Android ViewPager不显示Fragment

Question

我试图让我的ViewPager显示我的片段，然而，它似乎并没有完成这项工作。它只是没有显示任何东西，甚至没有高度。有人能告诉我，我错过了哪一步？感谢

main_activity.xml：

<android.support.design.widget.CoordinatorLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:background="@color/colorBackground">

    <android.support.v4.view.ViewPager
        android:id="@+id/viewpager"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:layout_above="@+id/bottomNavigation" />

    <com.aurelhubert.ahbottomnavigation.AHBottomNavigation
        android:id="@+id/bottomNavigation"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_gravity="bottom" />

</android.support.design.widget.CoordinatorLayout>

MainActivity.java：

public class MainActivity extends AppCompatActivity {

    private static final String TAG = "MainActivity";

    AHBottomNavigation bottomNavigation;
    ViewPager viewPager;

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

        setContentView(R.layout.activity_main);
        bottomNavigation = (AHBottomNavigation) findViewById(R.id.bottomNavigation);
        viewPager = (ViewPager) findViewById(R.id.viewpager);
        ViewPagerAdapter pagerAdapter = new ViewPagerAdapter(getSupportFragmentManager());

        // Buttom Navigation
        // Add items
        AHBottomNavigationItem item1 = new AHBottomNavigationItem("Rooms", R.drawable.ic_chatboxes);
        AHBottomNavigationItem item2 = new AHBottomNavigationItem("User", R.drawable.ic_contact_outline);
        bottomNavigation.addItem(item1);
        bottomNavigation.addItem(item2);
        // Customize Buttom Navigation
        bottomNavigation.setTitleState(AHBottomNavigation.TitleState.ALWAYS_SHOW);
        // Set colors
        bottomNavigation.setAccentColor(ContextCompat.getColor(this, R.color.colorAccent));
        bottomNavigation.setInactiveColor(ContextCompat.getColor(this, R.color.colorTabDefault));
        // Set background color
        bottomNavigation.setDefaultBackgroundColor(ContextCompat.getColor(this, R.color.colorBackground));
        bottomNavigation.setTranslucentNavigationEnabled(true);

        // Viewpager setup
        pagerAdapter.addFragment(new Rooms(), "Rooms");
        pagerAdapter.addFragment(new User(), "User");
        viewPager.setAdapter(pagerAdapter);
        viewPager.setCurrentItem(bottomNavigation.getCurrentItem());
        viewPager.addOnPageChangeListener(new ViewPager.OnPageChangeListener() {

            @Override
            public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {

            }

            @Override
            public void onPageSelected(int position) {
                bottomNavigation.setCurrentItem(position);
            }

            @Override
            public void onPageScrollStateChanged(int state) {

            }
        });
        bottomNavigation.setOnTabSelectedListener(new AHBottomNavigation.OnTabSelectedListener() {
            @Override
            public boolean onTabSelected(int position, boolean wasSelected) {
                viewPager.setCurrentItem(position, true);
                return true;
            }
        });
    }

ViewPagerAdapter.java：

public class ViewPagerAdapter extends FragmentPagerAdapter {
    private final List<Fragment> mFragmentList = new ArrayList<>();
    private final List<String> mFragmentTitleList = new ArrayList<>();
    private Fragment currentItem;

    public ViewPagerAdapter(FragmentManager manager) {
        super(manager);
    }

    @Override
    public Fragment getItem(int position) {
        return mFragmentList.get(position);
    }

    @Override
    public int getCount() {
        return mFragmentList.size();
    }

    public void addFragment(Fragment fragment, String title) {
        mFragmentList.add(fragment);
        mFragmentTitleList.add(title);
    }

    @Override
    public CharSequence getPageTitle(int position) {
        return mFragmentTitleList.get(position);
    }

    @Override
    public void setPrimaryItem(ViewGroup container, int position, Object object) {
        if (getCurrentItem() != object) {
            currentItem = ((Fragment) object);
        }
        super.setPrimaryItem(container, position, object);
    }

    public Fragment getCurrentItem() {
        return currentItem;
    }
}