在FragmentTransaction.replace()后跟后退按钮后,不会重新创建ViewPager片段

Question

我正在尝试实现保存和恢复状态,但是当用Fragmenta 替换main PreferenceFragment然后按下后退按钮时遇到问题.我的主要Fragment包括ViewPager一个FragmentPagerAdapter用3 Fragments来刷卡.点击后退按钮后,没有调用Fragment.onCreateView()我的3 Fragment秒的回调.我已经尝试了所有我在这里遇到的解决方案,但我无法解决这个问题.

另一个可能需要注意的重要事项是,我的3s ViewPager Fragment的数据存储在单独的类中,这些类是实例化的,可以通过Activity.3 Fragments包含RecyclerView用于列出大量数据的s.这样做是为了清洁,但也是为了使这些数据持续存在Activity.这可能不是问题,因为它在启动应用程序时工作正常,但也因为主要问题是我Fragments没有重新创建.

意外行为:

在应用程序创建时,一切正常,但是当我用另一个替换我的main Fragment(包含ViewPagera FragmentPagerAdapter),然后按下后退按钮时,不会重新创建Fragments中的s ViewPager.在onCreateView()我的主要的Fragment 被调用.

问题:

我错过了什么？是否还应该创建一些其他回调？我应该在哪里以及如何重建Fragments？

我试过了什么:

1. 改变了FragmentAdapter使用,但我真的应该使用这里getSupportFragmentManager()的解决方案.

编辑:使用错误FragmentManager实际上是我的麻烦的来源.请参阅下面的答案.

2. 添加 @Override public int getItemPosition(Object object) {return POSITION_NONE;}到FragmentPagerAdapter,如此处所示.
3. 从变化FragmentPagerAdapter到FragmentStatePagerAdapter哪个不应该的问题在这里,因为据我所知.内部FragmentStatePagerAdapter实际上保留了Fragments,但它们不会重新呈现.
4. Fragment使用调用FragmentTransaction它的时候添加主后部,onCreateView()并在其中的几个其他回调中添加Fragment,见MMMainFragment下文.
5. 各种其他事情.

我的MainFragment类具有相应的XML布局

public class MMMainFragment extends Fragment
{
    private MMViewPager mMMViewPager = null;

    @Nullable
    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState)
    {
        // Note that this method IS called when the back button is pressed.
        // I have tried setting the content back to this instance in several places.

        View view = inflater.inflate(R.layout.mm_main_fragment, container, false);

        // Setup ViewPager.
        mMMViewPager = (MMViewPager) view.findViewById(R.id.mm_pager);
        TabLayout tabLayout = (TabLayout) view.findViewById(R.id.mm_tablayout);
        tabLayout.setupWithViewPager(mMMViewPager);

        return view;
    }

    public MMViewPager getMMViewPager()
    {
        return mMMViewPager;
    }
}

mm_main_fragment.xml

<?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="match_parent" >

    <android.support.design.widget.TabLayout
        android:id="@+id/mm_tablayout"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        app:tabMode="scrollable" />

    <com.mycompany.myapp.gui.mmpager.MMViewPager
        android:id="@+id/mm_pager"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:layout_weight="1" />


</LinearLayout>

然后,Activity.onCreate()我只是做:

// Insert Main Fragment.
FragmentManager fragmentManager = getSupportFragmentManager();
fragmentManager.beginTransaction()
        .replace(R.id.mm_content_frame, new MMMainFragment())
        .commit();

这里mm_content_frame是FrameLayout哪里替换和删除Fragment秒.然后,当按下查看首选项的按钮时,我在下面运行下面的代码片段Activity.我将它添加Fragment到backstack以便能够使用后退按钮.

public void showSettingsFragment()
{
    getSupportActionBar().setTitle(getString(R.string.mm_drawer_settings));
    getSupportFragmentManager().beginTransaction()
            .replace(R.id.mm_content_frame, new MMPreferencesFragment(), FragmentConstants.SETTINGS_FRAGMENT_TAG)
            .addToBackStack(null)
            .commit();
}

MMViewPager分组:

public class MMViewPager extends ViewPager
{
    private MMActivity mMMActivity;
    private MMPagerAdapter mMMPagerAdapter;

    public MMViewPager(Context context, AttributeSet attrs)
    {
        super(context, attrs);
        mMMActivity = (MMActivity) context;
        mMMPagerAdapter = new MMPagerAdapter(mMMActivity.getSupportFragmentManager(), mMMActivity);

        this.setOffscreenPageLimit(PagerConstants.OFFSCREEN_PAGE_LIMIT);
        this.setAdapter(mMMMPagerAdapter);
        this.setCurrentItem(PagerConstants.PAGE_FILTER_RECIPES);
    }
}

