BottomNavigationView does not hide on scrolling inside fragment, if fragment contains AppBarLayout

Question

I'm having a lot of problems with scrolling and detection of it inside fragments using coordinatorLayout in Android. I have a "MainActivity" that contains 3 fragments. In one of those fragments I have an Appbar that collapses when fragment is scrolled. I've managed to do that, but if I set scrolling behavior to allow that, my bottomNavigationView (which is found in mainactivity.xml) does NOT react to scrolling. Codes go something like this:

Fragment1.xml

<android.support.design.widget.CoordinatorLayout
...
...>
    <android.support.design.widget.AppBarLayout
 ...
 ...>
        <android.support.design.widget.CollapsingToolbarLayout
                 app:layout_scrollFlags="scroll|exitUntilCollapsed"
   ...>
            <android.support.v7.widget.Toolbar
     .../>
        </android.support.design.widget.CollapsingToolbarLayout>
    </android.support.design.widget.AppBarLayout>

   <android.support.v4.widget.NestedScrollView
        app:layout_behavior="@string/appbar_scrolling_view_behavior">
   </android.support.v4.widget.NestedScrollView>

</android.support.design.widget.CoordinatorLayout>

MainActivity.xml

<android.support.design.widget.CoordinatorLayout
.../>
    <FrameLayout
        app:layout_behavior="@string/appbar_scrolling_view_behavior"
 .../>
    <android.support.design.widget.BottomNavigationView
      app:layout_behavior="@string/hide_bottom_view_on_scroll_behavior"
.../>
</android.support.design.widget.CoordinatorLayout>

Now, this works well enough, in the sense that when I scroll inside fragment my AppBar collapses into the title (which is what I want), BUT my bottomNavigationView does not react to scrolling.

What I found out is that if i add the line

app:layout_behavior="@string/appbar_scrolling_view_behavior"

to the AppBarLayout xml declaration I get the bottomView to collapse on scroll event (when I scroll up it shows again). So basically either I have the ability to collapse appbar inside fragment OR I have the ability to hide BottomNavigationView when I detect a scroll event inside the fragment.

Any sort of help would be appreciated.

Answer 1

In order to hide bottom navigation in reaction to scrolling inside the fragement modify onCreateView method on fragment1.kt as follows

override fun onCreateView(
        inflater: LayoutInflater, container: ViewGroup?,
        savedInstanceState: Bundle?
    ): View? {

        ...

        // access the bottom nav which is on the main activity
        val bottomNav: BottomNavigationView = activity!!.findViewById(R.id.bottom_nav)

        // hide bottom nav when scrolling
        rvList.addOnScrollListener(object : RecyclerView.OnScrollListener() {

            override fun onScrolled(recyclerView: RecyclerView, dx: Int, dy: Int) {
                if (dy > 0 || dy < 0) {
                    bottomNav.visibility = View.GONE
                }
            }

            override fun onScrollStateChanged(recyclerView: RecyclerView, newState: Int) {
                if (newState == RecyclerView.SCROLL_STATE_IDLE) {
                    bottomNav.visibility = View.VISIBLE
                }

                super.onScrollStateChanged(recyclerView, newState)
            }
        })

        return view
}

---

In Java

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
        Bundle savedInstanceState) {
        ...

    // access the bottom nav which is on the main activity
    BottomNavigationView bottomNav = getActivity.findViewById(R.id.bottom_nav);

    // hide bottom nav when scrolling
    recyclerView.addOnScrollListener(new RecyclerView.OnScrollListener()
    {
        @Override
        public void onScrolled(RecyclerView recyclerView, int dx, int dy)
        {
             if (dy > 0 ||dy<0)
             {
                 bottomNav.setVisibility(View.GONE);
             }
        }

        @Override
        public void onScrollStateChanged(RecyclerView recyclerView, int newState)
        {
             if (newState == RecyclerView.SCROLL_STATE_IDLE)
             {
                  bottomNav.setVisibility(View.VISIBLE);
             }

             super.onScrollStateChanged(recyclerView, newState);
        }
    });

        return view;
 }

---

Update:

Extract the listener code to a separate function as given below (in Kotlin)

   public fun hideBottomNav(
        rvList: RecyclerView,
        bottomNav: BottomNavigationView
    ) {
        rvList.addOnScrollListener(object : RecyclerView.OnScrollListener() {

            override fun onScrolled(recyclerView: RecyclerView, dx: Int, dy: Int) {
                if (dy > 0 || dy < 0) {
                    bottomNav.visibility = View.GONE
                }
            }

            override fun onScrollStateChanged(recyclerView: RecyclerView, newState: Int) {
                if (newState == RecyclerView.SCROLL_STATE_IDLE) {
                    bottomNav.visibility = View.VISIBLE
                }

                super.onScrollStateChanged(recyclerView, newState)
            }
        })
    }