Android TabLayout PagerAdapter 不显示第一个选项卡片段

Question

第一个选项卡不显示片段。

我正在使用以下方法来创建新标签。

public static void addNewTab(String TimelineName, String id) {
 TabLayout.Tab tab = tabs.newTab();
 tab.setText(TimelineName)
 tabs.addTab(tab);
 adapter.addTab(TimelineName);
}

adapter.add(Timeline) 是以下类中的一个方法：

public class TabsPagerAdapter extends PagerAdapter {

private final ArrayList<CharSequence> myTabList = new ArrayList<>();
int TabPosition = 0;
public static List<Bean_TimelineData> timelineData;
public static TimeLine_Adapter timeLineAdapter;
public static RecyclerView timelineRecyclerView;

// CREATE NEW TAB
public void addTab(String title) {
myTabList.add(title);
notifyDataSetChanged();
}

public void removeTab() {
if (!myTabList.isEmpty()) {
myTabList.remove(myTabList.size() - 1);
notifyDataSetChanged();
 }
}

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


@Override
public Object instantiateItem(ViewGroup container, int position) {
LinearLayout linearLayout = new LinearLayout(container.getContext());
timelineRecyclerView = new RecyclerView(container.getContext());

SwipeRefreshLayout swipeContainer;
timelineData = new ArrayList<Bean_TimelineData>();
timeLineAdapter = new TimeLine_Adapter(container.getContext(), timelineData, TabId);
timelineRecyclerView.setLayoutManager(new LinearLayoutManager(container.getContext()));

timelineRecyclerView.setAdapter(timeLineAdapter);
linearLayout.setOrientation(LinearLayout.VERTICAL);
linearLayout.setBackgroundColor(Color.parseColor("#f2f2f2"));

container.addView(linearLayout, ViewGroup.LayoutParams.MATCH_PARENT,
ViewGroup.LayoutParams.MATCH_PARENT);

LinearLayout.LayoutParams params = new LinearLayout.LayoutParams(
LinearLayout.LayoutParams.MATCH_PARENT,
LinearLayout.LayoutParams.WRAP_CONTENT
);

params.setMargins(0, 20, 0, 0);

timelineRecyclerView.setLayoutParams(params);

linearLayout.addView(timelineRecyclerView);

return linearLayout;
}

@Override
public boolean isViewFromObject(View view, Object object) {
return view == object;
}

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

@Override
public void destroyItem(ViewGroup container, int position, Object object) {
container.removeView((View) object);
}
}

但是我得到的结果是这样的：

让所有标签都正常工作：

如果我从 1 到 3 滑动标签，然后返回 1，片段会正确显示。

我查看了一些关于此的帖子，例如：This SO post

没有任何效果。

编辑

我想动态添加标签。 在第一个选项卡上，没有调用选项卡 pageradapter。这就是为什么第一个选项卡显示为空，其余所有工作正常。

Answer 1

使用FragmentPagerAdapter。

要将Fragment 添加到FragmentPagerAdapter，请关注它-

public class WeatherFragment extends Fragment {

    private Toolbar toolbar;
    private ViewPager viewPager;
    private ViewPagerAdapter viewPagerAdapter;
    private TabLayout tabLayout;

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

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

        //setup viewpager
        viewPager = (ViewPager) weatherFragment.findViewById(R.id.viewpager);
        tabLayout = (TabLayout) weatherFragment.findViewById(R.id.tabs);

        viewPagerAdapter = new ViewPagerAdapter(getChildFragmentManager());

        viewPager.setAdapter(viewPagerAdapter);
        tabLayout.setupWithViewPager(viewPager);

        return weatherFragment;
    }

和

public class ViewPagerAdapter extends FragmentPagerAdapter {
    public ViewPagerAdapter(FragmentManager fragmentManager) {
        super(fragmentManager);
    }

    @Override
    public Fragment getItem(int position) {
        if(position == 0) return new TodayTabFragment();
        if(position == 1) return new TomorrowTabFragment();
        if(position == 2) return new TenDaysTabFragment();

        throw new IllegalStateException("Unexpected position " + position);
    }

    @Override
    public int getCount() {
        return 3;
    }

    @Override
    public CharSequence getPageTitle(int position) {
        if(position == 0) return "Tab 1";
        if(position == 1) return "Tab 2";
        if(position == 2) return "Tab 3";
      
        throw new IllegalStateException("Unexpected position " + position);
    }
}

要获得对由 ViewPager 创建的 Fragment 的引用，请使用以下 findFragmentByTag 方案：

Fragment fragment = supportFragmentManager.findFragmentByTag("android:switcher:" + viewPager.getId() + ":" + fragmentPosition)

Fragment 的布局文件。

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:orientation="vertical"
    android:layout_width="match_parent"
    android:layout_height="wrap_content">

    <android.support.design.widget.TabLayout
        android:id="@+id/tabs"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        app:tabMode="fixed"
        android:background="@color/colorlightBlue"
        app:tabGravity="fill"
        app:tabTextColor="@color/colorWhite"
        app:tabSelectedTextColor="@color/colorWhite"
        app:tabIndicatorColor="@color/colorWhite"
        app:tabIndicatorHeight="2dp"/>


    <android.support.v4.view.ViewPager
        android:id="@+id/viewpager"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:scrollbarAlwaysDrawVerticalTrack="true"
        android:scrollbarAlwaysDrawHorizontalTrack="true"/>

</LinearLayout>

Answer 2

我认为最好的解决方案是更改您的实现，我更喜欢使用FragmentPageAdapter，它将为每个页面返回一个片段。然后，您可以单独控制每个片段内的内容。

主活动：

public class MainActivity extends AppCompatActivity {

    private ViewPager mViewPager;
    private TabLayout mTabLayout;

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

        Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
        setSupportActionBar(toolbar);

        mViewPager = (ViewPager) findViewById(R.id.pager);
        mViewPager.setAdapter(new TabsPager(this));


        mTabLayout = (TabLayout) findViewById(R.id.tabs);
        assert mTabLayout != null;
        mTabLayout.setupWithViewPager(mViewPager);
    }

还有我的适配器：

    private class TabsPager extends FragmentPagerAdapter {

        private final Context mContext;

        private Holder[] holders = new Holder[]{
                new Holder(getString(R.string.fragment_title), YourFragment.class),
                new Holder(getString(R.string.fragment_title2), YourFragment2.class)
        };

        class Holder {
            final CharSequence title;
            final Class<?> cls;

            Holder(CharSequence title, Class<?> cls) {
                this.title = title;
                this.cls = cls;
            }
        }

        TabsPager(FragmentActivity fa) {
            super(fa.getSupportFragmentManager());
            mContext = fa;
        }

        @Override
        public Fragment getItem(int position) {
            return Fragment.instantiate(mContext, holders[position].cls.getName());
        }

        @Override
        public int getCount() {
            return 2;
        }

        @Override
        public CharSequence getPageTitle(int position) {
            return holders[position].title;
        }
    }
}

您可以更改 Holder 类并根据需要添加任何片段。

Answer 3

如果你需要一个动态的 FragmentPagerAdapter，那么你可以这样做：

public class DynamicFragmentPagerAdapter extends PagerAdapter {
    private static final String TAG = "DynamicFragmentPagerAdapter";
  
    private final FragmentManager fragmentManager;
  
    public static abstract class FragmentIdentifier implements Parcelable {
        private final String fragmentTag;
        private final Bundle args;
      
        public FragmentIdentifier(@NonNull String fragmentTag, @Nullable Bundle args) {
            this.fragmentTag = fragmentTag;
            this.args = args;
        }
      
        protected FragmentIdentifier(Parcel in) {
            fragmentTag = in.readString();
            args = in.readBundle(getClass().getClassLoader());
        }

        @Override
        public void writeToParcel(Parcel dest, int flags) {
            dest.writeString(fragmentTag);
            dest.writeBundle(args);
        }
      
        protected final Fragment newFragment() {
            Fragment fragment = createFragment();
            Bundle oldArgs = fragment.getArguments();
            Bundle newArgs = new Bundle();
            if(oldArgs != null) {
                newArgs.putAll(oldArgs);
            }
            if(args != null) {
                newArgs.putAll(args);
            }
            fragment.setArguments(newArgs);
            return fragment;
        }

        protected abstract Fragment createFragment();
    }
  
    private ArrayList<FragmentIdentifier> fragmentIdentifiers = new ArrayList<>();

    private FragmentTransaction currentTransaction = null;

    private Fragment currentPrimaryItem = null;

    public DynamicFragmentPagerAdapter(FragmentManager fragmentManager) {
        this.fragmentManager = fragmentManager;
    }

    private int findIndexIfAdded(FragmentIdentifier fragmentIdentifier) {
        for (int i = 0, size = fragmentIdentifiers.size(); i < size; i++) {
            FragmentIdentifier identifier = fragmentIdentifiers.get(i);
            if (identifier.fragmentTag.equals(fragmentIdentifier.fragmentTag)) {
                return i;
            }
        }
        return -1;
    }

    public void addFragment(FragmentIdentifier fragmentIdentifier) {
        if (findIndexIfAdded(fragmentIdentifier) < 0) {
            fragmentIdentifiers.add(fragmentIdentifier);
            notifyDataSetChanged();
        }
    }

    public void removeFragment(FragmentIdentifier fragmentIdentifier) {
        int index = findIndexIfAdded(fragmentIdentifier);
        if (index >= 0) {
            fragmentIdentifiers.remove(index);
            notifyDataSetChanged();
        }
    }

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

    @Override
    public void startUpdate(@NonNull ViewGroup container) {
        if (container.getId() == View.NO_ID) {
            throw new IllegalStateException("ViewPager with adapter " + this
                    + " requires a view id");
        }
    }

    @SuppressWarnings("ReferenceEquality")
    @NonNull
    @Override
    public Object instantiateItem(@NonNull ViewGroup container, int position) {
        if (currentTransaction == null) {
            currentTransaction = fragmentManager.beginTransaction();
        }
        final FragmentIdentifier fragmentIdentifier = fragmentIdentifiers.get(position);
        // Do we already have this fragment?
        final String name = fragmentIdentifier.fragmentTag;
        Fragment fragment = fragmentManager.findFragmentByTag(name);
        if (fragment != null) {
            currentTransaction.attach(fragment);
        } else {
            fragment = fragmentIdentifier.newFragment();
            currentTransaction.add(container.getId(), fragment, fragmentIdentifier.fragmentTag);
        }
        if (fragment != currentPrimaryItem) {
            fragment.setMenuVisibility(false);
            fragment.setUserVisibleHint(false);
        }
        return fragment;
    }

    @Override
    public void destroyItem(@NonNull ViewGroup container, int position, @NonNull Object object) {
        if (currentTransaction == null) {
            currentTransaction = fragmentManager.beginTransaction();
        }
        currentTransaction.detach((Fragment) object);
    }

    @SuppressWarnings("ReferenceEquality")
    @Override
    public void setPrimaryItem(@NonNull ViewGroup container, int position, @NonNull Object object) {
        Fragment fragment = (Fragment) object;
        if (fragment != currentPrimaryItem) {
            if (currentPrimaryItem != null) {
                currentPrimaryItem.setMenuVisibility(false);
                currentPrimaryItem.setUserVisibleHint(false);
            }
            fragment.setMenuVisibility(true);
            fragment.setUserVisibleHint(true);
            currentPrimaryItem = fragment;
        }
    }

    @Override
    public void finishUpdate(@NonNull ViewGroup container) {
        if (currentTransaction != null) {
            currentTransaction.commitNowAllowingStateLoss();
            currentTransaction = null;
        }
    }

    @Override
    public boolean isViewFromObject(@NonNull View view, @NonNull Object object) {
        return ((Fragment) object).getView() == view;
    }

    @Override
    public Parcelable saveState() {
        Bundle bundle = new Bundle();
        bundle.putParcelableArrayList("fragmentIdentifiers", fragmentIdentifiers);
        return bundle;
    }

    @Override
    public void restoreState(Parcelable state, ClassLoader loader) {
        Bundle bundle = ((Bundle)state);
        bundle.setClassLoader(loader);
        fragmentIdentifiers = bundle.getParcelableArrayList("fragmentIdentifiers");
    }
}