Quelle  activity_media_viewer.xml

<?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"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:background="@color/gallery_background">

    <ch.threema.app.ui.LockableViewPager
        android:id="@+id/pager"
        android:layout_width="match_parent"
        android:layout_height="match_parent" />

    <LinearLayout
        android:id="@+id/session_loading"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_gravity="top|center_horizontal"
        android:layout_marginTop="10dp"
        android:orientation="horizontal"
        android:visibility="gone">

        <com.google.android.material.progressindicator.CircularProgressIndicator
            android:id="@+id/progress_bar"
            style="@style/Widget.Material3.CircularProgressIndicator.Small"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_marginTop="2dp"
            android:indeterminate="true" />

        <TextView
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_marginLeft="10sp"
            android:text="@string/decoding_message"
            android:textColor="@android:color/white" />
    </LinearLayout>

    <FrameLayout
        android:id="@+id/caption_container"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_gravity="bottom"
        android:paddingHorizontal="@dimen/grid_unit_x2"
        android:paddingBottom="@dimen/mediaviewer_caption_border_bottom"
        android:visibility="gone"
        tools:visibility="visible">

        <com.google.android.material.card.MaterialCardView
            style="@style/Threema.CardView.MediaViewerCaption"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_gravity="center_horizontal">

            <ch.threema.app.emojis.EmojiTextView
                android:id="@+id/caption"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:ellipsize="end"
                android:maxLines="1"
                android:paddingHorizontal="@dimen/grid_unit_x2"
                android:paddingVertical="@dimen/mediaviewer_caption_container_padding_vertical"
                android:textAppearance="@style/TextAppearance.Material3.BodyLarge"
                android:textColor="?attr/colorOnBackground"
                tools:text="This is the caption"
                tools:textColor="@android:color/white" />

        </com.google.android.material.card.MaterialCardView>


    </FrameLayout>

    <com.google.android.material.appbar.AppBarLayout
        android:id="@+id/appbar"
        android:layout_width="match_parent"
        android:layout_height="wrap_content">

        <com.google.android.material.appbar.MaterialToolbar
            android:id="@+id/toolbar"
            android:layout_width="match_parent"
            android:layout_height="?attr/actionBarSize"
            android:theme="@style/ThemeOverlay.AppCompat.ActionBar"
            app:popupTheme="@style/Threema.PopupMenuStyle.Overflow" />

    </com.google.android.material.appbar.AppBarLayout>

</FrameLayout>