我的片段状态寻呼机适配器中的空指针异常

Question

我正在尝试在其中使用 Fragment Activity 我有带有片段状态适配器的 View 寻呼机。它运行良好，但例如，如果发生错误并且它必须返回到此片段，它会在 theragmentStatePagerAdapter 中给出 NullPointerException。

我看到一些类似的问题说可能是 getItem() 方法或使用了错误的库。但是我检查了，这不是问题。

import android.os.AsyncTask;
import android.os.Looper;
import android.os.Parcelable;
import android.support.annotation.Nullable;
import android.support.design.widget.FloatingActionButton;
import android.support.design.widget.Snackbar;
import android.support.design.widget.TabLayout;
import android.support.v4.app.FragmentManager;
import android.support.v4.app.FragmentPagerAdapter;
import android.support.v4.app.FragmentStatePagerAdapter;
import android.support.v4.view.ViewPager;
import android.support.v4.widget.DrawerLayout;
import android.support.v4.widget.SwipeRefreshLayout;
import android.support.v7.app.AppCompatActivity;
import android.support.v7.widget.GridLayoutManager;
import android.support.v7.widget.LinearLayoutManager;
import android.support.v7.widget.RecyclerView;
import android.support.v7.widget.Toolbar;

import android.support.v4.app.Fragment;
import android.os.Bundle;
import android.util.Log;
import android.view.LayoutInflater;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.view.ViewGroup;
import android.widget.AdapterView;
import android.widget.AdapterView.OnItemSelectedListener;
import android.widget.ArrayAdapter;
import android.widget.Spinner;
import android.content.Context;
import android.support.v7.widget.ThemedSpinnerAdapter;
import android.content.res.Resources.Theme;

import android.widget.TextView;
import android.widget.Toast;

import org.jsoup.Jsoup;
import org.jsoup.nodes.Document;
import org.jsoup.nodes.Element;
import org.jsoup.select.Elements;

import java.io.IOException;
import java.util.ArrayList;

public class HomeFragment extends Fragment {


static Context c;
static LatestChapterAdapter adapter;
static PopularAdapter adapter2;
static ArrayList<LatestChapter> list;
static ArrayList<PopularManga> list2;

static SwipeRefreshLayout swipe;
static SwipeRefreshLayout swipe2;
static TextView error;
static TextView error2;

public static int Page;

static boolean Arabic;


/**
 * The {@link android.support.v4.view.PagerAdapter} that will provide
 * fragments for each of the sections. We use a
 * {@link FragmentPagerAdapter} derivative, which will keep every
 * loaded fragment in memory. If this becomes too memory intensive, it
 * may be best to switch to a
 * {@link android.support.v4.app.FragmentStatePagerAdapter}.
 */
private SectionsPagerAdapter mSectionsPagerAdapter;

/**
 * The {@link ViewPager} that will host the section contents.
 */

private ViewPager mViewPager;

FragmentManager manager;

public HomeFragment(){}

public HomeFragment(Context context,FragmentManager fragmentManager){
    c = context;
    manager = fragmentManager;
}

@Override
public void onCreate(@Nullable Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
}

@Override
public void onActivityCreated(@Nullable Bundle savedInstanceState) {
    super.onActivityCreated(savedInstanceState);
    Arabic = Constants.getLanguage(c).equals("arabic");

}

@Nullable
@Override
public View onCreateView(LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
    View v = inflater.inflate(R.layout.fragment_main2,container,false);

    mSectionsPagerAdapter = new SectionsPagerAdapter(manager);

    // Set up the ViewPager with the sections adapter.
    mViewPager = (ViewPager)v.findViewById(R.id.container_home);
    mViewPager.setAdapter(mSectionsPagerAdapter);

    TabLayout tabLayout = (TabLayout)v.findViewById(R.id.tabs_main);
    tabLayout.setupWithViewPager(mViewPager);
    return v;
}

@Override
public void onResume() {
    super.onResume();
}

public static class loadLatestChapters extends AsyncTask {

    @Override
    protected void onPreExecute() {
        if (!swipe.isRefreshing()){
            swipe.setRefreshing(true);
        }
        super.onPreExecute();
    }

