Android TabLayout ViewPager 在返回栈中无法加载选项卡片段。

Question

我已经设置了一个选项卡视图，每个选项卡都使用ViewPager具有自定义的片段。这是我的代码：

持有碎片

public class FragInboxMainView extends Fragment implements CGFragment {
    private CGController controller;
    private CGFragment thisFragment;

    @Bind(R.id.inboxViewPager)ViewPager inboxViewPager;
    @Bind(R.id.inboxTabs)TabLayout inboxTabLayout;
    @Bind(R.id.inbox_progress_wheel)ProgressWheel inboxProgressWheel;

    public FragInboxMainView(){}

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

        View rootView = inflater.inflate(R.layout.fragment_inbox_mainview, container, false);
        ButterKnife.bind(this, rootView);
        thisFragment = this;
        Globals g = Globals.getInstance();
        /** Show loading spinner */
        this.inboxProgressWheel.setBarColor(ContextCompat.getColor(controller.getContext(), g.getUserObject().getUserThemeColor()));
        this.inboxProgressWheel.setVisibility(View.VISIBLE);
        /** Display the profile information based off the ID */
        controller.displayInbox(thisFragment);

        return rootView;
    }


    public void hideProgressSpinner() {
        this.inboxProgressWheel.setVisibility(View.GONE);
    }


    public ViewPager getInboxViewPager() {
        return this.inboxViewPager;
    }

    public TabLayout getInboxTabLayout() {
        return this.inboxTabLayout;
    }
}

它的布局文件。

<?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"
              xmlns:wheel="http://schemas.android.com/apk/res-auto"
              android:layout_width="match_parent"
              android:layout_height="match_parent"
              android:orientation="vertical">
    <android.support.design.widget.TabLayout
        android:id="@+id/inboxTabs"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        app:tabMode="scrollable" />
    <com.pnikosis.materialishprogress.ProgressWheel
        android:id="@+id/inbox_progress_wheel"
        android:layout_width="80dp"
        android:layout_height="80dp"
        android:layout_gravity="center"
        wheel:matProg_barColor="#5588FF"
        wheel:matProg_progressIndeterminate="true"
        android:visibility="gone"/>


    <android.support.v4.view.ViewPager
        android:id="@+id/inboxViewPager"
        android:layout_width="match_parent"
        android:layout_height="0px"
        android:layout_weight="1"
        android:background="@android:color/white" />
</LinearLayout>

选项卡片段和其布局文件

<?xml version="1.0" encoding="utf-8"?>
<android.support.design.widget.CoordinatorLayout
    android:id="@+id/main_content"
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <com.baoyz.widget.PullRefreshLayout
        android:id="@+id/tabPullRefresh"
        android:layout_width="match_parent"
        android:layout_height="match_parent">
    <view
        android:id="@+id/tabRecyclerHolder"
        class="android.support.v7.widget.RecyclerView"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:paddingTop="8dp"
        android:paddingBottom="8dp"
        android:clipToPadding="false"
        android:layout_centerInParent="true"/>

    </com.baoyz.widget.PullRefreshLayout>
    <com.melnykov.fab.FloatingActionButton
        android:id="@+id/tabFab"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_gravity="bottom|right"
        android:layout_margin="16dp"
        android:src="@mipmap/ic_add_white"/>
</android.support.design.widget.CoordinatorLayout>

public class TabRecyclerHolder extends Fragment {

    @Bind(R.id.tabRecyclerHolder) RecyclerView tabRecyclerHolder;
    @Bind(R.id.tabPullRefresh) PullRefreshLayout tabPullRefresh;
    @Bind(R.id.tabFab) FloatingActionButton recyclerFab;

    private String tabTitle = "Title";


    public TabRecyclerHolder(){}

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

        View rootView = inflater.inflate(R.layout.tab_recycler_holder, container, false);

        ButterKnife.bind(this, rootView);

        recyclerFab.hide(false);

        tabPullRefresh.setRefreshStyle(PullRefreshLayout.STYLE_MATERIAL);

        return rootView;
    }

    public RecyclerView getTabRecyclerHolder() {
        return this.tabRecyclerHolder;
    }

    public FloatingActionButton getRecyclerFab() {
        return this.recyclerFab;
    }

    public String getTabTitle() {
        return this.tabTitle;
    }

    public void setTabTitle(String title) {
        this.tabTitle = title;
    }

    public PullRefreshLayout getTabPullRefresh() {
        return this.tabPullRefresh;
    }
}

我的标签适配器

public class TabPagerAdapter extends FragmentStatePagerAdapter {

    private CGController controller;
    private List<Object> items;

    public TabPagerAdapter(FragmentManager fm, CGController controller, List<Object> items) {
        super(fm);
        this.controller = controller;
        this.items = items;
    }

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

    @Override
    public Fragment getItem(int num) {
        return (TabRecyclerHolder)items.get(num);
    }

    @Override
    public String getPageTitle(int num){
        return ((TabRecyclerHolder)items.get(num)).getTabTitle();
    }
}

处理代码。

public void viewInbox() {
    /** Set up the views */
    receivedHolder = new TabRecyclerHolder();
    receivedHolder.setTabTitle(Constants.TAB_INBOX_RECEIVED);
    sentHolder = new TabRecyclerHolder();
    sentHolder.setTabTitle(Constants.TAB_INBOX_SENT);

    tabs.add(receivedHolder);
    tabs.add(sentHolder);

    /** Set up the tabs */
    final ViewPager inboxViewPager = inboxFragment.getInboxViewPager();
    TabLayout inboxTabLayout = inboxFragment.getInboxTabLayout();

    /** Set the adapter for the view pager */
    inboxViewPager.setAdapter(new TabPagerAdapter(inboxFragment.getChildFragmentManager(), controller, tabs));
    /** set up the tab look and feel */
    inboxTabLayout.setTabGravity(TabLayout.GRAVITY_FILL);
    inboxTabLayout.setTabMode(TabLayout.MODE_FIXED);

    inboxViewPager.setOffscreenPageLimit(3);
    inboxViewPager.addOnPageChangeListener(new TabLayout.TabLayoutOnPageChangeListener(inboxTabLayout));
    inboxTabLayout.setOnTabSelectedListener(new TabLayout.OnTabSelectedListener() {
        @Override
        public void onTabSelected(TabLayout.Tab tab) {
            inboxViewPager.setCurrentItem(tab.getPosition());
        }

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

        }

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

        }
    });

    /** And, display! */
    inboxTabLayout.setupWithViewPager(inboxViewPager);

    receivedAdapter = new RecyclerListAdapter(controller, items);
    final RecyclerView receivedList = receivedHolder.getTabRecyclerHolder();
    receivedList.setLayoutManager(new LinearLayoutManager(controller.getContext()));
    receivedList.setAdapter(receivedAdapter);
}

有一些代码我省略了，但它与问题无关。 当最初查看该片段时，代码完美运行。然而，由于我的应用程序只包含一个活动并且仅替换每个导航到的片段的内容视图，因此每个片段都被添加到后退栈中，然后在按下后退按钮时弹出。我的问题是，当返回到这个片段时，选项卡内部的视图没有被填充，这意味着无法访问任何元素（因此，在尝试显示recyclerview等数据时，应用程序会崩溃）。

我查看了这个问题：TabLayout ViewPager Not Loading When Using Backstack并实施了它的建议（使用getChildFragmentManager()设置页面适配器），但这并没有解决我的问题。

希望得到帮助！

- Matt Davis

---

尝试访问应该在选项卡内填充的元素时，出现java.lang.NullPointerException错误。如果我删除任何尝试访问内部片段的代码，并只是让它显示而不崩溃，则选项卡内将什么也不显示。 - Matt Davis

该片段显示并展示了加载旋转器，但当应用程序下载完所有数据并尝试告诉旋转器隐藏时，它找不到它。 - Matt Davis

我已删除我的评论，以免混淆您的问题。尝试记录viewInbox()方法，并确保在片段重新创建时调用它。 - user

我不知道你的代码出了什么问题。最好的办法是在viewInbox()函数的开头设置一个断点，然后通过调试器逐步执行代码，确保数据和片段都没有问题。 - user

在调试器中瞎搞 - 当我最初查看片段并尝试从TabRecyclerHolder获取数据时，调试器给出了关于该对象的以下信息：TabRecyclerHolder{ef0cb89 #0 id=0x7f0d00bd}。它还显示pullrefresh也有一个对象实例。 然而，当导航到其他地方，然后通过片段堆栈返回时，它会给我这个：TabRecyclerHolder{1a8a8e64}，对象内部的任何UI变量都为null。因此，看起来它没有再次填充视图。 - Matt Davis

Answer 1

将这个代码：public View onCreateView(LayoutInflater inflater,... 改为 public void onViewCreated (View view, Bundle savedInstanceState) 这样你就会得到类似下面的代码：

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
                         Bundle savedInstanceState) {        
    return inflater.inflate(R.layout.tab_recycler_holder, container, false);
}

那么

@Override
public void onViewCreated (View view, Bundle savedInstanceState){
     ButterKnife.bind(this, view);
    recyclerFab.hide(false);
    tabPullRefresh.setRefreshStyle(PullRefreshLayout.STYLE_MATERIAL);
    ...

看看它是否有帮助

- Elltz

---

很遗憾，没有好运气 =( - Matt Davis

Answer 2

扩展 FragmentStatePagerAdapter 为 TabPagerAdapter，如下所示：

FragmentStatePagerAdapter(fragmentManager, BEHAVIOR_RESUME_ONLY_CURRENT_FRAGMENT)

- Divya