java - NullPointerException - 使用 fragment 中的位置

Question

我在尝试运行应用程序时意外收到以下 NullPointer Exception 错误。

09-22 20:22:49.981: E/AndroidRuntime(4751): FATAL EXCEPTION: main
    09-22 20:22:49.981: E/AndroidRuntime(4751): Process: com.dooba.beta, PID: 4751
    09-22 20:22:49.981: E/AndroidRuntime(4751): java.lang.NullPointerException
    09-22 20:22:49.981: E/AndroidRuntime(4751):     at com.dooba.beta.Fragment1.setConversationsList(Fragment1.java:154)
    09-22 20:22:49.981: E/AndroidRuntime(4751):     at com.dooba.beta.Fragment1.onActivityCreated(Fragment1.java:97)
    09-22 20:22:49.981: E/AndroidRuntime(4751):     at android.support.v4.app.Fragment.performActivityCreated(Fragment.java:1468)
    09-22 20:22:49.981: E/AndroidRuntime(4751):     at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:931)
    09-22 20:22:49.981: E/AndroidRuntime(4751):     at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1088)
    09-22 20:22:49.981: E/AndroidRuntime(4751):     at android.support.v4.app.BackStackRecord.run(BackStackRecord.java:682)
    09-22 20:22:49.981: E/AndroidRuntime(4751):     at android.support.v4.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:1444)
    09-22 20:22:49.981: E/AndroidRuntime(4751):     at android.support.v4.app.FragmentManagerImpl.executePendingTransactions(FragmentManager.java:461)
    09-22 20:22:49.981: E/AndroidRuntime(4751):     at android.support.v4.app.FragmentPagerAdapter.finishUpdate(FragmentPagerAdapter.java:141)
    09-22 20:22:49.981: E/AndroidRuntime(4751):     at android.support.v4.view.ViewPager.populate(ViewPager.java:1011)
    09-22 20:22:49.981: E/AndroidRuntime(4751):     at android.support.v4.view.ViewPager.populate(ViewPager.java:880)
    09-22 20:22:49.981: E/AndroidRuntime(4751):     at android.support.v4.view.ViewPager.onMeasure(ViewPager.java:1374)
    09-22 20:22:49.981: E/AndroidRuntime(4751):     at android.view.View.measure(View.java:16497)
    09-22 20:22:49.981: E/AndroidRuntime(4751):     at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5125)
    09-22 20:22:49.981: E/AndroidRuntime(4751):     at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1404)
    09-22 20:22:49.981: E/AndroidRuntime(4751):     at android.widget.LinearLayout.measureVertical(LinearLayout.java:695)
    09-22 20:22:49.981: E/AndroidRuntime(4751):     at android.widget.LinearLayout.onMeasure(LinearLayout.java:588)
    09-22 20:22:49.981: E/AndroidRuntime(4751):     at android.view.View.measure(View.java:16497)
    09-22 20:22:49.981: E/AndroidRuntime(4751):     at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5125)
    09-22 20:22:49.981: E/AndroidRuntime(4751):     at android.widget.FrameLayout.onMeasure(FrameLayout.java:310)
    09-22 20:22:49.981: E/AndroidRuntime(4751):     at android.view.View.measure(View.java:16497)
    09-22 20:22:49.981: E/AndroidRuntime(4751):     at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5125)
    09-22 20:22:49.981: E/AndroidRuntime(4751):     at com.android.internal.widget.ActionBarOverlayLayout.onMeasure(ActionBarOverlayLayout.java:327)
    09-22 20:22:49.981: E/AndroidRuntime(4751):     at android.view.View.measure(View.java:16497)
    09-22 20:22:49.981: E/AndroidRuntime(4751):     at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5125)
    09-22 20:22:49.981: E/AndroidRuntime(4751):     at android.widget.FrameLayout.onMeasure(FrameLayout.java:310)
    09-22 20:22:49.981: E/AndroidRuntime(4751):     at com.android.internal.policy.impl.PhoneWindow$DecorView.onMeasure(PhoneWindow.java:2291)
    09-22 20:22:49.981: E/AndroidRuntime(4751):     at android.view.View.measure(View.java:16497)
    09-22 20:22:49.981: E/AndroidRuntime(4751):     at android.view.ViewRootImpl.performMeasure(ViewRootImpl.java:1916)
    09-22 20:22:49.981: E/AndroidRuntime(4751):     at android.view.ViewRootImpl.measureHierarchy(ViewRootImpl.java:1113)
    09-22 20:22:49.981: E/AndroidRuntime(4751):     at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:1295)
    09-22 20:22:49.981: E/AndroidRuntime(4751):     at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:1000)
    09-22 20:22:49.981: E/AndroidRuntime(4751):     at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:5670)
    09-22 20:22:49.981: E/AndroidRuntime(4751):     at android.view.Choreographer$CallbackRecord.run(Choreographer.java:761)
    09-22 20:22:49.981: E/AndroidRuntime(4751):     at android.view.Choreographer.doCallbacks(Choreographer.java:574)
    09-22 20:22:49.981: E/AndroidRuntime(4751):     at android.view.Choreographer.doFrame(Choreographer.java:544)
    09-22 20:22:49.981: E/AndroidRuntime(4751):     at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:747)
    09-22 20:22:49.981: E/AndroidRuntime(4751):     at android.os.Handler.handleCallback(Handler.java:733)
    09-22 20:22:49.981: E/AndroidRuntime(4751):     at android.os.Handler.dispatchMessage(Handler.java:95)
    09-22 20:22:49.981: E/AndroidRuntime(4751):     at android.os.Looper.loop(Looper.java:136)
    09-22 20:22:49.981: E/AndroidRuntime(4751):     at android.app.ActivityThread.main(ActivityThread.java:5017)
    09-22 20:22:49.981: E/AndroidRuntime(4751):     at java.lang.reflect.Method.invokeNative(Native Method)
    09-22 20:22:49.981: E/AndroidRuntime(4751):     at java.lang.reflect.Method.invoke(Method.java:515)
    09-22 20:22:49.981: E/AndroidRuntime(4751):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:779)
    09-22 20:22:49.981: E/AndroidRuntime(4751):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:595)
    09-22 20:22:49.981: E/AndroidRuntime(4751):     at dalvik.system.NativeStart.main(Native Method)

