如何获得对用Java创建的GoogleMap对象的引用？

Question

我试图获得对创建java的GoogleMap对象的引用，但我不知道如何获得这个引用。

        LinearLayout mapLayout = new LinearLayout(customToursActivity);
        mapLayout.setId(generateViewId(rootView));
        int mapLayoutHeight = Math.round(getResources().getDimension(R.dimen.custom_tour_list_map_size));
        mapLayout.setLayoutParams(new LinearLayout.LayoutParams(LinearLayout.LayoutParams.MATCH_PARENT, mapLayoutHeight));
        layout.addView(mapLayout);

        FragmentManager fm = getChildFragmentManager();
        SupportMapFragment supportMapFragment =  SupportMapFragment.newInstance();
        fm.beginTransaction().replace(mapLayout.getId(), supportMapFragment).commit();
        GoogleMap mMap = supportMapFragment.getMap();
        mMap.setMyLocationEnabled(true);

01-23 17:09:54.168    3795-3795/abff.googlemapsappteste E/AndroidRuntime﹕ FATAL EXCEPTION: main
    Process: abff.googlemapsappteste, PID: 3795
    java.lang.NullPointerException: Attempt to invoke virtual method 'void com.google.android.gms.maps.GoogleMap.setMyLocationEnabled(boolean)' on a null object reference
            at abff.googlemapsappteste.CustomToursList.createPlacemarksList(CustomToursList.java:458)
            at abff.googlemapsappteste.CustomToursList.onCreateView(CustomToursList.java:73)
            at android.support.v4.app.Fragment.performCreateView(Fragment.java:1789)
            at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:955)
            at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1138)
            at android.support.v4.app.BackStackRecord.run(BackStackRecord.java:740)
            at android.support.v4.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:1501)
            at android.support.v4.app.FragmentManagerImpl.executePendingTransactions(FragmentManager.java:490)
            at android.support.v4.app.FragmentPagerAdapter.finishUpdate(FragmentPagerAdapter.java:141)
            at android.support.v4.view.ViewPager.populate(ViewPager.java:1105)
            at android.support.v4.view.ViewPager.populate(ViewPager.java:951)
            at android.support.v4.view.ViewPager.onMeasure(ViewPager.java:1473)
            at android.view.View.measure(View.java:17637)
            at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5536)
            at android.widget.FrameLayout.onMeasure(FrameLayout.java:436)
            at android.support.v7.internal.widget.ContentFrameLayout.onMeasure(ContentFrameLayout.java:124)
            at android.view.View.measure(View.java:17637)
            at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5536)
            at android.support.v7.internal.widget.ActionBarOverlayLayout.onMeasure(ActionBarOverlayLayout.java:444)
            at android.view.View.measure(View.java:17637)
            at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5536)
            at android.widget.FrameLayout.onMeasure(FrameLayout.java:436)
            at android.view.View.measure(View.java:17637)
            at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5536)
            at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1436)
            at android.widget.LinearLayout.measureVertical(LinearLayout.java:722)
            at android.widget.LinearLayout.onMeasure(LinearLayout.java:613)
            at android.view.View.measure(View.java:17637)
            at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5536)
            at android.widget.FrameLayout.onMeasure(FrameLayout.java:436)
            at com.android.internal.policy.impl.PhoneWindow$DecorView.onMeasure(PhoneWindow.java:2618)
            at android.view.View.measure(View.java:17637)
            at android.view.ViewRootImpl.performMeasure(ViewRootImpl.java:2019)
            at android.view.ViewRootImpl.measureHierarchy(ViewRootImpl.java:1177)
            at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:1383)
            at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:1065)
            at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:5901)
            at android.view.Choreographer$CallbackRecord.run(Choreographer.java:767)
            at android.view.Choreographer.doCallbacks(Choreographer.java:580)
            at android.view.Choreographer.doFrame(Choreographer.java:550)
            at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:753)
            at android.os.Handler.handleCallback(Handler.java:739)
            at android.os.Handler.dispatchMessage(Handler.java:95)
            at android.os.Looper.loop(Looper.java:211)
            at android.app.ActivityThread.main(ActivityThread.java:5389)
            at java.lang.reflect.Method.invoke(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:372)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1020)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:815)

Answer 1

有几种方法可以做到这一点。

1）.如果您的目标是API级别12之后的应用程序，那么您可以简单地使用MapFragment而不是SupportMapFragment。下面是如何将MapFragment添加到fragment并获取对GoogleMap对象的引用的示例代码。

 Map mapFragment = MapFragment.newInstance();
 FragmentTransaction fragmentTransaction =
         getChildFragmentManager().beginTransaction();
 fragmentTransaction.replace(mapLayout.getId(), mapFragment).commit();

然后使用getMapAsync()设置片段的回调。

mapFragment.getMapAsync(this); // your fragment need to implement `OnMapReadyCallback`

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

你可以在这里查阅官方文件

2）但是，如果您的目标应用程序早于API级别12，或者出于某种原因仍然希望使用SupportMapFragment，那么您还可以使用两个Otpions。

a）。由于映射初始化是异步的，所以您必须等待supportMapFragment.oncreateView()被调用，这基本上是在您的片段onActivityCreated()之后，在onActivityCreated()之前。因此，如果您将supportMapFragment添加到onActivityCreated()内部的事务中，那么您将在onStart()或

public class MyFragment extends Fragment {

    private SupportMapFragment mSupportMapFragment;
    private GoogleMap mGoogleMap;

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
        return inflater.inflate(R.layout.layout_with_map, container, false);
    }

    @Override
    public void onActivityCreated(Bundle savedInstanceState) {
        super.onActivityCreated(savedInstanceState);
        FragmentManager fm = getChildFragmentManager();
        mSupportMapFragment =  SupportMapFragment.newInstance();
        fm.beginTransaction().replace(mapLayout.getId(),mSupportMapFragment).commit();
    }

    @Override
    public void onResume() {
        super.onResume();
        if (mGoogleMap == null) {
            mGoogleMap = mSupportMapFragment.getMap();
        }
    }
}

如果您面临任何IllegalStateException（Google bug中跟踪的问题），只需override您的片段ondetach()

@Override
public void onDetach() {
    super.onDetach();
    try {
        Field childFragmentManager = Fragment.class
                .getDeclaredField("mChildFragmentManager");
        childFragmentManager.setAccessible(true);
        childFragmentManager.set(this, null);
    } catch (NoSuchFieldException e) {
        throw new RuntimeException(e);
    } catch (IllegalAccessException e) {
        throw new RuntimeException(e);
    }
}

您可以重写SupportMapFragment的onActivityCreated()。

public class MyFragment extends Fragment {

        private SupportMapFragment mSupportMapFragment;
        private GoogleMap mGoogleMap;

 @Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
    View view = inflater.inflate(R.layout.layout_with_map, container, false);
    mSupportMapFragment = new SupportMapFragment() {
        @Override
        public void onActivityCreated(Bundle savedInstanceState) {
            super.onActivityCreated(savedInstanceState);
            mGoogleMap = mSupportMapFragment.getMap();
            if (mGoogleMap != null) {
               mGoogleMap.setMyLocationEnabled(true);
            }
        }
    };
    getChildFragmentManager().beginTransaction().replace(mapLayout.getId(), mSupportMapFragment).commit();;
    return view;   
   }
}