Going down the BottomSheetBehavior rabbit hole...

BottomSheetBehavior only supports one scrolling child. Add support for a ViewPager.
ViewPager.getChildAt sometimes does not match the actual position.
Make sure that it keeps all children using setOffscreenPageLimit

5 files changed, 99 insertions, 19 deletions

diff --git a/app/src/main/java/com/google/android/material/bottomsheet/ViewPagerBottomSheetBehavior.java b/app/src/main/java/com/google/android/material/bottomsheet/ViewPagerBottomSheetBehavior.java
new file mode 100644
index 000000000..2d211704d
--- /dev/null
+++ b/app/src/main/java/com/google/android/material/bottomsheet/ViewPagerBottomSheetBehavior.java
@@ -0,0 +1,75 @@
+package com.google.android.material.bottomsheet;
+
+import android.content.Context;
+import android.util.AttributeSet;
+import android.view.View;
+import android.view.ViewGroup;
+import androidx.coordinatorlayout.widget.CoordinatorLayout;
+import androidx.core.view.ViewCompat;
+import androidx.viewpager.widget.ViewPager;
+
+import java.lang.ref.WeakReference;
+
+/**
+ * Override {@link #findScrollingChild(View)} to support {@link ViewPager}'s nested scrolling.
+ * By the way, In order to override package level method and field.
+ * This class put in the same package path where {@link BottomSheetBehavior} located.
+ * Source: https://medium.com/@hanru.yeh/funny-solution-that-makes-bottomsheetdialog-support-viewpager-with-nestedscrollingchilds-bfdca72235c3
+ */
+public class ViewPagerBottomSheetBehavior<V extends View> extends BottomSheetBehavior<V> {
+
+    public ViewPagerBottomSheetBehavior() {
+        super();
+    }
+
+    public ViewPagerBottomSheetBehavior(Context context, AttributeSet attrs) {
+        super(context, attrs);
+    }
+
+    @Override
+    View findScrollingChild(View view) {
+        if (ViewCompat.isNestedScrollingEnabled(view)) {
+            return view;
+        }
+
+        if (view instanceof ViewPager) {
+            ViewPager viewPager = (ViewPager) view;
+            View currentViewPagerChild = viewPager.getChildAt(viewPager.getCurrentItem());
+            return findScrollingChild(currentViewPagerChild);
+        } else if (view instanceof ViewGroup) {
+            ViewGroup group = (ViewGroup) view;
+            for (int i = 0, count = group.getChildCount(); i < count; i++) {
+                View scrollingChild = findScrollingChild(group.getChildAt(i));
+                if (scrollingChild != null) {
+                    return scrollingChild;
+                }
+            }
+        }
+        return null;
+    }
+
+    public void updateScrollingChild() {
+        final View scrollingChild = findScrollingChild(viewRef.get());
+        nestedScrollingChildRef = new WeakReference<>(scrollingChild);
+    }
+
+    /**
+     * A utility function to get the {@link ViewPagerBottomSheetBehavior} associated with the {@code view}.
+     *
+     * @param view The {@link View} with {@link ViewPagerBottomSheetBehavior}.
+     * @return The {@link ViewPagerBottomSheetBehavior} associated with the {@code view}.
+     */
+    @SuppressWarnings("unchecked")
+    public static <V extends View> ViewPagerBottomSheetBehavior<V> from(V view) {
+        ViewGroup.LayoutParams params = view.getLayoutParams();
+        if (!(params instanceof CoordinatorLayout.LayoutParams)) {
+            throw new IllegalArgumentException("The view is not a child of CoordinatorLayout");
+        }
+        CoordinatorLayout.Behavior behavior = ((CoordinatorLayout.LayoutParams) params).getBehavior();
+        if (!(behavior instanceof ViewPagerBottomSheetBehavior)) {
+            throw new IllegalArgumentException(
+                    "The view is not associated with ViewPagerBottomSheetBehavior");
+        }
+        return (ViewPagerBottomSheetBehavior<V>) behavior;
+    }
+}
\ No newline at end of file
diff --git a/app/src/main/java/de/danoeh/antennapod/adapter/ChaptersListAdapter.java b/app/src/main/java/de/danoeh/antennapod/adapter/ChaptersListAdapter.java
index 8b0aa537e..cb72a9150 100644
--- a/app/src/main/java/de/danoeh/antennapod/adapter/ChaptersListAdapter.java
+++ b/app/src/main/java/de/danoeh/antennapod/adapter/ChaptersListAdapter.java
@@ -2,7 +2,6 @@ package de.danoeh.antennapod.adapter;
 
 import android.content.Context;
 import android.text.TextUtils;
-import android.util.Log;
 import android.view.LayoutInflater;
 import android.view.View;
 import android.view.ViewGroup;
@@ -116,7 +115,6 @@ public class ChaptersListAdapter extends RecyclerView.Adapter<ChaptersListAdapte
     @Override
     public int getItemCount() {
         if (media == null || media.getChapters() == null) {
-            Log.d("aaaaa", "0");
             return 0;
         }
         // ignore invalid chapters
@@ -126,7 +124,6 @@ public class ChaptersListAdapter extends RecyclerView.Adapter<ChaptersListAdapte
                 counter++;
             }
         }
-        Log.d("aaaaa", "0"+counter);
         return counter;
     }
 
diff --git a/app/src/main/java/de/danoeh/antennapod/fragment/AudioPlayerFragment.java b/app/src/main/java/de/danoeh/antennapod/fragment/AudioPlayerFragment.java
index d1c073cac..3be79a094 100644
--- a/app/src/main/java/de/danoeh/antennapod/fragment/AudioPlayerFragment.java
+++ b/app/src/main/java/de/danoeh/antennapod/fragment/AudioPlayerFragment.java
@@ -16,7 +16,7 @@ import androidx.annotation.Nullable;
 import androidx.appcompat.widget.Toolbar;
 import androidx.fragment.app.Fragment;
 import androidx.fragment.app.FragmentManager;
-import androidx.fragment.app.FragmentStatePagerAdapter;
+import androidx.fragment.app.FragmentPagerAdapter;
 import androidx.viewpager.widget.ViewPager;
 import com.google.android.material.bottomsheet.BottomSheetBehavior;
 import de.danoeh.antennapod.R;
@@ -119,6 +119,14 @@ public class AudioPlayerFragment extends Fragment implements
         pager = root.findViewById(R.id.pager);
         AudioPlayerPagerAdapter pagerAdapter = new AudioPlayerPagerAdapter(getFragmentManager());
         pager.setAdapter(pagerAdapter);
+        // Required for getChildAt(int) in ViewPagerBottomSheetBehavior to return the correct page
+        pager.setOffscreenPageLimit(NUM_CONTENT_FRAGMENTS);
+        pager.addOnPageChangeListener(new ViewPager.SimpleOnPageChangeListener() {
+            @Override
+            public void onPageSelected(int position) {
+                pager.post(() -> ((MainActivity) getActivity()).getBottomSheet().updateScrollingChild());
+            }
+        });
         pageIndicator = root.findViewById(R.id.page_indicator);
         pageIndicator.setViewPager(pager);
         pageIndicator.setOnClickListener(v ->
@@ -468,7 +476,7 @@ public class AudioPlayerFragment extends Fragment implements
         return false;
     }
 
-    private static class AudioPlayerPagerAdapter extends FragmentStatePagerAdapter {
+    private static class AudioPlayerPagerAdapter extends FragmentPagerAdapter {
         private static final String TAG = "AudioPlayerPagerAdapter";
 
         public AudioPlayerPagerAdapter(FragmentManager fm) {
diff --git a/app/src/main/java/de/danoeh/antennapod/fragment/ItemDescriptionFragment.java b/app/src/main/java/de/danoeh/antennapod/fragment/ItemDescriptionFragment.java
index 256615199..58cc9290c 100644
--- a/app/src/main/java/de/danoeh/antennapod/fragment/ItemDescriptionFragment.java
+++ b/app/src/main/java/de/danoeh/antennapod/fragment/ItemDescriptionFragment.java
@@ -10,6 +10,7 @@ import android.view.View;
 import android.view.ViewGroup;
 import androidx.annotation.NonNull;
 import androidx.fragment.app.Fragment;
+import de.danoeh.antennapod.R;
 import de.danoeh.antennapod.core.util.playback.PlaybackController;
 import de.danoeh.antennapod.core.util.playback.Timeline;
 import de.danoeh.antennapod.view.ShownotesWebView;
@@ -35,7 +36,8 @@ public class ItemDescriptionFragment extends Fragment {
     @Override
     public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
         Log.d(TAG, "Creating view");
-        webvDescription = new ShownotesWebView(getActivity().getApplicationContext());
+        View root = inflater.inflate(R.layout.item_description_fragment, container, false);
+        webvDescription = root.findViewById(R.id.webview);
         webvDescription.setTimecodeSelectedListener(time -> {
             if (controller != null) {
                 controller.seekTo(time);
@@ -46,7 +48,7 @@ public class ItemDescriptionFragment extends Fragment {
             webvDescription.postDelayed(ItemDescriptionFragment.this::restoreFromPreference, 50);
         });
         registerForContextMenu(webvDescription);
-        return webvDescription;
+        return root;
     }
 
