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

I have the solution for AndroidX, Kotlin. Tested and working on 'com.google.android.material:material:1.1.0-alpha06'.

I also used this: MEDIUM BLOG as a guide.

Here is My ViewPagerBottomSheetBehavior Kotlin Class:

package com.google.android.material.bottomsheet
import android.content.Context
import android.util.AttributeSet
import android.view.View
import androidx.annotation.VisibleForTesting
import androidx.viewpager.widget.ViewPager
import java.lang.ref.WeakReference
class ViewPagerBottomSheetBehavior
    : com.google.android.material.bottomsheet.BottomSheetBehavior,
    ViewPager.OnPageChangeListener {

    constructor() : super()
    constructor(context: Context, attrs: AttributeSet) : super(context, attrs)

    override fun onPageScrollStateChanged(state: Int) {}
    override fun onPageScrolled(position: Int, positionOffset: Float, positionOffsetPixels: Int) {}
    override fun onPageSelected(position: Int) {
        val container = viewRef?.get() ?: return
        nestedScrollingChildRef = WeakReference(findScrollingChild(container))
    }

    @VisibleForTesting
    override fun findScrollingChild(view: View?): View? {
        return if (view is ViewPager) {
            view.focusedChild?.let { findScrollingChild(it) }
        } else {
            super.findScrollingChild(view)
        }
    }
}

The final solutios was adding the super constructors in the Class:

constructor() : super()
constructor(context: Context, attrs: AttributeSet) : super(context, attrs)

Remember, you have to add ViewPagerBottomSheetBehavior Kotlin Class in the next path: Path Class Image reference because, you must override a private method>

@VisibleForTesting
override fun findScrollingChild(view: View?): View? {
    return if (view is ViewPager) {
        view.focusedChild?.let { findScrollingChild(it) }
    } else {
        super.findScrollingChild(view)
    }
}

After that, you can use it as a View attribute, like this>