TabLayout ViewPager Not Loading When Using Backsta

问题:

This question already has an answer here:

• Lifecycle of a replaced ViewPager and BackStack? 1 answer

I'm using a TabLayout in one of my fragments with a viewPager to switch between two fragments below the tabs.

When I click the FAB inside one of the lower fragments, I load a new fragment (for input).

However- when I press the BACK button, the TabLayout shows up but WITHOUT either of the lower fragments (represented by the pages).

So what am I doing wrong?

• and is there a better way to be swapping fragments?
• and is there a way to press the back button and get back to the viewPager Page that was showing?

Fragment with TabLayout: CustomTemplatesFragment

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
                         Bundle savedInstanceState) {
    // Inflate the layout for this fragment
    View view =  inflater.inflate(R.layout.fragment_custom_templates, container, false);
    final TabLayout tabLayout = (TabLayout) view.findViewById(R.id.tab_layout);
    tabLayout.addTab(tabLayout.newTab().setText(R.string.macro_tab));
    tabLayout.addTab(tabLayout.newTab().setText(R.string.lifestyle_tab));
    tabLayout.setTabGravity(TabLayout.GRAVITY_FILL);

    final ViewPager viewPager = (ViewPager) view.findViewById(R.id.pager);
    final CustomTemplatesPagerAdapter adapter = new CustomTemplatesPagerAdapter
            (getFragmentManager(), tabLayout.getTabCount());
    viewPager.setAdapter(adapter);
    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) {

        }

    });
    return view;
}

Pager Adapter: CustomTemplatePagerAdapter

public class CustomTemplatesPagerAdapter extends FragmentStatePagerAdapter {
int mNumOfTabs;

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

@Override
public Fragment getItem(int position) {

    switch (position) {
        case 0:
            CustomMacroFragment tab1 = new CustomMacroFragment();
            return tab1;
        case 1:
            CustomLifestyleFragment tab2 = new CustomLifestyleFragment();
            return tab2;
        default:
            return null;
    }
}

Lower Fragment with FAB: CustomMacroFragment

private void onFABClicked() {
    Fragment fragment = null;
    Class fragmentClass = MacroTemplateDetailFragment.class;
    try {
        fragment = (Fragment) fragmentClass.newInstance();
    } catch (Exception e) {
        e.printStackTrace();
    }


    // Insert the fragment by replacing any existing fragment
    FragmentManager fm = getActivity().getSupportFragmentManager();
    FragmentTransaction ft = fm.beginTransaction();
    ft.replace(R.id.flContent, fragment);
    ft.addToBackStack(null);
    ft.commit();
}

TabLayout/ViewPager XML

<LinearLayout
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical"
android:id="@+id/customLayout"
tools:context=".CustomTemplatesFragment">

<android.support.design.widget.TabLayout
    android:id="@+id/tab_layout"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:background="?attr/colorPrimary"
    android:elevation="6dp"
    android:theme="@style/ThemeOverlay.AppCompat.Dark.ActionBar"/>

<!--android:minHeight="?attr/actionBarSize"-->

<android.support.v4.view.ViewPager
    android:id="@+id/pager"
    android:layout_width="match_parent"
    android:layout_height="fill_parent"
    android:layout_below="@id/tab_layout"/>

Fragment with FAB XML

<android.support.design.widget.CoordinatorLayout
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:id="@+id/macroCoordinator"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context=".CustomMacroFragment">

<!-- using RecyclerView because of
https://guides.codepath.com/android/Floating-Action-Buttons -->
<android.support.v7.widget.RecyclerView
    android:id="@+id/rvMacrolist"
    android:layout_width="match_parent"
    android:layout_height="match_parent">
</android.support.v7.widget.RecyclerView>

<TextView
    android:id="@+id/emptyView"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    android:gravity="center_horizontal|center_vertical"
    android:visibility="gone"
    android:text="Please add a Macronutrient Template"/>

<!--https://guides.codepath.com/android/Floating-Action-Buttons-->
<android.support.design.widget.FloatingActionButton
    android:id="@+id/macroListFAB"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_gravity="bottom|right"
    android:layout_margin="@dimen/activity_margin"
    android:src="@drawable/ic_plus"
    app:layout_anchor="@id/rvMacrolist"
    app:layout_anchorGravity="bottom|right|end"
    app:layout_behavior=".utilities.behavior.ScrollAwareFABBehavior"/>

回答1:

I believe found the answer here: Lifecycle of a replaced ViewPager and BackStack?

Works for initial testing. Need to replace getFragmentManager() with getChildFragment Manager at the adapter

ViewPagerAdapter adapter = new ViewPagerAdapter(getChildFragmentManager());