app/src/main/res/layout/activity_image_preview.xml

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

    <uk.co.senab.photoview.PhotoView
        android:id="@+id/photo_view"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:paddingTop="@dimen/app_bar_size"
        android:scaleType="center"
        android:adjustViewBounds="true"
        android:background="@android:color/black" />

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:orientation="vertical">

        <android.support.v7.widget.Toolbar
            android:id="@+id/toolbar"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:background="#cc303030"
            android:elevation="@dimen/app_bar_elevation"
            android:theme="@style/ThemeOverlay.AppCompat.Dark.ActionBar"
            app:navigationIcon="@drawable/ic_arrow_back_white_24dp"
            app:title="@string/image_preview"
            app:popupTheme="@style/ThemeOverlay.AppCompat.Light" />

        <FrameLayout
            android:layout_width="match_parent"
            android:layout_height="match_parent">

            <com.pnikosis.materialishprogress.ProgressWheel
                android:id="@+id/progress_wheel"
                android:layout_width="64dp"
                android:layout_height="64dp"
                android:layout_gravity="center"
                app:matProg_barColor="@color/color_accent"
                app:matProg_progressIndeterminate="true"
                app:matProg_barWidth="4dp"
                app:matProg_fillRadius="true" />

        </FrameLayout>

    </LinearLayout>

</FrameLayout>