOptions();

    mapOptions.mapType(GoogleMap.MAP_TYPE_NORMAL)
        .compassEnabled(true)
        .rotateGesturesEnabled(false)
        .tiltGesturesEnabled(false);

    android.support.v4.app.FragmentManager myFragmentManager = getSupportFragmentManager();
    android.support.v4.app.FragmentManager.enableDebugLogging(true);
    mapFragment = SupportMapFragment.newInstance(mapOptions);
    FragmentTransaction fragmentTransaction = myFragmentManager.beginTransaction();
    fragmentTransaction.add(R.id.mapFragment, mapFragment);
    fragmentTransaction.commit();
    myFragmentManager.executePendingTransactions();

    if(mapFragment == null) Base.log("mapFragment==null");
    if(map==null){
        map = mapFragment.getMap();
        Base.log("map should have been initialized");
        if(map==null) Base.log("map still null");
    }
}

And the layout file:

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

It returns the following log

V/FragmentManager(24224): add: SupportMapFragment{4078c4b8 id=0x7f06003d}
V/FragmentManager(24224): Allocated fragment index SupportMapFragment{4078c4b8 #1 id=0x7f06003d}
V/FragmentManager(24224): moveto CREATED: SupportMapFragment{4078c4b8 #1 id=0x7f06003d}
D/EMR     (24224): map should have been initialized
D/EMR     (24224): map still null

解决方案

Try moving all code that references your GoogleMap to onStart() or onResume(). The map in a map fragment isn't instantiated until after the fragment has gone through onCreateView (link), which happens after the parent activity has gone through onCreate(). Also, you need to check your GoogleMap for null regardless, because if google play services aren't installed, or the map isn't available for some other reason, it will be null.

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