Create a layout for RegistrationActivity.kt named activity_registration.xml. Here I have added a UI, so please look at the full version of this file on GitHub. Here is a piece of code from this file:
<Button android:layout_width="match_parent" android:layout_height="wrap_content"
android:text="@string/title_reg"
android:id="@+id/reg_submit" android:layout_marginTop="32dp"
app:layout_constraintTop_toBottomOf="@+id/country_title_reg"
app:layout_constraintStart_toStartOf="parent" android:layout_marginStart="32dp"
app:layout_constraintEnd_toEndOf="parent" android:layout_marginEnd="32dp"/>
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</android.support.constraint.ConstraintLayout>
</ScrollView>
</android.support.v7.widget.CardView>
</android.support.constraint.ConstraintLayout>
Here is the image preview of this layout: