AppBarShadowDependency

appbargrad.xml

<?xml version="1.0" encoding="utf-8"?>
<shape xmlns:android="http://schemas.android.com/apk/res/android">
    <gradient android:startColor="#34000000"
              android:endColor="#00000000"
              android:angle="-90"
              android:useLevel="false"
              android:type="linear"/>
</shape>

fragment_main.xml

<?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"
              xmlns:app="http://schemas.android.com/apk/res-auto"
              android:layout_width="match_parent"
              android:layout_height="match_parent"
              android:orientation="vertical">


    <androidx.core.widget.NestedScrollView
            android:layout_width="match_parent"
            android:layout_marginBottom="3dp"
            app:layout_constraintTop_toBottomOf="@id/custombar"
            android:layout_height="wrap_content"
            android:id="@+id/scrollview"
            app:layout_constraintStart_toStartOf="parent"
            app:layout_constraintHorizontal_bias="0.5"
            app:layout_constraintEnd_toEndOf="parent" android:background="@color/colorPrimary">

        <FrameLayout android:layout_width="match_parent"
                     android:layout_height="wrap_content">

            <TextView android:layout_width="match_parent" android:layout_height="wrap_content"
            android:text="@string/large_text"/>

        </FrameLayout>

    </androidx.core.widget.NestedScrollView>
    <ImageView
            android:layout_width="match_parent"
            android:background="@drawable/appbargrad"
            app:layout_constraintTop_toBottomOf="@id/custombar"
            android:layout_height="3dp" android:id="@+id/barshadow"
    />
    <LinearLayout android:layout_width="match_parent"
                  android:layout_height="wrap_content"
                  app:layout_constraintTop_toTopOf="parent"
                  android:orientation="vertical" android:background="@color/colorPrimary"
                  android:id="@+id/custombar" app:layout_constraintStart_toStartOf="parent"
                  app:layout_constraintHorizontal_bias="0.5" app:layout_constraintEnd_toEndOf="parent">
        <TextView
                android:text="TextView"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content" android:id="@+id/textView6"
                tools:layout_editor_absoluteX="191dp" app:layout_constraintStart_toStartOf="parent"
                app:layout_constraintHorizontal_bias="0.5" app:layout_constraintEnd_toEndOf="parent"
                app:layout_constraintTop_toTopOf="parent"/>
        <TextView
                android:text="TextView"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content" android:id="@+id/textView5"
                tools:layout_editor_absoluteX="191dp" app:layout_constraintStart_toStartOf="parent"
                app:layout_constraintHorizontal_bias="0.5" app:layout_constraintEnd_toEndOf="parent"
                app:layout_constraintTop_toTopOf="parent"/>
        <TextView
                android:text="TextView"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content" android:id="@+id/textView4"
                tools:layout_editor_absoluteX="191dp" app:layout_constraintStart_toStartOf="parent"
                app:layout_constraintHorizontal_bias="0.5" app:layout_constraintEnd_toEndOf="parent"
                app:layout_constraintTop_toTopOf="parent"/>


    </LinearLayout>




</androidx.constraintlayout.widget.ConstraintLayout>

main_activity.kt

scrollview.setOnScrollChangeListener { v: NestedScrollView?, scrollX: Int, scrollY: Int, oldScrollX: Int, oldScrollY: Int ->
            barshadow.alpha = (scrollY/50f)
        }