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我正在尝试做一个使用 ViewPager 的 android 应用程序。在第三页中，我有一个在片段的 xml 中实例化的地图：

<?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"
tools:context=".MainActivity"
android:orientation="vertical">

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

</RelativeLayout>

因此，当我尝试在通过地图的 id 扩展片段的类的onStart()之后获取地图时，我得到一个NullPointerException。

public void onStart() {
    SupportMapFragment mapFragment = (SupportMapFragment) getFragmentManager().findFragmentById(R.id.map);

    mMap = mapFragment.getMap();

    esperandoLoc.setVisibility(View.VISIBLE);

    inicialitzarLoc();

    fragmentMap = this;

    if (mMap== null)
    {
        Toast.makeText(getActivity(),"Google Maps not Available",
                Toast.LENGTH_LONG).show();
    }

}

Debuggin 我发现 FragmentManager 正确地包含了 ViewPager 的五个片段，但其中的地图片段不存在。

知道如何正确获取地图吗？谢谢你。

编辑 我忘了说我在片段类的onCreate()中膨胀了包含地图的片段：

public View onCreateView(LayoutInflater inflater, ViewGroup container,Bundle savedInstanceState) {
View v = inflater.inflate(R.layout.fragment_mapa, container, false);

我运行后得到的logcat错误是下一个：

05-18 20:41:29.725: E/AndroidRuntime(20636): FATAL EXCEPTION: main
05-18 20:41:29.725: E/AndroidRuntime(20636): Process: com.example.app, PID: 20636
05-18 20:41:29.725: E/AndroidRuntime(20636): java.lang.NullPointerException
05-18 20:41:29.725: E/AndroidRuntime(20636):    at fragments.MapaTab.inicialitzarMapa(MapaTab.java:113)
05-18 20:41:29.725: E/AndroidRuntime(20636):    at fragments.MapaTab.inicialitzarLoc(MapaTab.java:108)
05-18 20:41:29.725: E/AndroidRuntime(20636):    at fragments.MapaTab.onActivityCreated(MapaTab.java:90)
05-18 20:41:29.725: E/AndroidRuntime(20636):    at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:892)
05-18 20:41:29.725: E/AndroidRuntime(20636):    at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1083)
05-18 20:41:29.725: E/AndroidRuntime(20636):    at android.support.v4.app.BackStackRecord.run(BackStackRecord.java:635)
05-18 20:41:29.725: E/AndroidRuntime(20636):    at android.support.v4.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:1431)
05-18 20:41:29.725: E/AndroidRuntime(20636):    at android.support.v4.app.FragmentManagerImpl.executePendingTransactions(FragmentManager.java:431)
05-18 20:41:29.725: E/AndroidRuntime(20636):    at android.support.v4.app.FragmentPagerAdapter.finishUpdate(FragmentPagerAdapter.java:141)
05-18 20:41:29.725: E/AndroidRuntime(20636):    at android.support.v4.view.ViewPager.populate(ViewPager.java:895)
05-18 20:41:29.725: E/AndroidRuntime(20636):    at android.support.v4.view.ViewPager.setCurrentItemInternal(ViewPager.java:469)
05-18 20:41:29.725: E/AndroidRuntime(20636):    at android.support.v4.view.ViewPager.setCurrentItemInternal(ViewPager.java:441)
05-18 20:41:29.725: E/AndroidRuntime(20636):    at android.support.v4.view.ViewPager.setCurrentItem(ViewPager.java:422)
05-18 20:41:29.725: E/AndroidRuntime(20636):    at com.example.app.MainActivity.onTabSelected(MainActivity.java:136)
05-18 20:41:29.725: E/AndroidRuntime(20636):    at com.android.internal.app.ActionBarImpl.selectTab(ActionBarImpl.java:577)
05-18 20:41:29.725: E/AndroidRuntime(20636):    at com.android.internal.app.ActionBarImpl$TabImpl.select(ActionBarImpl.java:1105)
05-18 20:41:29.725: E/AndroidRuntime(20636):    at com.android.internal.widget.ScrollingTabContainerView$TabClickListener.onClick(ScrollingTabContainerView.java:547)
05-18 20:41:29.725: E/AndroidRuntime(20636):    at android.view.View.performClick(View.java:4438)
05-18 20:41:29.725: E/AndroidRuntime(20636):    at android.view.View$PerformClick.run(View.java:18422)
05-18 20:41:29.725: E/AndroidRuntime(20636):    at android.os.Handler.handleCallback(Handler.java:733)
05-18 20:41:29.725: E/AndroidRuntime(20636):    at android.os.Handler.dispatchMessage(Handler.java:95)
05-18 20:41:29.725: E/AndroidRuntime(20636):    at android.os.Looper.loop(Looper.java:136)
05-18 20:41:29.725: E/AndroidRuntime(20636):    at android.app.ActivityThread.main(ActivityThread.java:5017)
05-18 20:41:29.725: E/AndroidRuntime(20636):    at java.lang.reflect.Method.invokeNative(Native Method)
05-18 20:41:29.725: E/AndroidRuntime(20636):    at java.lang.reflect.Method.invoke(Method.java:515)
05-18 20:41:29.725: E/AndroidRuntime(20636):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:779)
05-18 20:41:29.725: E/AndroidRuntime(20636):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:595)
05-18 20:41:29.725: E/AndroidRuntime(20636):    at dalvik.system.NativeStart.main(Native Method)
4

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