尝试在 Google Map V2 上放置标记时出现 NullPointerException

Question

当我尝试使用 placeMarker 方法在谷歌地图上放置标记时，我得到 NullPointerException

NullPointerException: Attempt to invoke virtual method 'android.content.res.Resources android.content.Context.getResources()' on a null object reference`
I/DpmTcmClient: RegisterTcmMonitor from: org.apache.http.impl.conn.TcmIdleTimerMonitor
W/DynamiteModule: Local module descriptor class for com.google.android.gms.googlecertificates not found.
I/DynamiteModule: Considering local module com.google.android.gms.googlecertificates:0 and remote module com.google.android.gms.googlecertificates:2
I/DynamiteModule: Selected remote version of com.google.android.gms.googlecertificates, version >= 2
D/GoogleCertificates: com.google.android.gms.googlecertificates module is loaded
E/url: http://maps.googleapis.com/maps/api/geocode/json?latlng=35.7742618,51.3596331&sensor=true
E/Lat Long to Addresss:
E/Googlemap: null
D/GoogleCertificatesImpl: Fetched 363 Google certificates
I/b: Sending API token request.
E/b: Authentication failed on the server.
E/Google Maps Android API: Authorization failure
Ensure that the "Google Maps Android API v2" is enabled.
                                                                                 Ensure that the following Android Key exists:

我还使用了 getAsyncMap 和 OnMapReady()。在 OnMapReady 内部我调用了一个 Asynktask 来获取用户位置并调用了 onPostExecute placeMarker 方法：

public void placeMarker(LatLongDetails user_latlongobj2,
final Context contextPlace) {


try {
if (googlemap == null) {
    intialiseMap();
    animatecamera(user_latlongobj);
}
if (LoginDetails.Address.length() < 1) {
    LoginDetails.Address = "Getting your location .....";
}
googlemap.clear();
marker = new MarkerOptions().position(
        new LatLng(user_latlongobj2.user_latitude,
                user_latlongobj2.user_longitude)).title(
        LoginDetails.Address);

System.out.println("This is the Address" + LoginDetails.Address);

marker.icon(BitmapDescriptorFactory.fromResource(R.drawable.marker));


googlemap.addMarker(marker).showInfoWindow();
System.out.println("PLACING MARKER" + LoginDetails.Address);
if (marker == null || contextPlace == null) {
    Intent in =new Intent(this,ProfileActivity1.class);
    in.setFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
    in.setFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP); 
    startActivity(in);
}
else
fixmarker(marker, contextPlace);

} catch (Exception e) {
fixmarker(marker, contextPlace);
Log.d("Profileactivity", "" + e);
  } 

}

当我尝试将 getMap() 更改为 getAsyncMap() 时，所有这些问题都出现了另外请检查 link 和 GitHub 上的完整整个活动

我删除了 try 和 catch 以查找有关错误的更多详细信息。这里是 logcat：

enter code herejava.lang.NullPointerException: Attempt to invoke virtual method 'android.content.res.Resources android.content.Context.getResources()' on a null object reference
                                                                            at android.content.ContextWrapper.getResources(ContextWrapper.java:87)
                                                                            at android.view.ContextThemeWrapper.getResources(ContextThemeWrapper.java:81)
                                                                            at android.support.v7.app.AppCompatActivity.getResources(AppCompatActivity.java:551)
                                                                            at android.content.Context.getString(Context.java:413)
                                                                            at com.example.cabbookinghome.ProfileActivity1.intialiseMap(ProfileActivity1.java:280)
                                                                            at com.example.cabbookinghome.ProfileActivity1.placeMarker(ProfileActivity1.java:327)
                                                                            at epbit.helper.ConversionTaskLatLonLoc.onPostExecute(ConversionTaskLatLonLoc.java:130)
                                                                            at epbit.helper.ConversionTaskLatLonLoc.onPostExecute(ConversionTaskLatLonLoc.java:24)
                                                                            at android.os.AsyncTask.finish(AsyncTask.java:651)
                                                                            at android.os.AsyncTask.access$500(AsyncTask.java:180)
                                                                            at android.os.AsyncTask$InternalHandler.handleMessage(AsyncTask.java:668)
                                                                            at android.os.Handler.dispatchMessage(Handler.java:102)

Answer 1

经过 3 天的搜索和处理，终于奏效了。真正的问题是 googlemap 为 null，这意味着地图未加载。我使用了 try 和 catch，但您永远不应该只捕获和异常而什么都不做。 记录异常后，检查我发现的日志：

com.google.android.gms.maps.MapFragment.getMap()' on a null object reference

首先我尝试了这个链接Google Map returning nullpointerexception Google Maps Android V2

googleMap = ((SupportMapFragment) getChildFragmentManager().findFragmentById(R.id.map)).getMap();

然后 getChildFragmentManager 变为红色表示 getChildFragmentManager () 无法解析或无法引用。使用 getSupportFragmentManager() 代替此链接中所述 (getChildFragmentManager () cannot be resolved or cannot be referenced) 终于解决了问题，地图已经加载完毕

googlemap = ((SupportMapFragment) getSupportFragmentManager().findFragmentById(R.id.mapfragment)).getMap();

请注意，如果您的类从AppCompatActivity扩展，那么您需要使用getSupportFragmentManager() 因为getChildFragmentManager() 是无法从AppCompatActivity 访问的片段的方法

Answer 2

这是因为 google map 对象在 if 语句之后被清除。删除 googlemap.clear() 并尝试。

Answer 3

您的地图未初始化或未获取您的位置。检查位置传感器是否处于活动状态。如果没有，请激活它。你可以试试这个代码。

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.
            mMap = ((SupportMapFragment) getSupportFragmentManager().findFragmentById(R.id.map))
                    .getMap();
            // Check if we were successful in obtaining the map.
            if (mMap != null) {
                setUpMap();
            }
        }
    }

    private void setUpMap() {
        mMap.addMarker(new MarkerOptions().position(new LatLng(0, 0)).title("Marker"));
        mMap.setMyLocationEnabled(true);


    }