Android UI – dynamic button alignment change

I have following xml

<ConstraintLayout>
    <NestedScrollView>
        <ConstraintLayout>
            <RecycleView/>
        </ConstraintLayout>
    </NestedScrollView>
    <Button BottomTo_BottomOf = parent/>
</ConstraintLayout>

When I load the screen that I want the button to be stick at the screen bottom.
I am loading some elements dynamically (based on user action) in the recycleview and once the recycleview has elements more then the screen size then I want the button alignment to be changed from screen bottom to the end of the content and visible once user scroll through all the contents

You need to add below tag to the button –

 app:layout_constraintBottom_toBottomOf="parent"

Add these attribute to Button:

    app:layout_constraintStart_toStartOf="parent"
    app:layout_constraintEnd_toEndOf="parent"
    app:layout_constraintBottom_toBottomOf="parent"

Add these attribute to NestedScrollView

    android:layout_width="match_parent"
    android:layout_height="0dp"
    app:layout_constraintStart_toStartOf="parent"
    app:layout_constraintEnd_toEndOf="parent"
    app:layout_constraintTop_toTopOf="parent"
    app:layout_constraintBottom_toTopOf="@+id/bottomButtonId" <--Id of bottom button-->

For reference try this code:

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout 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">
    <androidx.core.widget.NestedScrollView
        android:layout_width="match_parent"
        android:layout_height="0dp"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        app:layout_constraintBottom_toTopOf="@+id/button6">
        <androidx.constraintlayout.widget.ConstraintLayout
            android:layout_width="match_parent"
            android:layout_height="wrap_content">
            <androidx.recyclerview.widget.RecyclerView
                android:id="@+id/rvMain"
                android:layout_width="match_parent"
                android:layout_height="wrap_content"
                android:overScrollMode="never"
                tools:listitem="@layout/imagepost_buttons"
                app:layout_constraintStart_toStartOf="parent"
                app:layout_constraintEnd_toEndOf="parent"
                app:layout_constraintTop_toTopOf="parent"
                app:layout_constraintBottom_toBottomOf="parent"/>
        </androidx.constraintlayout.widget.ConstraintLayout>
    </androidx.core.widget.NestedScrollView>

    <Button
        android:id="@+id/button6"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Bottom Button"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintBottom_toBottomOf="parent" />
</androidx.constraintlayout.widget.ConstraintLayout>