java - getSupportFragmentManager().findFragmentById() 总是返回 null

Question

我试图在我的应用程序中显示 GoogleMap，但我在这项任务开始时遇到了问题。线路:

SupportMapFragment mapFrag = (SupportMapFragment) getActivity().getSupportFragmentManager().findFragmentById(R.id.map);

总是返回 null。

我尝试了很多东西，但没有任何效果。你能帮我找出问题所在吗？

这是我的代码:

public class MapSectionFragment extends Fragment implements
    ConnectionCallbacks,
    OnConnectionFailedListener,
    LocationListener,
    OnMyLocationButtonClickListener,
    OnMapReadyCallback{

    private GoogleMap map;
    Location location;
    GoogleApiClient mGoogleApiClient;

    private static final LocationRequest REQUEST = LocationRequest.create()
        .setInterval(5000)         // 5 seconds
        .setFastestInterval(16)    // 16ms = 60fps
        .setPriority(LocationRequest.PRIORITY_HIGH_ACCURACY);

    private void createMapView(){
        try{
            //here it comes
            SupportMapFragment mapFrag = (SupportMapFragment) getActivity().getSupportFragmentManager().findFragmentById(R.id.map);

            map = mapFrag.getMap(); //throws NullPointerException
        }
    }

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

        View rootView = inflater.inflate(R.layout.fragment_section_map,
            container, false);

        createMapView();

        return rootView;
    }

    @Override
    public void onPause() {
        super.onPause();
        mGoogleApiClient.disconnect();
    }

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

    @Override
    public void onConnected(Bundle bundle) {
    LocationServices.FusedLocationApi.requestLocationUpdates(
            mGoogleApiClient,
            REQUEST,
            this);  // LocationListener
    }

    @Override
    public void onConnectionSuspended(int i) {

    }

    @Override
    public void onLocationChanged(Location location) {

    }

    @Override
    public void onConnectionFailed(ConnectionResult connectionResult) {

    }

    @Override
    public void onMapReady(GoogleMap googleMap) {
        map.setMyLocationEnabled(true);
    }

    @Override
    public boolean onMyLocationButtonClick() {
        Toast.makeText(getActivity(), "MyLocation button clicked", Toast.LENGTH_SHORT).show();
        // Return false so that we don't consume the event and the default behavior still occurs
        // (the camera animates to the user's current position).
    return false;
    }
}

这是带有 mapID 的 XML“fragment_section_map”:

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
   xmlns:tools="http://schemas.android.com/tools"
   android:orientation="vertical"
   android:layout_width="fill_parent"
   android:layout_height="fill_parent">


    <Button
        android:id="@+id/refresh_map_button"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:layout_marginBottom="16dp"
        android:text="@string/refresh_map" />

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

</LinearLayout>

感谢您的帮助!

Answer 1

请试试这个替换

SupportMapFragment mapFrag = (SupportMapFragment) getActivity().getSupportFragmentManager().findFragmentById(R.id.map);

与

SupportMapFragment mapFrag = (SupportMapFragment) getChildFragmentManager().findFragmentById(R.id.map);

因为

getChildFragmentManager()

将在 fragment 内管理 fragment ，因为您在 fragment 内使用 SupportMapFragment，所以请尝试此解决方案

希望对你有帮助