open-keychain/OpenKeychain/src/main/res/layout/qr_code_activity.xml

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:card_view="http://schemas.android.com/apk/res-auto"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <include
        android:id="@+id/toolbar_include"
        layout="@layout/toolbar_standalone" />

    <LinearLayout
        android:layout_below="@id/toolbar_include"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:orientation="vertical">

        <android.support.v7.widget.CardView
            android:id="@+id/qr_code_image_layout"
            android:transitionName="qr_code"
            android:layout_margin="32dp"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            card_view:cardBackgroundColor="@android:color/white"
            card_view:cardUseCompatPadding="true"
            card_view:cardCornerRadius="4dp">

            <org.sufficientlysecure.keychain.ui.widget.AspectRatioImageView
                android:id="@+id/qr_code_image"
                app:aspectRatioEnabled="true"
                android:layout_width="match_parent"
                android:layout_height="wrap_content"
                style="?android:attr/borderlessButtonStyle" />
        </android.support.v7.widget.CardView>

    </LinearLayout>
</RelativeLayout>