android - 在视图页面片段中显示地图 v2 NullPointerException

Question

两三天以来，我一直在尝试在视图页面中实施 google map v2。我只收到 NullPointerException 错误。我不知道我做错了什么。我想要的是在 2 个片段之间滑动两次，其中一个是地图。另一个片段只是一个文本视图（还不重要）。

这是我的代码：

public class MainActivity extends FragmentActivity {

SectionsPagerAdapter mSectionsPagerAdapter;

/**
 * The {@link ViewPager} that will host the section contents.
 */
ViewPager mViewPager;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.main);

    // Create the adapter that will return a fragment for each of the three
    // primary sections of the app.
    mSectionsPagerAdapter = new SectionsPagerAdapter(getSupportFragmentManager());

    // Set up the ViewPager with the sections adapter.
    mViewPager = (ViewPager) findViewById(R.id.pager);
    mViewPager.setAdapter(mSectionsPagerAdapter);

}

@Override
public boolean onCreateOptionsMenu(Menu menu) {
    // Inflate the menu; this adds items to the action bar if it is present.
    getMenuInflater().inflate(R.menu.main, menu);
    return true;
}}

FragmentPagerAdapter：

public class SectionsPagerAdapter extends FragmentPagerAdapter {

public SectionsPagerAdapter(FragmentManager fm) {
    super(fm);
}

@Override
public Fragment getItem(int position) {

    if (position < 1) {
        Test_Fragment f = new Test_Fragment(position);
        return f;
    }
    else {
        Fragment_Map f = new Fragment_Map(position);
        return f;
    }
}

@Override
public int getCount() {
    // Show 2 total pages.
    return 2;
}

@Override
public CharSequence getPageTitle(int position) {
    switch (position) {
    case 0:
        return "Test Fragment";
    case 1:
        return "Map Fragment";
    }
    return null;
}
      }

地图片段：

public class Fragment_Map extends Fragment {

GoogleMap mMap;

private int fragmentNR;

public Fragment_Map(int nr) {
    this.fragmentNR = nr;
}

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
    if (mMap == null) {
        // Try to obtain the map from the SupportMapFragment.
        mMap = ((SupportMapFragment)getFragmentManager().findFragmentById(R.id.map)).getMap();

        if (mMap != null) {
            setUpMap();
        }
    }
    return (RelativeLayout) inflater.inflate(R.layout.fragment_map, container, false);
}


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

main.xml 看起来像

<android.support.v4.view.ViewPager xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:id="@+id/pager"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context=".MainActivity" >

<android.support.v4.view.PagerTitleStrip
    android:id="@+id/pager_title_strip"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:layout_gravity="top"
    android:background="#33b5e5"
    android:paddingBottom="4dp"
    android:paddingTop="4dp"
    android:textColor="#fff" />

    </android.support.v4.view.ViewPager>

最后是 fragmentmap.xml

     <?xml version="1.0" encoding="utf-8"?>
     <RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
      xmlns:tools="http://schemas.android.com/tools"
      android:layout_width="match_parent"
      android:layout_height="match_parent">

      <fragment xmlns:android="http://schemas.android.com/apk/res/android"
        android:id="@+id/map"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        class="com.google.android.gms.maps.SupportMapFragment"/>

       </RelativeLayout>

来自 logcat 的错误消息显示：

     01-08 15:16:11.726: E/AndroidRuntime(781): FATAL EXCEPTION: main
     01-08 15:16:11.726: E/AndroidRuntime(781): java.lang.NullPointerException
     01-08 15:16:11.726: E/AndroidRuntime(781):  atswipe.views2.Fragment_Map.onCreateView(Fragment_Map.java:39)
     01-08 15:16:11.726: E/AndroidRuntime(781):     at android.support.v4.app.Fragment.performCreateView(Fragment.java:1460)
     01-08 15:16:11.726: E/AndroidRuntime(781):     at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:911)
     01-08 15:16:11.726: E/AndroidRuntime(781):     at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1088)
     01-08 15:16:11.726: E/AndroidRuntime(781):     at android.support.v4.app.BackStackRecord.run(BackStackRecord.java:682)
     01-08 15:16:11.726: E/AndroidRuntime(781):     at android.support.v4.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:1444)
     01-08 15:16:11.726: E/AndroidRuntime(781):     at android.support.v4.app.FragmentManagerImpl.executePendingTransactions(FragmentManager.java:461)
     01-08 15:16:11.726: E/AndroidRuntime(781):     at android.support.v4.app.FragmentPagerAdapter.finishUpdate(FragmentPagerAdapter.java:141)
     01-08 15:16:11.726: E/AndroidRuntime(781):     at android.support.v4.view.ViewPager.populate(ViewPager.java:1012)
     01-08 15:16:11.726: E/AndroidRuntime(781):     at android.support.v4.view.ViewPager.populate(ViewPager.java:881)
     01-08 15:16:11.726: E/AndroidRuntime(781):     at android.support.v4.view.ViewPager.onMeasure(ViewPager.java:1366)
     01-08 15:16:11.726: E/AndroidRuntime(781):     at android.view.View.measure(View.java:15172)
     01-08 15:16:11.726: E/AndroidRuntime(781):     at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:4816)
     01-08 15:16:11.726: E/AndroidRuntime(781):     at android.widget.FrameLayout.onMeasure(FrameLayout.java:310)
     01-08 15:16:11.726: E/AndroidRuntime(781):     at android.view.View.measure(View.java:15172)
    01-08 15:16:11.726: E/AndroidRuntime(781):  at android.widget.LinearLayout.measureVertical(LinearLayout.java:833)
    01-08 15:16:11.726: E/AndroidRuntime(781):  at android.widget.LinearLayout.onMeasure(LinearLayout.java:574)
    01-08 15:16:11.726: E/AndroidRuntime(781):  at android.view.View.measure(View.java:15172)
    01-08 15:16:11.726: E/AndroidRuntime(781):  at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:4816)
    01-08 15:16:11.726: E/AndroidRuntime(781):  at android.widget.FrameLayout.onMeasure(FrameLayout.java:310)
    01-08 15:16:11.726: E/AndroidRuntime(781):  at com.android.internal.policy.impl.PhoneWindow$DecorView.onMeasure(PhoneWindow.java:2148)
    01-08 15:16:11.726: E/AndroidRuntime(781):  at android.view.View.measure(View.java:15172)
    01-08 15:16:11.726: E/AndroidRuntime(781):  at android.view.ViewRootImpl.performMeasure(ViewRootImpl.java:1850)
    01-08 15:16:11.726: E/AndroidRuntime(781):  at android.view.ViewRootImpl.measureHierarchy(ViewRootImpl.java:1102)
    01-08 15:16:11.726: E/AndroidRuntime(781):  at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:1275)
    01-08 15:16:11.726: E/AndroidRuntime(781):  at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:1000)
    01-08 15:16:11.726: E/AndroidRuntime(781):  at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:4214)
    01-08 15:16:11.726: E/AndroidRuntime(781):  at android.view.Choreographer$CallbackRecord.run(Choreographer.java:725)
    01-08 15:16:11.726: E/AndroidRuntime(781):  at android.view.Choreographer.doCallbacks(Choreographer.java:555)
    01-08 15:16:11.726: E/AndroidRuntime(781):  at android.view.Choreographer.doFrame(Choreographer.java:525)
    01-08 15:16:11.726: E/AndroidRuntime(781):  at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:711)
    01-08 15:16:11.726: E/AndroidRuntime(781):  at android.os.Handler.handleCallback(Handler.java:615)
    01-08 15:16:11.726: E/AndroidRuntime(781):  at android.os.Handler.dispatchMessage(Handler.java:92)
    01-08 15:16:11.726: E/AndroidRuntime(781):  at android.os.Looper.loop(Looper.java:137)
    01-08 15:16:11.726: E/AndroidRuntime(781):  at android.app.ActivityThread.main(ActivityThread.java:4745)
    01-08 15:16:11.726: E/AndroidRuntime(781):  at java.lang.reflect.Method.invokeNative(Native Method)
    01-08 15:16:11.726: E/AndroidRuntime(781):  at java.lang.reflect.Method.invoke(Method.java:511)
    01-08 15:16:11.726: E/AndroidRuntime(781):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:786)
    01-08 15:16:11.726: E/AndroidRuntime(781): at    com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
    01-08 15:16:11.726: E/AndroidRuntime(781): at dalvik.system.NativeStart.main(Native Method)
    01-08 15:21:11.768: I/Process(781): Sending signal. PID: 781 SIG: 9

我该如何解决这个问题？有任何想法吗？

提前致谢

score 0 · Accepted Answer

你必须初始化你的地图。我在 SherlockFragment 中使用了它，但也许对你有用。

@Override
public void onActivityCreated(Bundle savedInstanceState)
{
    super.onActivityCreated(savedInstanceState);
    mapView.onCreate(savedInstanceState);
    try {
        MapsInitializer.initialize(getActivity());
    } catch (GooglePlayServicesNotAvailableException e) {
        e.printStackTrace();
    }
    GoogleMap map=mapView.getMap();
}

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState)
{
    View myFragmentView = inflater.inflate(R.layout.fragment_mapsearch, container, false);
    mapView = (MapView) myFragmentView.findViewById(R.id.mapSearchView);

    return myFragmentView;
}

score 0 · Accepted Answer

这是我的解决方案：

在MainActivity其中扩展FragmentActivty：

public class MainActivity extends FragmentActivity implements {

private static final int RQS_GooglePlayServices = 0;
SecondFragment sFragment;
Map mapFragment;
SectionsPagerAdapter mySectionsPagerAdapter;
ViewPager myViewPager;
GoogleMap myMap;
String provider;
LocationManager lm;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.main);

    getWindow().addFlags(WindowManager.LayoutParams.FLAG_KEEP_SCREEN_ON);

    setSectionPagerAdapter();       
}

public void setSectionPagerAdapter() {
    mySectionsPagerAdapter = new SectionsPagerAdapter(getSupportFragmentManager());

    myViewPager = (ViewPager) findViewById(R.id.pager);
    myViewPager.setAdapter(mySectionsPagerAdapter);
}

public void initMap() {
    mapFragment = (Map)mySectionsPagerAdapter.getItem(0);
    mapFragment.smf = (SupportMapFragment)getSupportFragmentManager().findFragmentById(R.id.googleMap);

    myMap = mapFragment.smf.getMap();
    myMap.setMapType(GoogleMap.MAP_TYPE_NORMAL);
    myMap.setMyLocationEnabled(true);
    myMap.getUiSettings().setAllGesturesEnabled(false);
    myMap.getUiSettings().setZoomControlsEnabled(false);

    lm = (LocationManager)getSystemService(LOCATION_SERVICE);
    provider = LocationManager.GPS_PROVIDER;

    Location location = lm.getLastKnownLocation(provider);

    if(provider != null ) {
        onLocationChanged(location);
    }
    lm.requestLocationUpdates(provider, 0, 0, this); 
}

...

该类Fragment看起来像：

public class Map extends Fragment {


public SupportMapFragment smf;
MainActivity mainActivity = (MainActivity) getActivity();

public Map(int position) {
}

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

    View v = inflater.inflate(R.layout.fragment_map, container, false);

                mainActivity.initStart();
}


@Override
public void onAttach(Activity activity) {
    super.onAttach(activity);
     try {
            mainActivity = (MainActivity) activity;
        } catch (ClassCastException e) {
            throw new ClassCastException(activity.toString() + "Error!");
        }
}
}

SectionPagerAdapter：_

public class SectionsPagerAdapter extends FragmentPagerAdapter {

private  Map f1;
private  SecondFragment f2;

public SectionsPagerAdapter(FragmentManager fm) {
    super(fm);
}

@Override
public Fragment getItem(int position) {

    if(position == 0) {
        if (f1 == null) {               
            f1 = new Map(position);         
        }           
        return f1;      
    }       
    else {
        if (f2 == null) {               
            f2 = new SecondFragment(position);          
        }           
        return f2;  
    }
}

@Override
public int getCount() {
    // Show 2 total pages.
    return 2;
}

@Override
public CharSequence getPageTitle(int position) {
    switch (position) {
    case 0:
        return "Map";
    case 1:
        return "Second Fragment";
    }
    return null;
}
}

android - 在视图页面片段中显示地图 v2 NullPointerException

2 回答 2

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