java - 在 fragment 中引用 MapView 时出现异常 - OSMdroid

Question

我已经使用 Activity 使用 OSMdroid 编写了一个应用程序，但我现在正在尝试将其移植到 fragment (尽管我是 fragment 的新手)。我收到错误:“java.lang.NullPointerException:尝试在空对象引用上调用虚方法‘void org.osmdroid.views.MapView.setBuiltInZoomControls(boolean)’”

好像MapView还没有初始化，我是不是初始化错地方了(OnCreateView)？根据 Activity 生命周期，OnCreate 在 OnCreateView 之前被调用，因此无法识别它是有道理的，但我对将代码放在哪里感到困惑。

我实现 fragment 的代码:

 //inflating fragment layout
    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {
        // Inflate the layout for this fragment
        View view = inflater.inflate(R.layout.fragment_map, container, false);
        map = (MapView) view.findViewById(R.id.map);
        return view;
    }

    @Override
    public void onCreate(@Nullable Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        context = getActivity();
        Configuration.getInstance().load(context, PreferenceManager.getDefaultSharedPreferences(context));

        setupMap();
    }

//initializing map
    private void setupMap() {
        //adding zoom and touch controls
        map.setBuiltInZoomControls(true);
        map.setMultiTouchControls(true);

        //getting current location using coarse/fine location so we can set centerpoint
        currentLocation = getCurrentLocation();

... code continues ...

错误堆栈跟踪:

 java.lang.NullPointerException: Attempt to invoke virtual method 'void org.osmdroid.views.MapView.setBuiltInZoomControls(boolean)' on a null object reference
                                                                               at skicompanion.skicompanion.MapFragment.setupMap(MapFragment.java:101)
                                                                               at skicompanion.skicompanion.MapFragment.onCreate(MapFragment.java:86)
                                                                               at android.app.Fragment.performCreate(Fragment.java:2214)
                                                                               at android.app.FragmentManagerImpl.moveToState(FragmentManager.java:947)
                                                                               at android.app.FragmentManagerImpl.moveToState(FragmentManager.java:1153)
                                                                               at android.app.BackStackRecord.run(BackStackRecord.java:800)
                                                                               at android.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:1562)
                                                                               at android.app.FragmentManagerImpl$1.run(FragmentManager.java:487)
                                                                               at android.os.Handler.handleCallback(Handler.java:815)
                                                                               at android.os.Handler.dispatchMessage(Handler.java:104)
                                                                               at android.os.Looper.loop(Looper.java:207)
                                                                               at android.app.ActivityThread.main(ActivityThread.java:5765)
                                                                               at java.lang.reflect.Method.invoke(Native Method)
                                                                               at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:789)
                                                                               at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:679)

Answer 1

在您发布的代码中，您似乎不需要在您的案例中重写 onCreate 方法。只需移动此代码:

    context = getActivity();
    Configuration.getInstance().load(context, PreferenceManager.getDefaultSharedPreferences(context));

    setupMap();

在返回调用之前进入 onCreateView 方法，应该没问题。