How do I deactivate scrolling the parent scrollview if the nestedscrollview ends?

Question

I have a nestedscrollview inside a scrollview and it is working, but I do not want the behavior that if I scroll inside the nestedscrollview and I reach either the top or the bottom, that automatically the scroll keeps on going with the "parent" scrollview. I find that absolutely annoying.

New App Project with basic activity and this content of content_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"
        app:layout_behavior="@string/appbar_scrolling_view_behavior"
        tools:showIn="@layout/activity_main"
        tools:context=".MainActivity">
    <LinearLayout
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            android:orientation="vertical"
            android:layout_margin="5dp"
            android:background="@color/colorPrimary">

        <TextView
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:text="Root"
                app:layout_constraintBottom_toBottomOf="parent"
                app:layout_constraintLeft_toLeftOf="parent"
                app:layout_constraintRight_toRightOf="parent"
                app:layout_constraintTop_toTopOf="parent"
                android:layout_margin="5dp"
                android:background="@color/colorAccent"/>

        <ScrollView
                android:id="@+id/scrollViewRoot"
                android:layout_width="match_parent"
                android:layout_height="match_parent"
                android:background="@android:color/holo_orange_dark"
                android:paddingRight="40dp">
            <LinearLayout
                    android:layout_width="match_parent"
                    android:layout_height="match_parent"
                    android:orientation="vertical"
                    android:layout_margin="5dp"
                    android:background="@color/colorPrimary">

                <TextView
                        android:text="Nested1"
                        android:layout_width="match_parent"
                        android:layout_height="wrap_content" android:id="@+id/textViewNested1"
                        android:layout_margin="5dp"
                        android:background="@color/colorAccent"/>
                <androidx.core.widget.NestedScrollView
                        android:layout_width="match_parent"
                        android:layout_height="1000dp" android:fillViewport="true"
                        android:background="@android:color/black">
                    <LinearLayout android:layout_width="match_parent"
                                  android:layout_height="2000dp"
                                  android:orientation="vertical"
                                  android:layout_margin="5dp"
                                  android:background="@color/colorPrimaryDark">
                        <TextView
                                android:text="TextView"
                                android:layout_width="match_parent"
                                android:layout_height="1800dp" android:id="@+id/textView3"
                                android:layout_margin="5dp"
                                android:background="@color/colorAccent"
                        />
                    </LinearLayout>
                </androidx.core.widget.NestedScrollView>
                <TextView
                        android:text="Nested2"
                        android:layout_width="match_parent"
                        android:layout_height="wrap_content" android:id="@+id/textViewNested2"
                        android:layout_margin="5dp"
                        android:background="@color/colorAccent"
                />
                <androidx.core.widget.NestedScrollView
                        android:layout_width="match_parent"
                        android:layout_height="1000dp" android:fillViewport="true"

                        android:background="@android:color/black">
                    <LinearLayout android:layout_width="match_parent"
                                  android:layout_height="2000dp"
                                  android:orientation="vertical"
                                  android:layout_margin="5dp"
                                  android:background="@color/colorPrimaryDark">
                        <TextView
                                android:text="TextView"
                                android:layout_width="match_parent"
                                android:layout_height="1800dp" android:id="@+id/textView4"
                                android:layout_margin="5dp"
                                android:background="@color/colorAccent"
                        />
                    </LinearLayout>
                </androidx.core.widget.NestedScrollView>

            </LinearLayout>

        </ScrollView>

    </LinearLayout>

</androidx.constraintlayout.widget.ConstraintLayout>

WRONG: scrolling inside nested can scroll the parent scrollview if top or bottom is reached.

RIGHT: scrolling inside nested can NOT scroll the parent scrollview even if top or bottom is reached

Answer 1

Out of the box, I believe this is not possible. However, you can create your own subclass of NestedScrollView and override onNestedScroll() and onNestedFling() to prevent the passing of "unconsumed" scroll values.

class MyNestedScrollView(context: Context, attrs: AttributeSet?) : NestedScrollView(context, attrs) {

    override fun onNestedScroll(target: View, dxConsumed: Int, dyConsumed: Int, dxUnconsumed: Int, dyUnconsumed: Int, type: Int) {
        super.onNestedScroll(target, dxConsumed, dyConsumed, 0, 0, type)
    }

    override fun onNestedFling(target: View, velocityX: Float, velocityY: Float, consumed: Boolean): Boolean {
        return super.onNestedFling(target, velocityX, velocityY, true)
    }
}

In onNestedScroll() we're intercepting dxUnconsumed and dyUnconsumed and re-writing them to 0. In onNestedFling() we're intercepting consumed and re-writing it to true.

This makes the system think that the child has always consumed all of the scrolling, so the parent never scrolls in response to a child scroll that hits the boundaries.

Now we just have to use this as the outer scrollview in our layout:

<?xml version="1.0" encoding="utf-8"?>
<com.example.stackoverflow.MyNestedScrollView
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:orientation="vertical">

        <!-- ... -->

        <android.support.v4.widget.NestedScrollView
            android:layout_width="match_parent"
            android:layout_height="your height here">

            <!-- ... -->

        </android.support.v4.widget.NestedScrollView>

        <!-- ... -->

    </LinearLayout>

</com.example.playground.MyNestedScrollView>