activity_custom_scanner.xml

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout 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">

    <com.journeyapps.barcodescanner.DecoratedBarcodeView
        android:id="@+id/zxing_barcode_scanner"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        app:zxing_scanner_layout="@layout/custom_barcode_scanner">
    </com.journeyapps.barcodescanner.DecoratedBarcodeView>

    <Button
        android:id="@+id/switch_flashlight"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="@string/turn_on_flashlight"
        android:layout_alignParentTop="true"
        android:layout_centerHorizontal="true"
        android:onClick="switchFlashlight"/>

</RelativeLayout>