RecyclerView：没有附加适配器；跳过布局？我该怎么办？

Question

今天我的应用程序遇到了这个问题；我想说的是，我在 StackOverflow 上阅读了几乎所有其他问题，但什么都没有，总是同样的问题。homepage.java（主类） public class homepage extends AppCompatActivity {    private SectionsPagerAdapter mSectionsPagerAdapter;    private ViewPager mViewPager;    @Override    protected void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.activity_homepage);        Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);        setSupportActionBar(toolbar);        mSectionsPagerAdapter = new SectionsPagerAdapter(getSupportFragmentManager());        mViewPager = (ViewPager) findViewById(R.id.container);        mViewPager.setAdapter(mSectionsPagerAdapter);        TabLayout tabLayout = (TabLayout) findViewById(R.id.tabs);        mViewPager.addOnPageChangeListener(new TabLayout.TabLayoutOnPageChangeListener(tabLayout));        tabLayout.addOnTabSelectedListener(new TabLayout.ViewPagerOnTabSelectedListener(mViewPager));    }    @Override    public boolean onCreateOptionsMenu(Menu menu) {        getMenuInflater().inflate(R.menu.menu_homepage, menu);        return true;    }    @Override    public boolean onOptionsItemSelected(MenuItem item) {        int id = item.getItemId();        if (id == R.id.action_settings) {            return true;        }        return super.onOptionsItemSelected(item);    }    public static class PlaceholderFragment extends Fragment {        private static final String ARG_SECTION_NUMBER = "section_number";        public PlaceholderFragment() {        }        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;        }        }    }