Quelle  activity_qrscanner.xml

<?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:id="@+id/root_view"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".camera.QRScannerActivity">

    <androidx.camera.view.PreviewView
        android:id="@+id/camera_preview"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintTop_toTopOf="parent" />

    <View
        android:id="@+id/border_frame_top"
        android:layout_width="match_parent"
        android:layout_height="0dp"
        android:background="@color/qrscanner_masking_color"
        app:layout_constraintBottom_toTopOf="@+id/camera_preview_container"
        app:layout_constraintTop_toTopOf="parent" />

    <View
        android:id="@+id/border_frame_bottom"
        android:layout_width="match_parent"
        android:layout_height="0dp"
        android:background="@color/qrscanner_masking_color"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/camera_preview_container" />

    <View
        android:id="@+id/border_frame_left"
        android:layout_width="0dp"
        android:layout_height="0dp"
        android:background="@color/qrscanner_masking_color"
        app:layout_constraintBottom_toTopOf="@id/border_frame_bottom"
        app:layout_constraintEnd_toStartOf="@+id/camera_preview_container"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@id/border_frame_top" />

    <View
        android:id="@+id/border_frame_right"
        android:layout_width="0dp"
        android:layout_height="0dp"
        android:background="@color/qrscanner_masking_color"
        app:layout_constraintBottom_toTopOf="@id/border_frame_bottom"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toEndOf="@+id/camera_preview_container"
        app:layout_constraintTop_toBottomOf="@id/border_frame_top" />

    <ImageView
        android:id="@+id/camera_viewfinder"
        android:layout_width="0dp"
        android:layout_height="0dp"
        android:layout_marginLeft="-8dp"
        android:layout_marginTop="-8dp"
        android:layout_marginRight="-8dp"
        android:layout_marginBottom="-8dp"
        android:importantForAccessibility="no"
        android:src="@drawable/qr_viewfinder"
        app:layout_constraintBottom_toBottomOf="@+id/camera_preview_container"
        app:layout_constraintLeft_toLeftOf="@+id/camera_preview_container"
        app:layout_constraintRight_toRightOf="@+id/camera_preview_container"
        app:layout_constraintTop_toTopOf="@+id/camera_preview_container" />

    <androidx.constraintlayout.widget.ConstraintLayout
        android:id="@+id/camera_preview_container"
        android:layout_width="0dp"
        android:layout_height="match_parent"
        android:layout_marginTop="@dimen/qrscanner_masking_margin_top"
        android:layout_marginBottom="@dimen/qrscanner_masking_margin_bottom"
        app:layout_constraintDimensionRatio="1:1"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toRightOf="parent">

    </androidx.constraintlayout.widget.ConstraintLayout>

    <TextView
        android:id="@+id/hint_view"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:layout_marginHorizontal="@dimen/grid_unit_x8"
        android:gravity="center_horizontal"
        android:paddingHorizontal="@dimen/grid_unit_x2"
        android:paddingVertical="@dimen/grid_unit_x1"
        android:textAlignment="center"
        android:textAppearance="@style/Threema.TextAppearance.BodyMedium"
        android:textColor="@android:color/white"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toRightOf="parent"
        app:layout_constraintTop_toBottomOf="@id/camera_preview_container"
        tools:text="@string/msg_default_status" />

</androidx.constraintlayout.widget.ConstraintLayout>