    @Override
    protected void onPostExecute(Object o) {
        if (swipe.isRefreshing()){
            swipe.setRefreshing(false);
        }
        adapter.notifyDataSetChanged();
        if (list.size() == 0){
            error.setText("connection error\n\b\b  try again");
        }else {
            error.setText("");
        }
        super.onPostExecute(o);
    }

    @Override
    protected Object doInBackground(Object[] params) {
        try {
            if (Looper.myLooper() == null) {
                Looper.prepare();
            }
            Document doc;
            if (Arabic) {

                if (Page == 1) {
                    doc = Jsoup.connect(Constants.MANGA_LATEST_CHAPTERS).timeout(Constants.TIMEOUT).get();
                } else {
                    doc = Jsoup.connect(Constants.MANGA_LATEST_CHAPTERS + "?page=" + String.valueOf(Page))
                            .timeout(Constants.TIMEOUT).get();
                }
                Elements elements = doc.getElementsByClass("manga-item");

                for (int i = 0; i < elements.size(); i++) {
                    Element man = elements.get(i);
                    String manga_url = man.select("h3").select("a").attr("abs:href");
                    String manga_name = man.select("h3").select("a").text();

                    //Document doc2 = Jsoup.connect(manga_url).get();

                    //String picture = doc2.getElementsByClass("boxed").select("img").first().absUrl("src");
                    String picture = Constants.MANGA_COVER_1 + manga_url.
                            replace(Constants.MANGA_COVER_3, "")
                            + Constants.MANGA_COVER_2;

                    Elements elements2 = man.getElementsByClass("manga-chapter");
                    //String ch1 = elements2.first().select("a").text();
                    String ch1_url = elements2.first().select("a").attr("abs:href");
                    double num;
                    try {
                        num = Double.parseDouble(ch1_url.replace(manga_url + "/", ""));
                    } catch (NumberFormatException n) {
                        num = 999999;
                    }
                    String ch1 = String.valueOf((int) num);
                    String ch2;
                    if (num > 1) {
                        ch2 = String.valueOf((int) (num - 1));
                    } else {
                        ch2 = String.valueOf(999999);
                    }
                    String ch2_url = manga_url + "/" + String.valueOf((int) (num - 1));


                    LatestChapter chapter = new LatestChapter(manga_name, manga_url, picture, ch1,
                            ch1_url, ch2, ch2_url);

                    list.add(chapter);

                }
            }else {


                if (Page == 1) {
                    doc = Jsoup.connect(Constants.MANGA_NELO).timeout(Constants.TIMEOUT).get();
                } else {
                    doc = Jsoup.connect(Constants.MANGA_NELO_LATES_NEXT + String.valueOf(Page))
                            .timeout(Constants.TIMEOUT).get();
                }
                Elements elements = doc.getElementsByClass("first");

                for (int i = 0; i < elements.size(); i++) {
                    Element man = elements.get(i);
                    Elements man2 = man.getElementsByTag("ul").get(0).getElementsByTag("li");

                    String manga_url = man.select("h3").select("a").attr("abs:href");
                    String manga_name = man.select("h3").select("a").text();
                    String picture = man.select("a").select("img").first().absUrl("src");

                    String id_manga = manga_url.replace("https://manganelo.com/manga/","");

                    String ch1_url ;
                    String ch1;
                    try {
                        ch1_url = man2.get(1).select("span").select("a").attr("abs:href");
                        ch1 = ch1_url.replace("https://manganelo.com/chapter/" + id_manga + "/chapter_", "");
                    }catch (Exception e){
                        ch1 = String.valueOf(999999);
                        ch1_url = "dsadasdas";
                    }
                    String ch2_url;
                    String ch2;
                    if (man2.size()>2){
                        ch2_url = man2.get(2).select("span").select("a").attr("abs:href");
                        ch2 = ch2_url.replace("https://manganelo.com/chapter/"+id_manga+"/chapter_","");
                    }else {
                        ch2_url = "";
                        ch2 = String.valueOf(999999);
                    }



                    LatestChapter chapter = new LatestChapter(manga_name, manga_url,
                            picture, ch1, ch1_url, ch2, ch2_url);

                    list.add(chapter);

                }


            }


        } catch (IOException e) {
            Toast.makeText(c,"ioe " + e.getMessage(),Toast.LENGTH_LONG).show();
            Log.e("ZZZZZZZZZZZZZZZZZZZZZZZ","  " + e.getMessage());
        } catch (NumberFormatException n){
            Toast.makeText(c,"run " + n.getMessage(),Toast.LENGTH_LONG).show();
            Log.e("CCCCCCCCCCCCCCCCCCCCCCC","  " + n.getMessage());
        } catch (RuntimeException r){
            Toast.makeText(c,"run " + r.getMessage(),Toast.LENGTH_LONG).show();
            Log.e("XXXXXXXXXXXXXXXXXXXXXXX","  " + r.getMessage());
        }
        return null;
    }
}




public static class loadPopular extends AsyncTask{

    @Override
    protected void onPreExecute() {
        if (!swipe2.isRefreshing()){
            swipe2.setRefreshing(true);
        }
        super.onPreExecute();
    }

    @Override
    protected void onPostExecute(Object o) {
        if (swipe2.isRefreshing()){
            swipe2.setRefreshing(false);
        }
        adapter2.notifyDataSetChanged();
        if (list2.size() == 0){
            error2.setText("connection error\n\btry again");
        }else {
            error2.setText("");
        }
        super.onPostExecute(o);
    }

    @Override
    protected Object doInBackground(Object[] params) {
        try {
            if (Looper.myLooper() == null) {
                Looper.prepare();
            }

            if (Arabic) {
                Document doc = Jsoup.connect(Constants.MANGA).timeout(Constants.TIMEOUT).get();

                Elements elements = doc.getElementsByClass("media");

                for (int i = 0; i < elements.size(); i++) {
                    String url = elements.get(i).getElementsByClass("media-left")
                            .select("a").attr("abs:href");
                    String name = elements.get(i).getElementsByClass("media-body")
                            .select("h5").text();
                    String picture = Constants.MANGA_COVER_1 + url.
                            replace(Constants.MANGA_COVER_3, "")
                            + Constants.MANGA_COVER_2;

                    list2.add(new PopularManga(url, picture, name));

                }

            }else {

                Document doc = Jsoup.connect(Constants.MANGA_NELO_TOP_VIEWS)
                        .timeout(Constants.TIMEOUT).get();

                Elements elements = doc.getElementsByClass("list-truyen-item-wrap");

                for (int i = 0; i < elements.size(); i++) {
                    String url = elements.get(i).getElementsByTag("a").get(0).
                            attr("abs:href");
                    String name = elements.get(i).getElementsByTag("h3").get(0).
                            select("a").text();
                    String picture = elements.get(i).getElementsByTag("a").get(0)
                            .select("img").first().absUrl("src");

                    list2.add(new PopularManga(url, picture, name));

                }

            }


        }catch(IOException e){
            Toast.makeText(c, "ioe " + e.getMessage(), Toast.LENGTH_LONG).show();
            Log.e("ZZZZZZZZZZZZZZZZZZZZZZZ", "  " + e.getMessage());
        }catch(NumberFormatException n){
            Toast.makeText(c, "run " + n.getMessage(), Toast.LENGTH_LONG).show();
            Log.e("CCCCCCCCCCCCCCCCCCCCCCC", "  " + n.getMessage());
        }catch(RuntimeException r){
            Toast.makeText(c, "run " + r.getMessage(), Toast.LENGTH_LONG).show();
            Log.e("XXXXXXXXXXXXXXXXXXXXXXX", "  " + r.getMessage());
        }
        return null;
    }
}


public static class PlaceholderFragment extends Fragment {
    /**
     * The fragment argument representing the section number for this
     * fragment.
     */
    private static final String ARG_SECTION_NUMBER = "section_number";

    public PlaceholderFragment() {
    }

    /**
     * Returns a new instance of this fragment for the given section
     * number.
     */
    public static PlaceholderFragment newInstance(int sectionNumber) {
        PlaceholderFragment fragment = new PlaceholderFragment();
        Bundle args = new Bundle();
        args.putInt(ARG_SECTION_NUMBER, sectionNumber);
        fragment.setArguments(args);
        return fragment;
    }

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

        int index = getArguments().getInt(ARG_SECTION_NUMBER);
        if (index == 1) {

            View rootView = inflater.inflate(R.layout.content_main, container, false);

            swipe2 = (SwipeRefreshLayout)rootView.findViewById(R.id.swipe);
            error2 = (TextView)rootView.findViewById(R.id.error);

            swipe2.setRefreshing(true);


            RecyclerView recyclerView = (RecyclerView)rootView. findViewById(R.id.recycler_manga);
            recyclerView.setHasFixedSize(false);
            recyclerView.setNestedScrollingEnabled(false);
            list2 = new ArrayList<>();
            adapter2 = new PopularAdapter(list2, c);

            GridLayoutManager layoutManager = new GridLayoutManager(c,3);
            recyclerView.setLayoutManager(layoutManager);

            recyclerView.setAdapter(adapter2);

            swipe2.setOnRefreshListener(new SwipeRefreshLayout.OnRefreshListener() {
                @Override
                public void onRefresh() {
                    error2.setText("");
                    list2.clear();
                    adapter2.notifyDataSetChanged();
                    new loadPopular().execute();
                }
            });
            new loadPopular().execute();
            return rootView;
        }else if(index == 0 ) {
            View rootView = inflater.inflate(R.layout.content_main, container, false);

            swipe = (SwipeRefreshLayout)rootView.findViewById(R.id.swipe);
            error = (TextView)rootView.findViewById(R.id.error);

            Page = 1;
            swipe.setRefreshing(true);


            RecyclerView recyclerView = (RecyclerView)rootView. findViewById(R.id.recycler_manga);
            recyclerView.setHasFixedSize(false);
            recyclerView.setNestedScrollingEnabled(false);
            list = new ArrayList<>();
            adapter = new LatestChapterAdapter(list, c);

            LinearLayoutManager layoutManager = new LinearLayoutManager(c);
            recyclerView.setLayoutManager(layoutManager);

            recyclerView.setAdapter(adapter);

            swipe.setOnRefreshListener(new SwipeRefreshLayout.OnRefreshListener() {
                @Override
                public void onRefresh() {
                    error.setText("");
                    list.clear();
                    adapter.notifyDataSetChanged();
                    new loadLatestChapters().execute();
                }
            });
            new loadLatestChapters().execute();
            return rootView;
        }
        return null;
    }

    /*@Override
    public void onResume() {
        super.onResume();
        list = new ArrayList<>();
        list2 = new ArrayList<>();
        adapter.notifyDataSetChanged();
        adapter2.notifyDataSetChanged();
        swipe.setRefreshing(true);
        swipe2.setRefreshing(true);
        new loadLatestChapters().execute();
        new loadPopular().execute();
    }*/
}

/**
 * A {@link FragmentPagerAdapter} that returns a fragment corresponding to
 * one of the sections/tabs/pages.
 */
public class SectionsPagerAdapter extends FragmentStatePagerAdapter  {



    public SectionsPagerAdapter(FragmentManager fm) {
        super(fm);
    }

    @Override
    public Fragment getItem(int position) {
        // getItem is called to instantiate the fragment for the given page.
        // Return a PlaceholderFragment (defined as a static inner class below).
        Log.e("POPOPOPOPOPOPOPOPOPOP","po:" + position);
        if (position == 0 || position == 1)
            return PlaceholderFragment.newInstance(position);
        else
            return PlaceholderFragment.newInstance(0);
    }

    @Override
    public int getCount() {
        // Show 3 total pages.
        return 2;
    }

    @Override
    public CharSequence getPageTitle(int position) {
        switch (position) {
            case 0:
                return getResources().getString(R.string.latest);
            case 1:
                return getResources().getString(R.string.popular);
        }
        return null;
    }


    @Override
    public void restoreState(Parcelable state, ClassLoader loader) {
        try {
            super.restoreState(state,loader);
        }catch (NullPointerException n){

        }
    }

}
}

Answer 1

您的 viewPager 正在管理已经在片段内的片段。因此，您需要在 PagerAdapter 中传递 childFragmentManager 而不是 fragmentManager。这可能是异常的原因。

getChildFragmentManager() 的定义是：

Return a private FragmentManager for placing and managing Fragments inside of this Fragment.

我的片段状态寻呼机适配器中的空指针异常

Null Pointer Exception in my Fragment State Pager Adapter

java

android

fragment

fragmentstatepageradapter