MMPagerAdapter类,目前是FragmentStatePagerAdapter:

public class MMPagerAdapter extends FragmentStatePagerAdapter
{
    private MMActivity mMMActivity;

    public MMPagerAdapter(FragmentManager fragmentManager, MMActivity mmActivity)
    {
        super(fragmentManager);
        mMMActivity = mmActivity;
    }

    @Override
    public Fragment getItem(int position)
    {
        switch (position)
        {
            case PagerConstants.PAGE_FILTER_RECIPES:
                return new FilteredRecipesFragment();

            case PagerConstants.PAGE_SELECTED_RECIPES:
                return new SelectedRecipesFragment();

            case PagerConstants.PAGE_SHOPPING_LIST:
                return new ShoppingListFragment();

            default:
                return null;
        }
    }

    @Override
    public int getCount()
    {
        return PagerConstants.NUMBER_OF_PAGES; // 3
    }

    @Override
    public CharSequence getPageTitle(int position)
    {
        switch (position)
        {
            case PagerConstants.PAGE_FILTER_RECIPES:
                return mMMActivity.getResources().getString(R.string.mm_title_recipe_filter_fragment);

            case PagerConstants.PAGE_SELECTED_RECIPES:
                return mMMActivity.getResources().getString(R.string.mm_title_selected_recipes_fragment);

            case PagerConstants.PAGE_SHOPPING_LIST:
                return mMMActivity.getResources().getString(R.string.mm_title_shopping_list_fragment);

            default:
                return "Tab";
        }
    }
}

供参考,这里也是主要的布局Activity:

<?xml version="1.0" encoding="utf-8"?>
<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/mm_drawer_layout"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <!-- Source: http://developer.android.com/training/implementing-navigation/nav-drawer.html -->
    <!-- The main content view -->
    <RelativeLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent">

        <!-- Source: http://android-developers.blogspot.in/2014/10/appcompat-v21-material-design-for-pre.html -->
        <android.support.v7.widget.Toolbar
            xmlns:android="http://schemas.android.com/apk/res/android"
            android:id="@+id/mm_toolbar"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:minHeight="?attr/actionBarSize"
            android:layout_alignParentTop="true"
            style="@style/MMActionBar"
            app:theme="@style/ThemeOverlay.AppCompat.Dark.ActionBar"
            app:popupTheme="@style/ThemeOverlay.AppCompat.Light" />

        <!-- The FrameLayout where I replace Fragments -->
        <FrameLayout
            android:id="@+id/mm_content_frame"
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            android:layout_below="@id/mm_toolbar"/>

    </RelativeLayout>


    <ListView
        android:id="@+id/mm_drawer_listview"
        android:layout_width="260dp"
        android:layout_height="match_parent"
        android:paddingLeft="16dp"
        android:paddingRight="16dp"
        android:paddingStart="16dp"
        android:layout_gravity="start"
        android:choiceMode="singleChoice"
        android:divider="@android:color/transparent"
        android:dividerHeight="0dp"
        android:background="@color/mm_white" />

</android.support.v4.widget.DrawerLayout>

Answer 1

经过几天的努力,我意识到问题实际上是我把错误FragmentManager传给了ViewPager.确实应该使用它FragmentManager返回Fragment.getChildFragmentManager().这是有道理的,因为它Fragment本身就存储了孩子Fragment的状态ViewPager.我不知道为什么我不能让之前的工作,但现在的应用程序的生命周期,工作正常,在我的主要以下设置Fragment的onCreate()方法:

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

    mMMActivity = (MMActivity) container.getContext();
    mMMActivity.getSupportActionBar().setTitle(getString(R.string.mm_toolbar_title_main_fragment));

    // Setup ViewPager.
    mViewPager = (ViewPager) view.findViewById(R.id.mm_pager);
    mAdapter = new MMPagerAdapter(getChildFragmentManager(), mMMActivity); // <-- This is the key
    mViewPager.setAdapter(mAdapter);
    mViewPager.setOffscreenPageLimit(PagerConstants.OFFSCREEN_PAGE_LIMIT);
    mViewPager.setCurrentItem(PagerConstants.PAGE_FILTER_RECIPES);

    // Setup TabLayout.
    TabLayout tabLayout = (TabLayout) view.findViewById(R.id.mm_tablayout);
    tabLayout.setupWithViewPager(mViewPager);

    return view;
}

这也是另一个问题的解决方案.作为旁注,我使用这个解决方案来获取Fragment我的s ViewPager并且它与LifeCycle一起工作得很好.

测试应用:

在这个问题的研究中,我为此创建了一个测试应用程序.有兴趣的人可以从这里克隆它.它有难看的颜色.