     @Override
diff --git a/app/src/main/java/de/danoeh/antennapod/view/LockableBottomSheetBehavior.java b/app/src/main/java/de/danoeh/antennapod/view/LockableBottomSheetBehavior.java
index f4c073fc6..8e8d98fc9 100644
--- a/app/src/main/java/de/danoeh/antennapod/view/LockableBottomSheetBehavior.java
+++ b/app/src/main/java/de/danoeh/antennapod/view/LockableBottomSheetBehavior.java
@@ -5,14 +5,13 @@ import android.util.AttributeSet;
 import android.view.MotionEvent;
 import android.view.View;
 import androidx.coordinatorlayout.widget.CoordinatorLayout;
-import com.google.android.material.bottomsheet.BottomSheetBehavior;
+import com.google.android.material.bottomsheet.ViewPagerBottomSheetBehavior;
 
 /**
  * Based on https://stackoverflow.com/a/40798214
  */
-public class LockableBottomSheetBehavior<V extends View> extends BottomSheetBehavior<V> {
-
-    private boolean mLocked = false;
+public class LockableBottomSheetBehavior<V extends View> extends ViewPagerBottomSheetBehavior<V> {
+    private boolean isLocked = false;
 
     public LockableBottomSheetBehavior() {}
 
@@ -21,14 +20,14 @@ public class LockableBottomSheetBehavior<V extends View> extends BottomSheetBeha
     }
 
     public void setLocked(boolean locked) {
-        mLocked = locked;
+        isLocked = locked;
     }
 
     @Override
     public boolean onInterceptTouchEvent(CoordinatorLayout parent, V child, MotionEvent event) {
         boolean handled = false;
 
-        if (!mLocked) {
+        if (!isLocked) {
             handled = super.onInterceptTouchEvent(parent, child, event);
         }
 
@@ -39,7 +38,7 @@ public class LockableBottomSheetBehavior<V extends View> extends BottomSheetBeha
     public boolean onTouchEvent(CoordinatorLayout parent, V child, MotionEvent event) {
         boolean handled = false;
 
-        if (!mLocked) {
+        if (!isLocked) {
             handled = super.onTouchEvent(parent, child, event);
         }
 
@@ -51,7 +50,7 @@ public class LockableBottomSheetBehavior<V extends View> extends BottomSheetBeha
                                        View target, int nestedScrollAxes) {
         boolean handled = false;
 
-        if (!mLocked) {
+        if (!isLocked) {
             handled = super.onStartNestedScroll(coordinatorLayout, child, directTargetChild, target, nestedScrollAxes);
         }
 
@@ -61,14 +60,14 @@ public class LockableBottomSheetBehavior<V extends View> extends BottomSheetBeha
     @Override
     public void onNestedPreScroll(CoordinatorLayout coordinatorLayout, V child, View target,
                                   int dx, int dy, int[] consumed) {
-        if (!mLocked) {
+        if (!isLocked) {
             super.onNestedPreScroll(coordinatorLayout, child, target, dx, dy, consumed);
         }
     }
 
     @Override
     public void onStopNestedScroll(CoordinatorLayout coordinatorLayout, V child, View target) {
-        if (!mLocked) {
+        if (!isLocked) {
             super.onStopNestedScroll(coordinatorLayout, child, target);
         }
     }
@@ -78,11 +77,10 @@ public class LockableBottomSheetBehavior<V extends View> extends BottomSheetBeha
                                     float velocityX, float velocityY) {
         boolean handled = false;
 
-        if (!mLocked) {
+        if (!isLocked) {
             handled = super.onNestedPreFling(coordinatorLayout, child, target, velocityX, velocityY);
         }
 
         return handled;
-
     }
 }