Java 在片段中创建选项卡

我有一个包含一个主要活动的应用程序，它有一个导航面板在片段之间切换。在一个片段中，我希望有选项卡在其他片段之间切换。我已经创建了一个单独的片段，可以从导航面板访问：

public class EventsTabsFragment extends Fragment
{
    private TabLayout events_tabs;
    private ViewPager events_pager;
    private static int int_items = 2;

    @Nullable
    @Override
    public View onCreateView(@NonNull LayoutInflater inflater, @Nullable final ViewGroup container, @Nullable Bundle savedInstanceState)
    {
        //the inflate() method takes the layout you wanna show as the first parameter
        View view = inflater.inflate(R.layout.event_tabs, container, false);

        //tabs for our fragment
        events_tabs = view.findViewById(R.id.events_tabs);
        events_pager = view.findViewById(R.id.events_pager);

        events_pager.setAdapter(new MyAdapter(getChildFragmentManager()));

        events_tabs.post(new Runnable() {
            @Override
            public void run() {
                events_tabs.setupWithViewPager(events_pager);
            }
        });

        return view;
    }

    class MyAdapter extends FragmentStatePagerAdapter
    {
        public MyAdapter(FragmentManager fm)
        {
            super(fm);
        }

        /**
         * I WANNA SWITCH BETWEEN FRAGMENTS HERE
         */
        @Override
        public Fragment getItem(int position)
        {
            switch (position) {
                case 0:
                    return new EventsActivity();
            }
            return null;
        }

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

        /**
         * This method returns the title of the tab according to the position.
         */
        @Override
        public CharSequence getPageTitle(int position)
        {
            switch (position)
            {
                case 0:
                    String main_events = "Events";
                    return main_events;
                case 1:
                    String pending = "Pending event invites";
                    return pending;
            }
            return null;
        }
    }
}

它的xml（event_tabs.xml）使用

TabLayout

和

ViewPager

，如下所示：

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:layout_height="match_parent"
    android:layout_width="match_parent">

    <com.google.android.material.tabs.TabLayout
        android:id="@+id/events_tabs"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_marginTop="40dp"
        app:layout_constraintBottom_toTopOf="@+id/events"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent">

        <com.google.android.material.tabs.TabItem
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="@string/events_tab" />

        <com.google.android.material.tabs.TabItem
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="@string/pending_invites_tab" />

    </com.google.android.material.tabs.TabLayout>

    <androidx.viewpager.widget.ViewPager
        android:id="@+id/events_pager"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:layout_below="@+id/events_tabs">
    </androidx.viewpager.widget.ViewPager>

</androidx.constraintlayout.widget.ConstraintLayout>

既然不支持

FragmentStatePagerAdapter

，那么有没有更好的解决方案来在片段内创建选项卡？

您应该按照弃用通知中的建议，与一起使用

java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.Class java.lang.Object.getClass()' on a null object reference
        at androidx.fragment.app.FragmentTransaction.doAddOp(FragmentTransaction.java:245)
        at androidx.fragment.app.BackStackRecord.doAddOp(BackStackRecord.java:180)
        at androidx.fragment.app.FragmentTransaction.add(FragmentTransaction.java:234)
        at androidx.fragment.app.FragmentPagerAdapter.instantiateItem(FragmentPagerAdapter.java:173)
        at androidx.viewpager.widget.ViewPager.addNewItem(ViewPager.java:1010)
        at androidx.viewpager.widget.ViewPager.populate(ViewPager.java:1224)
        at androidx.viewpager.widget.ViewPager.populate(ViewPager.java:1092)
        at androidx.viewpager.widget.ViewPager.onMeasure(ViewPager.java:1622)
        at android.view.View.measure(View.java:24510)
        at androidx.constraintlayout.widget.ConstraintLayout$Measurer.measure(ConstraintLayout.java:763)
        at androidx.constraintlayout.solver.widgets.analyzer.BasicMeasure.measure(BasicMeasure.java:426)
        at androidx.constraintlayout.solver.widgets.analyzer.BasicMeasure.measureChildren(BasicMeasure.java:105)
        at androidx.constraintlayout.solver.widgets.analyzer.BasicMeasure.solverMeasure(BasicMeasure.java:247)
        at androidx.constraintlayout.solver.widgets.ConstraintWidgetContainer.measure(ConstraintWidgetContainer.java:117)
        at androidx.constraintlayout.widget.ConstraintLayout.resolveSystem(ConstraintLayout.java:1532)
        at androidx.constraintlayout.widget.ConstraintLayout.onMeasure(ConstraintLayout.java:1607)
        at android.view.View.measure(View.java:24510)
        at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:6828)
        at android.widget.FrameLayout.onMeasure(FrameLayout.java:194)
        at android.view.View.measure(View.java:24510)
        at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:6828)
        at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1552)
        at android.widget.LinearLayout.measureHorizontal(LinearLayout.java:1204)
        at android.widget.LinearLayout.onMeasure(LinearLayout.java:723)
        at android.view.View.measure(View.java:24510)
        at androidx.drawerlayout.widget.DrawerLayout.onMeasure(DrawerLayout.java:1156)
        at android.view.View.measure(View.java:24510)
        at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:6828)
        at android.widget.FrameLayout.onMeasure(FrameLayout.java:194)
        at androidx.appcompat.widget.ContentFrameLayout.onMeasure(ContentFrameLayout.java:146)
        at android.view.View.measure(View.java:24510)
        at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:6828)
        at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1552)
        at android.widget.LinearLayout.measureVertical(LinearLayout.java:842)
        at android.widget.LinearLayout.onMeasure(LinearLayout.java:721)
        at android.view.View.measure(View.java:24510)
        at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:6828)
        at android.widget.FrameLayout.onMeasure(FrameLayout.java:194)
        at android.view.View.measure(View.java:24510)
        at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:6828)
        at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1552)
        at android.widget.LinearLayout.measureVertical(LinearLayout.java:842)
        at android.widget.LinearLayout.onMeasure(LinearLayout.java:721)
        at android.view.View.measure(View.java:24510)
        at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:6828)
        at android.widget.FrameLayout.onMeasure(FrameLayout.java:194)
        at com.android.internal.policy.DecorView.onMeasure(DecorView.java:736)
        at android.view.View.measure(View.java:24510)
        at android.view.ViewRootImpl.performMeasure(ViewRootImpl.java:3004)
        at android.view.ViewRootImpl.measureHierarchy(ViewRootImpl.java:1833)
        at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:2122)
        at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:1721)
        at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:7595)
E/AndroidRuntime:     at android.view.Choreographer$CallbackRecord.run(Choreographer.java:966)
        at android.view.Choreographer.doCallbacks(Choreographer.java:790)
        at android.view.Choreographer.doFrame(Choreographer.java:725)
        at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:951)
        at android.os.Handler.handleCallback(Handler.java:883)
        at android.os.Handler.dispatchMessage(Handler.java:100)
        at android.os.Looper.loop(Looper.java:214)
        at android.app.ActivityThread.main(ActivityThread.java:7319)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:492)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:934)