Android ViewPager with RecyclerView works incorrectly inside BottomSheet

Question

When I try to scroll list, sometimes this works incorrect - BottomSheet intercepts the scroll event and hides.

How to reproduce this:

1. Open Bottom Sheet

Answer 1

There is another approach that does not require modifying BottomSheetBehavior but instead leverages the fact that the BottomSheetBehavior only recognizes the first NestedScrollView with NestedScrollingEnabled it finds. So instead of altering this logic inside BottomSheetBehavior, enable and disable the appropriate scroll views. I discovered this approach here: https://imnotyourson.com/cannot-scroll-scrollable-content-inside-viewpager-as-bottomsheet-of-coordinatorlayout/

In my case my BottomSheetBehavior was using a TabLayout with a FragmentPagerAdapter so my FragmentPagerAdapter needed the following code:

@Override
public void setPrimaryItem(@NonNull ViewGroup container, int position, @NonNull Object object) {

        super.setPrimaryItem(container, position, object);

        Fragment f = ((Fragment)object);
        String activeFragmentTag = f.getTag();
        View view = f.getView();

        if (view != null) {
            View nestedView = view.findViewWithTag("nested");               
            if ( nestedView != null && nestedView instanceof NestedScrollView) {
                ((NestedScrollView)nestedView).setNestedScrollingEnabled(true);
            }
        }

        FragmentManager fm = f.getFragmentManager();

        for(Fragment frag : fm.getFragments()) {

            if (frag.getTag() != activeFragmentTag) {
                View v = frag.getView();
                if (v!= null) {

                    View nestedView = v.findViewWithTag("nested");

                    if (nestedView!= null && nestedView instanceof NestedScrollView) {
                        ((NestedScrollView)nestedView).setNestedScrollingEnabled(false);
                    }
                }
            }
        }

        container.requestLayout();
    }

Any nested scroll views in your fragments just need to have the "nested" tag.

Here is a sample Fragment layout file:

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout
    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"
    tools:context=".ui.MLeftFragment">

    <androidx.core.widget.NestedScrollView
        android:id="@+id/nestedScrollView"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:tag="nested"
        android:fillViewport="true">

        <LinearLayout
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            android:orientation="vertical">

            <!-- TODO: Update blank fragment layout -->
            <TextView
                android:layout_width="match_parent"
                android:layout_height="wrap_content"
                android:text="@string/hello_mool_left_fragment" />      

        </LinearLayout>  

    </androidx.core.widget.NestedScrollView>

</androidx.constraintlayout.widget.ConstraintLayout>