下面是第 154 行所指示的内容，我假设第 155 行也会出现类似的问题。

    Location ln;
    Location lt;
    double longi=lt.getLongitude();
    double lati=ln.getLatitude();

    ParseGeoPoint point = new ParseGeoPoint(lati, longi); 
    query.whereWithinKilometers("location", point, 100);

本质上，我正在尝试根据各种条件检索用户，在本例中，它是导致问题的位置。

任何帮助将不胜感激。提前致谢。

更新:

   Location location = new Location(""); // location
                    double lati; // latitude
                    double longi; // longitude
                    lati = location.getLatitude();
                    longi = location.getLongitude();


                    ParseGeoPoint point = new ParseGeoPoint(lati, longi); 
                    query.whereWithinKilometers("location", point, 100);

更新2:

我已经成功地使用以下方法获取用户纬度和经度:

@Override
        public void onLocationChanged(Location userLocation) {
            // TODO Auto-generated method stub
            double lati = userLocation.getLatitude();
            double longi = userLocation.getLongitude();

            }

问题是将其合并到当前 fragment 代码中是有问题的。

private void setConversationsList() {
        currentUserId = ParseUser.getCurrentUser().getObjectId();


        // String userActivitySelectionName = null;

        ParseQuery<ParseUser> query = ParseUser.getQuery();

        // query.whereEqualTo("ActivityName",userActivitySelectionName);

        query.whereNotEqualTo("objectId", ParseUser.getCurrentUser()
                .getObjectId());

        query.setLimit(1);


        Location location = new Location(""); // location
        double lati; // latitude
        double longi; // longitude
        lati = location.getLatitude();
        longi = location.getLongitude();


        ParseGeoPoint point = new ParseGeoPoint(57, -122); 
        query.whereWithinKilometers("location", point, 1113);


        query.orderByDescending("Name");

        ParseQuery<ParseUser> query1 = ParseUser.getQuery();

Answer 1

在按下 ctrl-f'ing 代码后，我没有找到 lt 的任何赋值('lt='、'lt' 或 '(lt)')。您可能应该在使用变量之前对其进行初始化。另外，您应该删除不相关的代码部分，这样人们就不必阅读大约 200-300 行与您的问题无关的代码。

您似乎缺乏字段/变量初始化的基本知识，但无论如何，我最近做了类似的事情，您可以在这里查看代码:https://github.com/dbarwacz/Beton