Android: TabLayout 不显示任何选项卡

Question

第一次使用 com.android.support:design:23.1.1，在使用 TabLayout 时遇到了一些问题。

我的应用基本上是这样设置的：

一个名为 LandingActivity 的主要 activity 有一个带有菜单项的 DrawerLayout。
选择菜单项时，我将不同的Fragment加载到LandingActivity中的FrameLayout中。
一些加载的片段应该在顶部显示标签，一些不应该。

我的问题是，在应该在顶部显示标签的 Fragment 上，它在导航栏中有额外的 space，就像它应该在那里有标签一样，但没有显示。

代码：

activity_landing.xml

<android.support.v4.widget.DrawerLayout
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
android:id="@+id/drawer_layout"
android:layout_width="match_parent"
android:layout_height="match_parent">

<!-- This LinearLayout represents the contents of the screen  -->
<LinearLayout
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical">

    <!-- The ActionBar displayed at the top -->
    <include
        layout="@layout/tool_bar"
        android:layout_width="match_parent"
        android:layout_height="wrap_content" />

    <!-- The main content view where fragments are loaded -->
    <FrameLayout
        android:id="@+id/flContent"
        android:layout_width="match_parent"
        android:layout_height="match_parent" />
</LinearLayout>

<!-- The navigation drawer that comes from the left -->
<!-- Note that `android:layout_gravity` needs to be set to 'start' -->
<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="@android:color/white"
    app:menu="@menu/drawer" />

我加载片段的 LandingActivity：

 public void selectDrawerItem(MenuItem menuItem) {
    // Create a new fragment and specify the planet to show based on
    // position
    Fragment fragment = null;

    switch(menuItem.getItemId()) {
        case R.id.drawer_home:
            fragment = HomeFragment.newInstance();
            break;
        case R.id.drawer_customize:
            fragment = CustomizeFragment.newInstance();
            break;
        default:
            fragment = HomeFragment.newInstance();
    }

    // Insert the fragment by replacing any existing fragment
    FragmentManager fragmentManager = getSupportFragmentManager();
    fragmentManager.beginTransaction().replace(R.id.flContent, fragment).commit();

home_fragment.xml（有标签的）

<android.support.design.widget.AppBarLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
xmlns:app="http://schemas.android.com/apk/res-auto"
android:layout_width="match_parent"
android:layout_height="match_parent">

<android.support.design.widget.TabLayout
    android:id="@+id/tabLayout"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    app:tabMode="fixed"
    app:tabGravity="fill"
   />

<android.support.v4.view.ViewPager
    android:id="@+id/viewpager"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:background="@android:color/white"/>

HomeFragment.java

public class HomeFragment extends Fragment {

public static HomeFragment newInstance() {
    Bundle args = new Bundle(); alreadySelectedFollowingInfo);

    HomeFragment fragment = new HomeFragment();
    fragment.setArguments(args);
    return fragment;
}

public HomeFragment() {

}

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

    final View v = inflater.inflate(R.layout.fragment_home, container, false);

    final TabLayout tabLayout = (TabLayout) v.findViewById(R.id.tabLayout);
    tabLayout.addTab(tabLayout.newTab().setText("One"));
    tabLayout.addTab(tabLayout.newTab().setText("Two"));
    final ViewPager viewPager = (ViewPager) v.findViewById(R.id.viewpager);

    viewPager.setAdapter(new PagerAdapter
            (getFragmentManager(), tabLayout.getTabCount()));
    viewPager.addOnPageChangeListener(new TabLayout.TabLayoutOnPageChangeListener(tabLayout));
    tabLayout.setOnTabSelectedListener(new TabLayout.OnTabSelectedListener() {
        @Override
        public void onTabSelected(TabLayout.Tab tab) {
            viewPager.setCurrentItem(tab.getPosition());
        }

        @Override
        public void onTabUnselected(TabLayout.Tab tab) {

        }

        @Override
        public void onTabReselected(TabLayout.Tab tab) {

        }
    });

    tabLayout.post(new Runnable() {
        @Override
        public void run() {
            tabLayout.setupWithViewPager(viewPager);
        }
    });

    return inflater.inflate(R.layout.fragment_home, container, false);
}

public class PagerAdapter extends FragmentStatePagerAdapter {
    int mNumOfTabs;

    public PagerAdapter(FragmentManager fm, int NumOfTabs) {
        super(fm);
        this.mNumOfTabs = NumOfTabs;
    }

    @Override
    public Fragment getItem(int position) {

        switch (position) {
            case 0:
                BlogFragment tab1 = BlogFragment.newInstance();
                return tab1;
            case 1:
                TrendingFragment tab2 = TrendingFragment.newInstance();
                return tab2;
            default:
                return null;
        }
    }

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

}

可能不相关，但 tool_bar.xml 用于 activity_landing.xml

<android.support.v7.widget.Toolbar
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
android:id="@+id/toolbar"
android:layout_height="wrap_content"
android:layout_width="match_parent"
android:fitsSystemWindows="true"
android:minHeight="?attr/actionBarSize"
app:theme="@style/ThemeOverlay.AppCompat.Dark.ActionBar"
android:background="?attr/colorPrimary">

这就是我的全部。无法弄清楚发生了什么。

编辑：

新代码：

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

    final View v = inflater.inflate(R.layout.fragment_home, container, false);



    ViewPager viewPager = (ViewPager) v.findViewById(R.id.viewpager);
    setupViewPager(viewPager);

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



    return v;
}

private void setupViewPager(ViewPager viewPager) {
    PagerAdapter adapter = new PagerAdapter(getFragmentManager());
    adapter.addFragment(BlogFragment.newInstance(), "ONE");
    adapter.addFragment(TrendingFragment.newInstance(), "TWO");
    viewPager.setAdapter(adapter);
}

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

    public PagerAdapter(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);
    }
}

Answer 1

return inflater.inflate(R.layout.fragment_home, container, false);

在您的 onCreateView 中意味着您 return 一个没有任何初始化代码的新膨胀的主页片段。

您应该 return 访问您在 onCreateView 开头创建的视图：

return v;

提供选项卡标题的示例 PagerAdapter：

public class PagerAdapter extends FragmentPagerAdapter {
    private final List<Fragment> mFragments = new ArrayList<>();
    private final List<String> mFragmentTitles = new ArrayList<>();

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

    public void addFragment(Fragment fragment, String title) {
        mFragments.add(fragment);
        mFragmentTitles.add(title);
    }

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

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

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

因此，您重构的 onCreateView 代码将类似于：

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

    View v = inflater.inflate(R.layout.fragment_home, container, false);

    final TabLayout tabLayout = (TabLayout) v.findViewById(R.id.tabLayout);
    final ViewPager viewPager = (ViewPager) v.findViewById(R.id.viewpager);
    PagerAdapter adapter = new PagerAdapter(getFragmentManager());
    adapter.addFragment(BlogFragment.newInstance(), "One");
    adapter.addFragment(TrendingFragment.newInstance(), "Two");

    viewPager.setAdapter(adapter);
    tabLayout.post(new Runnable() {
        @Override
        public void run() {
            tabLayout.setupWithViewPager(viewPager);
        }
    });


    return v;
}

Answer 2

Return 您在 returning

时的初始化 infleted 视图

return inflater.inflate(R.layout.fragment_home, container, false);

而您应该return 从 onCreateView 的第一行查看 v

final View v = inflater.inflate(R.layout.fragment_home, container, false);

Android: TabLayout 不显示任何选项卡

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