ViewPagerBottomSheetBehavior overrides package level methods and fields

ViewPagerBottomSheetBehavior.java

package android.support.design.widget;

import android.support.v4.view.ViewCompat;
import android.support.v4.view.ViewPager;
import android.view.View;
import android.view.ViewGroup;

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.
 */
public class ViewPagerBottomSheetBehavior<V extends View> extends BottomSheetBehavior<V> {

    @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());
            View scrollingChild = findScrollingChild(currentViewPagerChild);
            if (scrollingChild != null) {
                return scrollingChild;
            }
        } 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(mViewRef.get());
        mNestedScrollingChildRef = 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;
    }
}

from medium post, nice work!👍