Question

我有一个基于Google Maps的应用程序，并且正在使用方法getMap（），现在使用的是新模型getMapAsync，当我想清除或一般使用GoogleMap对象时遇到麻烦

java.lang.NullPointerException：尝试在空对象引用上调用虚拟方法'void com.google.android.gms.maps.GoogleMap.clear（）'。

我正在使用片段。

  @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {

        View view = inflater.inflate(R.layout.fragment_passenger_page1,
                container, false);
        MapFragment fm = (MapFragment) mainActivity.getFragmentManager().findFragmentById(R.id.map);
        fm.getMapAsync(this);
...
}

问题在我使用时就在这里

   @Override
    public void onResume() {

mMap.clear();

        if (listMarkers.size() > 0)

        {
            setMarker(listMarkers);
        }
        super.onResume();

    }

每次打开应用程序时都会调用此函数，并说mMap为null。

请帮助我。

Answer 1

请实现OnMapReadyCallback接口并覆盖

 @Override
 public void onMapReady(GoogleMap googleMap) {
    this.googleMap = googleMap;
    googleMap.clear()
    if (listMarkers.size() > 0)

    {
        setMarker(listMarkers);
    }


 }

并从简历方法中删除代码

Answer 2

thanks for your comments, I solved my problem by calling a clear() function in onResume, checking if the GoogleMap exists and if not creating it and passing to mMap.

 @Override
public void onResume() {

    clear();
    if (listMarkers.size() > 0)

    {
        setMarker(listMarkers);
    }
    super.onResume();

}

The clear function looks like:

public void clear() {

    GoogleMap gm = createMap();
    if (gm == null) {
        Log.e("clear", "The map is null"); //for testing purposes
        return;

    } else {
        Log.e("clear", "The map already exists"); //for testing purposes
        mMap = gm;
        mMap.clear();
    }


    startLocation = null;
    endLocation = null;
    txtFrom.setText("");
    txtTo.setText("");

}

And finally the createMap():

 private GoogleMap createMap() {

    if (mMap != null) {
        Log.e("create", "The map already exists"); // for testing purposes
        return mMap;
    }
    MapFragment fm = (MapFragment) 
    mainActivity.getFragmentManager().findFragmentById(R.id.map);
    try {
        fm.getMapAsync(this);
    } catch (Exception ex) {
        Log.e("Error", ex.getLocalizedMessage());
    }

    return null;

}

So in this way I always create a new GoogleMap if it doesn't exists.

If i'm doing something wrong don't hesitate to tell me :)

我在空对象引用上获取GoogleMap.clear

2 个答案: