Eu estou usando uma barra de ação no modo de navegação no mainActivity. Guias diferentes têm layouts diferentes e, em uma dessas guias, eu insiro um layout que possui um MapFragment dentro dele. Com o seguinte código, o aplicativo funciona bem, o mapFragments funciona bem, as guias funcionam bem. No entanto, assim que eu quiser acessar o mapFragment embutido no myFragment, use getFragmentManager (). FindFragmentById (R.id.map_add), sempre obtendo null.

Eu tentei usar FragmentManager e FragmentTransaction para adicionar myfragment e o MapFragment, mas ainda obter null de findFragmentById (R.id.map_add). Por favor ajude...

A MainActivity foi inicializada assim:

protected void onCreate(Bundle bundle) {
    super.onCreate(bundle);
    setContentView(R.layout.main);

    // ActionBar gets initiated
    ActionBar actionbar = getActionBar();
    // Tell the ActionBar we want to use Tabs.
    actionbar.setNavigationMode(ActionBar.NAVIGATION_MODE_TABS);
    // initiating the tabs and set text to it.
    ActionBar.Tab myTab = actionbar.newTab().setText("hey");

    // create the fragments we want to use for display content
    Fragment myFragment = new myFragment();

    // set the Tab listener. Now we can listen for clicks.
    myTab.setTabListener(new MyTabsListener(myFragment));


    // add the tabs to the actionbar
    actionbar.addTab(myTab);
    map=((MapFragment)getFragmentManager().findFragmentById(R.id.map_add)).getMap();//line 103

}

o layout da MainActivity, main.xml

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:id="@+id/fragment_container"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:paddingBottom="@dimen/activity_vertical_margin"
android:paddingLeft="@dimen/activity_horizontal_margin"
android:paddingRight="@dimen/activity_horizontal_margin"
android:paddingTop="@dimen/activity_vertical_margin"
tools:context=".MainActivity" >
</RelativeLayout>

o código do listlistener:

    class MyTabsListener implements ActionBar.TabListener {
    public Fragment fragment;

    public MyTabsListener(Fragment fragment) {
        this.fragment = fragment;
    }

    @Override
    public void onTabReselected(Tab tab, FragmentTransaction ft) {

    }

    @Override
    public void onTabSelected(Tab tab, FragmentTransaction ft) {
        ft.replace(R.id.fragment_container, fragment);           
    }

    @Override
    public void onTabUnselected(Tab tab, FragmentTransaction ft) {
        ft.remove(fragment);
    }

}

o código do myFragment:

public static class AddAliasFragment extends Fragment {

    private static View view;

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
            Bundle savedInstanceState) {
        if (view != null) {
            ViewGroup parent = (ViewGroup) view.getParent();
            if (parent != null)
                parent.removeView(view);
        }
        try {
            view = inflater.inflate(R.layout.myfragment_layout, container, false);
        } catch (InflateException e) {
            /* map is already there, just return view as it is */
        }
        return view;
    }

    public MapFragment getMapFragment(){
        return (MapFragment)getFragmentManager().findFragmentById(R.id.map_add);
    } 

}

o layout do myFragment: myfragment_layout.xml

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:id="@+id/map_add_layout"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
>
<EditText
    android:id="@+id/search"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:hint="@string/searchhint"
    />

<Button
    android:id="@+id/searchbtn"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_alignBottom="@+id/search"
    android:layout_toRightOf="@id/search"
    android:text="@string/go" />

<fragment 
      android:id="@+id/map_add"
      android:tag="add"
      android:layout_width="match_parent"
      android:layout_height="match_parent"
      android:layout_below="@id/search"
      android:name="com.google.android.gms.maps.MapFragment"/>

a saída do Logcat: a exceção nullpointer se refere à linha 103, que é a linha getMap (), tenho um comentário após ela no código mencionado anteriormente

04-02 21:23:12.122: E/AndroidRuntime(3672): FATAL EXCEPTION: main
04-02 21:23:12.122: E/AndroidRuntime(3672): java.lang.RuntimeException: Unable to start     activity ComponentInfo{com.test.test/com.test.test.MainActivity}:     java.lang.NullPointerException
04-02 21:23:12.122: E/AndroidRuntime(3672):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2307)
04-02 21:23:12.122: E/AndroidRuntime(3672):     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2357)
04-02 21:23:12.122: E/AndroidRuntime(3672):     at android.app.ActivityThread.access$600(ActivityThread.java:153)
04-02 21:23:12.122: E/AndroidRuntime(3672):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1247)
04-02 21:23:12.122: E/AndroidRuntime(3672):     at android.os.Handler.dispatchMessage(Handler.java:99)
04-02 21:23:12.122: E/AndroidRuntime(3672):     at android.os.Looper.loop(Looper.java:137)
04-02 21:23:12.122: E/AndroidRuntime(3672):     at android.app.ActivityThread.main(ActivityThread.java:5226)
04-02 21:23:12.122: E/AndroidRuntime(3672):     at java.lang.reflect.Method.invokeNative(Native Method)
04-02 21:23:12.122: E/AndroidRuntime(3672):     at java.lang.reflect.Method.invoke(Method.java:511)
04-02 21:23:12.122: E/AndroidRuntime(3672):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:795)
04-02 21:23:12.122: E/AndroidRuntime(3672):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:562)
04-02 21:23:12.122: E/AndroidRuntime(3672):     at dalvik.system.NativeStart.main(Native Method)
04-02 21:23:12.122: E/AndroidRuntime(3672): Caused by: java.lang.NullPointerException
04-02 21:23:12.122: E/AndroidRuntime(3672):     at     com.test.test.MainActivity.onCreate(MainActivity.java:103)
04-02 21:23:12.122: E/AndroidRuntime(3672):     at android.app.Activity.performCreate(Activity.java:5104)
04-02 21:23:12.122: E/AndroidRuntime(3672):     at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1080)
04-02 21:23:12.122: E/AndroidRuntime(3672):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2261)
04-02 21:23:12.122: E/AndroidRuntime(3672):     ... 11 more