java - 为什么我的 getter 得到一个空指针

Question

请给我一个线索，为什么我在获取 getlatitude 的值时会得到一个空指针，以及如何修复它？

主要 Activity

  @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
        setSupportActionBar(toolbar);

        p = new Proximity();

        NavigationView navigationView = (NavigationView) findViewById(R.id.nav_view);
        navigationView.setNavigationItemSelectedListener(this);


        initLocationFetching(MainActivity.this); 
}

 @Override
    public void locationFetched(Location mLocal, Location oldLocation, String time, String locationProvider) {
        super.locationFetched(mLocal, oldLocation, time, locationProvider);
        p.setLatitude(mLocal.getLatitude());
        p.setLongitude(mLocal.getLongitude()); 
}

在我获得值(value)的 fragment 上

  Proximity p = new Proximity();

    public MapFragment(Context c, Activity a) { context = c; activity = a;}

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

        if (android.os.Build.VERSION.SDK_INT >= Build.VERSION_CODES.M) {
            checkLocationPermission();
        }
        // Initializing
        MarkerPoints = new ArrayList<>();

        Toast.makeText(context, "Asdasdasdasdas"+p.getLatitude().toString(), Toast.LENGTH_SHORT).show();

接近度

public class Proximity {
    Double latitude;

    public Double getLatitude() {
        return latitude;
    }

    public void setLatitude(Double latitude) {
        this.latitude = latitude;
    }

    public Double getLongitude() {
        return longitude;
    }

    public void setLongitude(Double longitude) {
        this.longitude = longitude;
    }

    Double longitude;
}

java.lang.RuntimeException: Unable to start activity ComponentInfo{com.mark/com.mark.activity.MainActivity}: java.lang.NullPointerException at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2195) at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2245) at android.app.ActivityThread.access$800(ActivityThread.java:135) at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1196) at android.os.Handler.dispatchMessage(Handler.java:102) at android.os.Looper.loop(Looper.java:136) at android.app.ActivityThread.main(ActivityThread.java:5021) at java.lang.reflect.Method.invokeNative(Native Method) at java.lang.reflect.Method.invoke(Method.java:515) at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:827) at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:643) at dalvik.system.NativeStart.main(Native Method) Caused by: java.lang.NullPointerException at com.fragment.MapFragment.onCreateView(MapFragment.java:113) at android.support.v4.app.Fragment.performCreateView(Fragment.java:2239) at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1332) at android.support.v4.app.FragmentManagerImpl.moveFragmentToExpectedState(FragmentManager.java:1574) at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1641) at android.support.v4.app.BackStackRecord.executeOps(BackStackRecord.java:794) at android.support.v4.app.FragmentManagerImpl.executeOps(FragmentManager.java:2415) at android.support.v4.app.FragmentManagerImpl.executeOpsTogether(FragmentManager.java:2200) at android.support.v4.app.FragmentManagerImpl.optimizeAndExecuteOps(FragmentManager.java:2153) at android.support.v4.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:2063) at android.support.v4.app.FragmentController.execPendingActions(FragmentController.java:388) at android.support.v4.app.FragmentActivity.onStart(FragmentActivity.java:554) at android.support.v7.app.AppCompatActivity.onStart(AppCompatActivity.java:177) at com.mark.BaseActivityLocation.onStart(BaseActivityLocation.java:135) at android.app.Instrumentation.callActivityOnStart(Instrumentation.java:1174) at android.app.Activity.performStart(Activity.java:5437) at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2168) at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2245)  at android.app.ActivityThread.access$800(ActivityThread.java:135)  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1196)  at android.os.Handler.dispatchMessage(Handler.java:102)  at android.os.Looper.loop(Looper.java:136)  at android.app.ActivityThread.main(ActivityThread.java:5021)  at java.lang.reflect.Method.invokeNative(Native Method)  at java.lang.reflect.Method.invoke(Method.java:515)

Answer 1

在你的 fragment 中你创建了一个对象 p 接近度 p = new Proximity(); 但是没有设置成员变量latitude(假设是一个对象)。即纬度为空。 根据日志，在 MapFragment.java 中:行号。 113 您正在尝试访问它。我认为这是显示 Toast 的代码，其中 p.getLatitude().toString() 导致 NullPointerException。

您可能必须在添加 fragment 时使用 Fragment.setArguments 将 Proximity 实例传递给 fragment ，或者在您的 fragment 中创建一个方法并从 Activity 中访问它。 由于 Proximity 的代码未发布，因此我假设 lat 和 long 是对象而不是原始数据类型。