Question

我正在尝试开发依赖于网络服务的Android应用程序，并且我使用片段让我的应用程序在移动设备和平板电脑上运行..

这是在两种模式下保存片段并检查哪种模式的活动然后根据哪种模式定义onItemClickListener，详细信息显示在DetailFragment（Landscape）或DetailActivity（Portrait）

public class AppelsFragment extends Fragment implements AdapterView.OnItemClickListener {
    boolean mDualPane;
    int mCurCheckPosition = 0;

    public static List<Appel> appels = null;
    ListView mListView;

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
        View view = inflater.inflate(R.layout.list_fragment, container, false);

        return view;
    }

    @Override
    public void onActivityCreated(Bundle savedInstanceState) {
        super.onActivityCreated(savedInstanceState);

        mListView = (ListView) getActivity().findViewById(R.id.listAppels);

        if (this.mListView != null) {
            this.mListView.setOnItemClickListener(this);
            this.mListView.setChoiceMode(ListView.CHOICE_MODE_SINGLE);
        }

        // this is an asynctask that retreive data from RestAPI and set the Adapter for my listview
        new Appels().execute();


        View detailsFrame = getActivity().findViewById(R.id.details);


        mDualPane = detailsFrame != null
                && detailsFrame.getVisibility() == View.VISIBLE;


        if (savedInstanceState != null) {
            // Restore last state for checked position.
            mCurCheckPosition = savedInstanceState.getInt("curChoice", 0);
        }

        if (mDualPane) {

            showDetails(mCurCheckPosition);
        } else {
            mListView.setItemChecked(mCurCheckPosition, true);
        }
    }

    @Override
    public void onSaveInstanceState(Bundle outState) {
        super.onSaveInstanceState(outState);

        outState.putInt("curChoice", mCurCheckPosition);
    }

    @Override
    public void onItemClick(AdapterView<?> l, View v, int position, long id) {

        showDetails(position);
    }


    void showDetails(int index) {
        mCurCheckPosition = index;

        if (mDualPane) {

            mListView.setItemChecked(index, true);

            DetailsFragment details = (DetailsFragment) getFragmentManager()
                    .findFragmentById(R.id.details);
            if (details == null || details.getShownIndex() != index) {

                details = DetailsFragment.newInstance(index);

                FragmentTransaction ft = getFragmentManager()
                        .beginTransaction();
                ft.replace(R.id.details, details);
                ft.setTransition(FragmentTransaction.TRANSIT_FRAGMENT_FADE);
                ft.commit();
            }

        } else {

            Intent intent = new Intent();

            intent.setClass(getActivity(), DetailsActivity.class);

            intent.putExtra("index", index);

            startActivity(intent);
        }
    }

class Appels extends AsyncTask<String, Void, List<Appel>> {
..... }
}

我面临的问题是DetailFragment中的NullPointerException，在Portrait模式下我没有问题

java.lang.RuntimeException: Unable to start activity ComponentInfo{com.mycompany.marocbusiness11.app/com.mycompany.marocbusiness11.app.FragmentLayout}: 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:5017)
            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:779)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:595)
            at dalvik.system.NativeStart.main(Native Method)
     Caused by: java.lang.NullPointerException
            at com.mycompany.marocbusiness11.app.DetailsFragment.onCreateView(DetailsFragment.java:42)
            at android.app.Fragment.performCreateView(Fragment.java:1700)
            at android.app.FragmentManagerImpl.moveToState(FragmentManager.java:890)
            at android.app.FragmentManagerImpl.moveToState(FragmentManager.java:1062)
            at android.app.BackStackRecord.run(BackStackRecord.java:684)
            at android.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:1447)
            at android.app.Activity.performStart(Activity.java:5240)
            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:5017)
            at java.lang.reflect.Method.invokeNative(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:515)

这是DetailFragment的代码

public class DetailsFragment extends Fragment {

    public static DetailsFragment newInstance(int index) {
        DetailsFragment f = new DetailsFragment();

        // Supply index input as an argument.
        Bundle args = new Bundle();
        args.putInt("index", index);
        f.setArguments(args);

        return f;
    }

    public int getShownIndex() {
        return getArguments().getInt("index", 0);
    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {

        if(container == null)
            return null;

        View v = inflater.inflate(R.layout.details,container,false);
        TextView txtAffichage = (TextView) v.findViewById(R.id.txtAffichage);
        txtAffichage.setText(AppelsFragment.appels.get(getShownIndex()).getNumOrdre().toString());

        return v;

    }
}

此指令触发的问题

txtAffichage.setText(AppelsFragment.appels.get(getShownIndex()).getNumOrdre().toString());

我认为我定义列表的方式是

public static List<Appel> appels = null;

可能是导致此问题的原因，如果有任何关于我如何处理它的建议或者我应该改变什么

提前致谢

///////发布后编辑

在纵向模式中我使用DetailsActivity来实例化DetailsFragment，所以它总是关于Fragment ..

这是DetailsActivity的代码

public class DetailsActivity extends Activity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        if (getResources().getConfiguration().orientation == Configuration.ORIENTATION_LANDSCAPE) {

            finish();
            return;
        }

        if (savedInstanceState == null) {

            DetailsFragment details = new DetailsFragment();

            details.setArguments(getIntent().getExtras());

            getFragmentManager().beginTransaction()
                    .add(android.R.id.content, details).commit();
        }
    }
}

和details.xml布局

<?xml version="1.0" encoding="utf-8"?>

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical" android:layout_width="match_parent"
    android:layout_height="match_parent">

        <TextView
            android:id="@+id/txtAffichage"
            android:layout_width="match_parent"
            android:layout_height="match_parent" />

</LinearLayout>

Answer 1

这一行：

TextView txtAffichage = (TextView) v.findViewById(R.id.txtAffichage);

可能正在返回null。确保R.id.txtAffichage在布局资源文件的两个版本（纵向和横向）中都有效。

Answer 2

我已经编辑了我的帖子以添加一些代码，但经过一些研究（here和here）并纠正我，如果我错了..我的asyncTask中的问题与片段有关，asnycTask负责从我的Rest API中获取数据作为List，列出我试图在我的片段中显示和使用的数据，由于连接和网络质量而导致的asyncTask无法在数据之前检索数据。片段尝试显示它们..

触发此指令时

TextView txtAffichage = (TextView) v.findViewById(R.id.txtAffichage);
        txtAffichage.setText(AppelsFragment.appels.get(getShownIndex()).getNumOrdre().toString());

List appels仍为空，并从那里出现NullPointerException异常..

我认为装载机是解决这个问题的方法，如果不是，请纠正我。

java.lang.NullPointerException当我尝试在android中的片段之间获取数据时

2 个答案: