Java 使用TabLayout片段[不重复]处理NavigationDrawer片段时出现问题

我有一个应用程序具有以下主要设置（不包括其他布局）：

main_display.xml：本质上是一个抽屉设置，带有一个框架布局，我用每个视图替换它

主刷新器片段：包含TabLayout和ViewPager，以及SwipeRefreshLayout和RecyclerView[注意：此RecyclerView由从网站上刮取的数据填充]

问题I

java.lang.NullPointerException:println需要一条消息。我不知道为什么这个变量是空的。我还收到了日志消息：
E/标记周期：MP2
何时应该是MP1（也称为我的第一个选项卡标题）。现在，我也问过类似的问题，但他们没有对我有用的答案，因此我请求帮助。对于如何使此设置正确运行，如有任何建议，将不胜感激

我的main_display.xml如下所示：

我的主显示类：

最后，我的GradeRefresherFragment课程的相关部分：

注意：问题不在于我的抓取代码，因为在我添加选项卡之前，它正在处理我的NavigationDrawer片段
println需要一条消息
通常意味着调用的是带有空参数的
Log
方法。除此之外，还不清楚到底是什么问题。@MikeM。然而，我意识到，我不清楚为什么这个参数是空的（很抱歉，我不清楚），我在那个代码中只看到一个
Log
调用，用来打印
位置，而这不应该造成这种情况。请发布堆栈跟踪。@MikeM。我用我的Scraper类的
doInBackground
部分更新了代码，这是
Log
调用的发源地您需要从参数
Bundle
中获取
Scraper
的
mMarkingPeriod
，而不是从
newInstance（）中设置的字段中获取。
<android.support.v4.widget.DrawerLayout
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:id="@+id/drawer_layout"
android:layout_width="match_parent"
android:layout_height="match_parent">
    <FrameLayout
        android:id="@+id/flContent"
        android:layout_width="0dp"
        android:layout_height="551dp"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toRightOf="parent"/>
    <android.support.design.widget.NavigationView
        android:id="@+id/nvView"
        android:layout_width="wrap_content"
        android:layout_height="match_parent"
        android:layout_gravity="start"
        android:background="#FF303030"
        app:headerLayout="@layout/navigation_header"
        app:menu="@menu/drawer_view" />
</android.support.v4.widget.DrawerLayout>

<android.support.constraint.ConstraintLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:paddingStart="0dp"
    android:paddingTop="0dp"
    tools:context="com.scyon.studentaid.MainDisplay">
    <include
        layout="@layout/toolbar"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:id="@+id/include" />
    <android.support.design.widget.TabLayout
        android:id="@+id/sliding_tabs"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        app:tabMode="fixed"
        tools:layout_editor_absoluteY="0dp"
        tools:layout_editor_absoluteX="8dp" />
    <android.support.v4.view.ViewPager
        android:id="@+id/viewpager"
        android:layout_width="0dp"
        android:layout_height="0dp"
        android:layout_weight="1"
        android:background="@android:color/white"
        tools:layout_editor_absoluteY="0dp"
        tools:layout_editor_absoluteX="16dp" />
    <android.support.v4.widget.SwipeRefreshLayout
        xmlns:android="http://schemas.android.com/apk/res/android"
        xmlns:app="http://schemas.android.com/apk/res-auto"
        xmlns:tools="http://schemas.android.com/tools"
        android:id="@+id/refresher"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        <com.scyon.studentaid.AnimatedRecyclerView
            android:id="@+id/grade_recycler"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:layout_gravity="center_horizontal"
        </com.scyon.studentaid.AnimatedRecyclerView>
    </android.support.v4.widget.SwipeRefreshLayout>

public class MarkingPeriodFragmentAdapter extends FragmentPagerAdapter {

private String [] tabTitles = new String[]{"MP1", "MP2", "MP3", "MP4"};
Context context;

public MarkingPeriodFragmentAdapter(FragmentManager fm, Context context) {
    super(fm);
    this.context = context;
}

@Override
public Fragment getItem(int position) {

    Log.e("Position", String.valueOf(position));
    return GradeRefresherFragment.newInstance(tabTitles[position]) ;
}

@Override
public int getCount() {
    return 4;
}

@Override
public CharSequence getPageTitle(int position) {
    return tabTitles[position];
}
}

public class MainDisplay extends AppCompatActivity {

DrawerLayout drawerLayout;
NavigationView navigationView;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.main_display);

    drawerLayout = (DrawerLayout)findViewById(R.id.drawer_layout);

    FragmentManager fragmentManager = getSupportFragmentManager();
    FragmentTransaction fragmentTransaction;

    fragmentTransaction = fragmentManager.beginTransaction();
    fragmentTransaction.replace(R.id.flContent, GradeRefresherFragment.newInstance("MP1"));
    fragmentTransaction.commit();

    navigationView = (NavigationView)findViewById(R.id.nvView);
    setupDrawerContents(navigationView);

}

@Override
public void onBackPressed() {
}

private void setupDrawerContents(NavigationView navigationView) {

    navigationView.setNavigationItemSelectedListener(new NavigationView.OnNavigationItemSelectedListener() {
        @Override
        public boolean onNavigationItemSelected(@NonNull MenuItem item) {
            displayView(item.getItemId());
            return true;
        }
    });
}

private void displayView (int viewID) {

    FragmentManager fragmentManager = getSupportFragmentManager();

    Fragment fragment;
    FragmentTransaction fragmentTransaction;


    switch (viewID) {

        case R.id.nav_gradebook_fragment:
            fragment = GradeRefresherFragment().newInstance("MP1");

            fragmentTransaction = fragmentManager.beginTransaction();
            fragmentTransaction.replace(R.id.flContent, fragment);
            fragmentTransaction.commit();
            break;

        case R.id.nav_shcedule_fragment:
            fragment = new ScheduleFragment();

            fragmentTransaction = fragmentManager.beginTransaction();
            fragmentTransaction.replace(R.id.flContent, fragment);
            fragmentTransaction.commit();
            break;

        case R.id.nav_logout_fragment:

            Intent intent = new Intent(getApplicationContext(), LoginScreen.class);

            SessionManager sessionManager = new SessionManager(getApplicationContext());
            sessionManager.logout();
            startActivity(intent);

            break;

        default:
            fragment = GradeRefresherFragment().newInstance("MP1");

            fragmentTransaction = fragmentManager.beginTransaction();
            fragmentTransaction.replace(R.id.flContent, fragment);
            fragmentTransaction.commit();
            break;
    }


    drawerLayout.closeDrawers();

}

public class GradeRefresherFragment extends Fragment{

Toolbar toolbar;
DrawerLayout mDrawer;
SwipeRefreshLayout swipeRefreshLayout;
ActionBarDrawerToggle mDrawerToggle;

ViewPager viewPager;
TabLayout tabLayout;

static String mMarkingPeriod;

public static GradeRefresherFragment newInstance(String markingPeriod){

    GradeRefresherFragment instance = new GradeRefresherFragment();

    Bundle arguments = new Bundle();
    arguments.putString("mp", markingPeriod);
    instance.setArguments(arguments);

    return instance;
}

@Override
public void onCreate(Bundle savedInstanceState) {

    new Scraper(getArguments().getString("mp")).execute();

    super.onCreate(savedInstanceState);
}

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

    View view = inflater.inflate(R.layout.main_refresher_fragment, container, false);

    toolbar = (Toolbar)view.findViewById(R.id.toolbar);
    AppCompatActivity activity = ((AppCompatActivity)getActivity());
    activity.setSupportActionBar(toolbar);
    activity.getSupportActionBar().setDisplayHomeAsUpEnabled(true);

    mDrawer = (DrawerLayout)getActivity().findViewById(R.id.drawer_layout);
    mDrawerToggle = new ActionBarDrawerToggle(getActivity(), mDrawer, toolbar, R.string.drawer_open, R.string.drawer_close);
    mDrawer.addDrawerListener(mDrawerToggle);

    mDrawerToggle.syncState();

    viewPager = (ViewPager)view.findViewById(R.id.viewpager);
    viewPager.setAdapter(new MarkingPeriodFragmentAdapter(getFragmentManager(), getActivity()));

    tabLayout = (TabLayout)view.findViewById(R.id.sliding_tabs);
    tabLayout.setupWithViewPager(viewPager);


    return view;
}
private class Scraper extends AsyncTask<String, Void, Wrapper> {

    String mMarkingPeriod;

    public Scraper(String markingPeriod) {
        mMarkingPeriod = markingPeriod;
    }

    @Override
    protected Wrapper doInBackground(String... strings) {
        Wrapper wrapper = new Wrapper();

        SessionManager sessionManager = new SessionManager(getContext());
        String username = sessionManager.getUsername();
        String password = sessionManager.getPassword();


        DataManager dataManager = new DataManager(username,password);
        Map<String, String> preLoginCookies = dataManager.getPreLoginCookies();
        Map<String, String> postLoginCookies = dataManager.getPostLoginCookies(preLoginCookies);

        Document doc = dataManager.getMPDocument(postLoginCookies,mMarkingPeriod);

        Log.e("Marking Period", mMarkingPeriod);

        if (doc == null){
            Log.e("doInBackground Check", "null");}

        Elements elements = doc.select(".cellRight");

        wrapper.document = doc;
        wrapper.elements = elements;

        return wrapper;
    }

04-15 23:59:27.883 7127-7127/com.scyon.studentaid E/Checkpoint: IsLoggedIn: true
04-15 23:59:28.429 7127-7127/com.scyon.studentaid E/Position: 0
04-15 23:59:28.429 7127-7127/com.scyon.studentaid E/Position: 1
04-15 23:59:28.502 7127-7127/com.scyon.studentaid E/RecyclerView: No adapter attached; skipping layout
04-15 23:59:28.503 7127-7127/com.scyon.studentaid E/RecyclerView: No adapter attached; skipping layout
04-15 23:59:28.503 7127-7127/com.scyon.studentaid E/RecyclerView: No adapter attached; skipping layout
04-15 23:59:29.671 7127-7282/com.scyon.studentaid E/Marking Period: MP1
04-15 23:59:29.680 7127-7127/com.scyon.studentaid E/Checkpoint: Iterating elements
04-15 23:59:29.681 7127-7127/com.scyon.studentaid E/Checkpoint: Setting up Recycler
04-15 23:59:30.886 7127-7313/com.scyon.studentaid E/Marking Period: MP1
04-15 23:59:30.888 7127-7127/com.scyon.studentaid E/Checkpoint: Iterating elements
04-15 23:59:30.889 7127-7127/com.scyon.studentaid E/Checkpoint: Setting up Recycler
04-15 23:59:32.024 7127-7334/com.scyon.studentaid E/Marking Period: MP2
04-15 23:59:32.024 7127-7334/com.scyon.studentaid E/doInBackground Check: null


--------- beginning of crash
04-15 23:59:32.026 7127-7334/com.scyon.studentaid E/AndroidRuntime: 
FATAL EXCEPTION: AsyncTask #3

Process: com.scyon.studentaid, PID: 7127

java.lang.RuntimeException: An error occurred while executing doInBackground()

at android.os.AsyncTask$3.done(AsyncTask.java:318)

at java.util.concurrent.FutureTask.finishCompletion(FutureTask.java:354)

at java.util.concurrent.FutureTask.setException(FutureTask.java:223)

at java.util.concurrent.FutureTask.run(FutureTask.java:242)

at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:243)

at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1133)

at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:607)

at java.lang.Thread.run(Thread.java:761)

Caused by: java.lang.NullPointerException: Attempt to invoke virtual 
method 'org.jsoup.select.Elements 
org.jsoup.nodes.Document.select(java.lang.String)' on a null object reference