SupportMapFragment和NullPointerException

Question

我正在尝试使用SupportMapFragment，并得到了以下错误：

java.lang.NullPointerException: Attempt to invoke interface method 'void com.google.maps.api.android.lib6.c.c.o()' on a null object reference
        at com.google.maps.api.android.lib6.c.z.b(Unknown Source)

错误出现在这里的某个地方：

    @Override
public void onViewCreated(View view, Bundle savedInstanceState) {

    SupportMapFragment supportMapFragment;

    if (Build.VERSION.SDK_INT < 21) {
        supportMapFragment = (SupportMapFragment) getActivity().getSupportFragmentManager().findFragmentById(R.id.map);
    } else {
        supportMapFragment = (SupportMapFragment) getChildFragmentManager().findFragmentById(R.id.map);
    }

    supportMapFragment.getMapAsync(this);

    super.onViewCreated(view, savedInstanceState);
}

我实现了OnMapReadyCallBack：

public class MapsFragment extends SupportMapFragment implements OnMapReadyCallback {

我不知道空引用在哪里。

onCreate函数：

    @Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
                         Bundle savedInstanceState) {
   // Inflate the layout for this fragment
    return inflater.inflate(R.layout.fragment_maps, container, false);
}

堆叠轨道：

03-22 22:38:07.291    3758-3758/itcc.li.lieventuregradle E/AndroidRuntime﹕ FATAL EXCEPTION: main
Process: itcc.li.lieventuregradle, PID: 3758
java.lang.NullPointerException: Attempt to invoke interface method 'void com.google.maps.api.android.lib6.c.c.o()' on a null object reference
        at com.google.maps.api.android.lib6.c.z.b(Unknown Source)
        at com.google.android.gms.maps.internal.x.onTransact(SourceFile:115)
        at android.os.Binder.transact(Binder.java:380)
        at com.google.android.gms.maps.internal.IMapFragmentDelegate$a$a.onResume(Unknown Source)
        at com.google.android.gms.maps.SupportMapFragment$a.onResume(Unknown Source)
        at com.google.android.gms.dynamic.a$7.b(Unknown Source)
        at com.google.android.gms.dynamic.a.a(Unknown Source)
        at com.google.android.gms.dynamic.a.onResume(Unknown Source)
        at com.google.android.gms.maps.SupportMapFragment.onResume(Unknown Source)
        at android.support.v4.app.Fragment.performResume(Fragment.java:1829)
        at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:993)
        at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1136)
        at android.support.v4.app.BackStackRecord.run(BackStackRecord.java:739)
        at android.support.v4.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:1499)
        at android.support.v4.app.FragmentManagerImpl$1.run(FragmentManager.java:456)
        at android.os.Handler.handleCallback(Handler.java:739)
        at android.os.Handler.dispatchMessage(Handler.java:95)
        at android.os.Looper.loop(Looper.java:135)
        at android.app.ActivityThread.main(ActivityThread.java:5257)
        at java.lang.reflect.Method.invoke(Native Method)
        at java.lang.reflect.Method.invoke(Method.java:372)
        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:903)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:698)

fragment_maps.xml：

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

​

Answer 1

问题1)

如果代码中确实有下面一行(这是正确的)

public class MapsFragment extends SupportMapFragment ...

然后删除onCreateView方法。

你想把地图碎片放大成地图碎片。

问题2)

摆脱这令人憎恶的东西。

if (Build.VERSION.SDK_INT < 21) {
    supportMapFragment = (SupportMapFragment) getActivity().getSupportFragmentManager().findFragmentById(R.id.map);
} else {
    supportMapFragment = (SupportMapFragment) getChildFragmentManager().findFragmentById(R.id.map);
}

根据需要调用getFragmentManager()或getChildFragmentManager()，从片段中访问片段管理器。这两个实例都是支持片段管理器的实例，因为您正在使用支持片段。

而且你不需要找到地图碎片，你就是它。

问题3)

尊重生命周期逻辑。在重写方法的开头调用super.onViewCreated(...)，在重写方法的末尾调用super.onDestroyView() (如果要使用它)。同样，您希望该片段的祖先先初始化，最后清理。