Revert ViewPager2 use in ItemPagerFragment

Because of "accidentally switch to another page when trying to scroll up/down"
#4020 (comment)

Will revert this once we reached to a solution for it.

app/src/main/java/de/danoeh/antennapod/fragment/ItemPagerFragment.java

@@ -7,30 +7,29 @@
 import android.view.MenuItem;
 import android.view.View;
 import android.view.ViewGroup;
-
 import androidx.annotation.NonNull;
 import androidx.annotation.Nullable;
 import androidx.appcompat.app.AppCompatActivity;
 import androidx.appcompat.widget.Toolbar;
 import androidx.core.view.ViewCompat;
 import androidx.fragment.app.Fragment;
-import androidx.viewpager2.adapter.FragmentStateAdapter;
-import androidx.viewpager2.widget.ViewPager2;
-
-import org.greenrobot.eventbus.EventBus;
-import org.greenrobot.eventbus.Subscribe;
-import org.greenrobot.eventbus.ThreadMode;
-
+import androidx.fragment.app.FragmentStatePagerAdapter;
+import androidx.viewpager.widget.ViewPager;
 import de.danoeh.antennapod.R;
+import de.danoeh.antennapod.activity.CastEnabledActivity;
 import de.danoeh.antennapod.activity.MainActivity;
 import de.danoeh.antennapod.core.event.FeedItemEvent;
 import de.danoeh.antennapod.core.feed.FeedItem;
 import de.danoeh.antennapod.core.storage.DBReader;
+import de.danoeh.antennapod.core.util.Flavors;
 import de.danoeh.antennapod.menuhandler.FeedItemMenuHandler;
 import io.reactivex.Observable;
 import io.reactivex.android.schedulers.AndroidSchedulers;
 import io.reactivex.disposables.Disposable;
 import io.reactivex.schedulers.Schedulers;
+import org.greenrobot.eventbus.EventBus;
+import org.greenrobot.eventbus.Subscribe;
+import org.greenrobot.eventbus.ThreadMode;
 
 /**
  * Displays information about a list of FeedItems.
@@ -42,7 +41,7 @@ public class ItemPagerFragment extends Fragment {
     /**
      * Creates a new instance of an ItemPagerFragment.
      *
-     * @param feeditems   The IDs of the FeedItems that belong to the same list
+     * @param feeditems The IDs of the FeedItems that belong to the same list
      * @param feedItemPos The position of the FeedItem that is currently shown
      * @return The ItemFragment instance
      */
@@ -77,21 +76,31 @@ public View onCreateView(@NonNull LayoutInflater inflater, @Nullable ViewGroup c
         feedItems = getArguments().getLongArray(ARG_FEEDITEMS);
         int feedItemPos = getArguments().getInt(ARG_FEEDITEM_POS);
 
-        ViewPager2 pager = layout.findViewById(R.id.pager);
+        ViewPager pager = layout.findViewById(R.id.pager);
         // FragmentStatePagerAdapter documentation:
         // > When using FragmentStatePagerAdapter the host ViewPager must have a valid ID set.
         // When opening multiple ItemPagerFragments by clicking "item" -> "visit podcast" -> "item" -> etc,
         // the ID is no longer unique and FragmentStatePagerAdapter does not display any pages.
         int newId = ViewCompat.generateViewId();
         pager.setId(newId);
-        pager.setAdapter(new ItemPagerAdapter(this));
-        pager.setCurrentItem(feedItemPos, false);
+        pager.setAdapter(new ItemPagerAdapter());
+        pager.setCurrentItem(feedItemPos);
         loadItem(feedItems[feedItemPos]);
-        pager.registerOnPageChangeCallback(new ViewPager2.OnPageChangeCallback() {
+        pager.addOnPageChangeListener(new ViewPager.OnPageChangeListener() {
+            @Override
+            public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {
+
+            }
+
             @Override
             public void onPageSelected(int position) {
                 loadItem(feedItems[position]);
             }
+
+            @Override
+            public void onPageScrollStateChanged(int state) {
+
+            }
         });
 
         EventBus.getDefault().register(this);
@@ -164,20 +173,20 @@ private void openPodcast() {
         ((MainActivity) getActivity()).loadChildFragment(fragment);
     }
 
-    private class ItemPagerAdapter extends FragmentStateAdapter {
+    private class ItemPagerAdapter extends FragmentStatePagerAdapter {
 
-        ItemPagerAdapter(@NonNull Fragment fragment) {
-            super(fragment);
+        ItemPagerAdapter() {
+            super(getFragmentManager(), BEHAVIOR_RESUME_ONLY_CURRENT_FRAGMENT);
         }
 
         @NonNull
         @Override
-        public Fragment createFragment(int position) {
+        public Fragment getItem(int position) {
             return ItemFragment.newInstance(feedItems[position]);
         }
 
         @Override
-        public int getItemCount() {
+        public int getCount() {
             return feedItems.length;
         }
     }

app/src/main/res/layout/feeditem_fragment.xml

@@ -171,18 +171,12 @@
 
     </LinearLayout>
 
-    <de.danoeh.antennapod.view.NestedScrollableHost
-        android:layout_below="@id/header"
+    <de.danoeh.antennapod.view.ShownotesWebView
+        android:id="@+id/webvDescription"
         android:layout_width="match_parent"
-        android:layout_height="match_parent">
-
-        <de.danoeh.antennapod.view.ShownotesWebView
-            android:id="@+id/webvDescription"
-            android:layout_width="match_parent"
-            android:layout_height="match_parent"
-            android:foreground="?android:windowContentOverlay" />
-
-    </de.danoeh.antennapod.view.NestedScrollableHost>
+        android:layout_below="@id/header"
+        android:layout_height="match_parent"
+        android:foreground="?android:windowContentOverlay" />
 
     <FrameLayout
         android:layout_width="match_parent"

app/src/main/res/layout/feeditem_pager_fragment.xml

@@ -14,7 +14,7 @@
             app:navigationIcon="?homeAsUpIndicator"
             android:id="@+id/toolbar"/>
 
-    <androidx.viewpager2.widget.ViewPager2
+    <androidx.viewpager.widget.ViewPager
             android:id="@+id/pager"
             android:layout_width="match_parent"
             android:layout_height="match_parent"/>