NestedScrollView not listening while scrolling

Question

I'm building an app with Xamarin.Android and when I'm scrolling the listener is not working, it's just being ignored since nothing happens. Why do I need the NestedScrollView? Because I want to hide or show a floating button on scroll:

I have tried to versions:

1. This one is perfectly working in my other view that doesn't contain any ListView:

   view.FindViewById<NestedScrollView>(Resource.Id.nsvMain).ScrollChange += Nsv_ScrollChange;
   private void Nsv_ScrollChange(object sender, NestedScrollView.ScrollChangeEventArgs e)
   {
       if (e.ScrollY > e.OldScrollX)
       {
           FabIdea.Hide();
       }
       else
       {
           FabIdea.Show();
       }
   }
   

2. This is my second idea because the previous one didn't work:

   view.FindViewById<NestedScrollView>(Resource.Id.nsvMain).SetOnScrollChangeListener(new NestedScrollViewListener());
   
   public class NestedScrollViewListener : Java.Lang.Object, IOnScrollChangeListener
   {
       public IntPtr Handle { get; set; }
   
       public void Dispose()
       {
   
       }
   
       public void OnScrollChange(NestedScrollView v, int scrollX, int scrollY, int oldScrollX, int oldScrollY)
       {
           throw new NotImplementedException();
       }
   }
   

This is my XML code:

<?xml version="1.0" encoding="utf-8"?>
<android.support.design.widget.CoordinatorLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent">
    <android.support.v4.widget.NestedScrollView
        android:id="@+id/nsvMain"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:fillViewport="true">
        <LinearLayout
            android:orientation="vertical"
            android:layout_width="match_parent"
            android:layout_height="match_parent">
            <EditText
                  android:id="@+id/txtSearch"
                  android:hint="@string/txtSearch"
                  android:layout_height="wrap_content"
                  android:layout_width="match_parent"
                  android:paddingLeft="10dp"
                  android:paddingRight="10dp" />
            <ListView
                android:nestedScrollingEnabled="true"
                android:divider="@null"
                android:dividerHeight="0dp"
                android:layout_margin="8dp"
                android:layout_width="match_parent"
                android:layout_height="match_parent"
                android:id="@+id/lstRuins" />
        </LinearLayout>
    </android.support.v4.widget.NestedScrollView>
    <android.support.design.widget.FloatingActionButton
        android:id="@+id/fabFilter"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_gravity="bottom|end"
        android:layout_margin="@dimen/fab_margin"
        app:srcCompat="@drawable/filter" />
</android.support.design.widget.CoordinatorLayout>

My only guessing is connected to the ListView, but my App is strictly for API 21+ and I already enabled it as android:nestedScrollingEnabled="true". Also, I'm using this from a Fragment.

I triggered the event of scrolling just for testing purposes from the ViewTreeObserver and I noticed that the ScrollY is always 0:

Answer 1

This is my final implementation, I needed to change the logic in a significant way:

XML:

<?xml version="1.0" encoding="utf-8"?>
<FrameLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:id="@+id/content_frame"
    android:layout_width="match_parent"
    android:layout_height="match_parent">
    <LinearLayout
        android:orientation="vertical"
        android:layout_width="match_parent"
        android:layout_height="match_parent">
        <android.support.design.widget.TextInputLayout
            android:layout_margin="4dp"
            android:id="@+id/txtSearch_layout"
            android:layout_width="match_parent"
            android:layout_height="wrap_content">
          <EditText
            android:drawableStart="@drawable/magnify"
            android:drawableLeft="@drawable/magnify"
            android:id="@+id/txtSearch"
            android:hint="@string/txtSearch"
            android:layout_height="wrap_content"
            android:layout_width="match_parent"
            android:paddingLeft="10dp"
            android:drawablePadding="5dp"
            android:paddingRight="10dp" />
        </android.support.design.widget.TextInputLayout>
        <ListView
            android:divider="@null"
            android:dividerHeight="0dp"
            android:layout_margin="8dp"
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            android:id="@+id/lstRuins" />
    </LinearLayout>

    <android.support.design.widget.FloatingActionButton
        android:id="@+id/fabFilter"
        android:layout_width="wrap_content"
        android:tint="@android:color/white"
        android:layout_height="wrap_content"
        android:layout_gravity="bottom|end"
        android:layout_margin="@dimen/fab_margin"
        app:srcCompat="@drawable/filter" />
</FrameLayout>

I needed to implement a new class that implements: IOnScrollListener

C#:

public class AbsListViewListener : Java.Lang.Object, IOnScrollListener
{
    public MayanListFragment MayanListFragment { get; set; }
    private static int lastItem = 0;

    public AbsListViewListener(MayanListFragment mayanListFragment)
    {
        MayanListFragment = mayanListFragment;
    }

    public void OnScroll(AbsListView view, int firstVisibleItem, int visibleItemCount, int totalItemCount)
    {
        if (MayanListFragment.FabFilter == null)
            return;

        if (lastItem > (firstVisibleItem + visibleItemCount) || firstVisibleItem == 0)
        {
            MayanListFragment.FabFilter.Show();
        }
        else
        {
            MayanListFragment.FabFilter.Hide();
        }
        lastItem = firstVisibleItem + visibleItemCount;
    }

    public void OnScrollStateChanged(AbsListView view, [GeneratedEnum] ScrollState scrollState)
    {

    }
}


LstRuins.SetOnScrollListener(new AbsListViewListener(this));

And then it generally works.