FossifyGallery/app/src/main/res/layout/activity_photos.xml

<?xml version="1.0" encoding="utf-8"?>
<android.support.design.widget.CoordinatorLayout
    android:id="@+id/coordinator_layout"
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <GridView
        android:id="@+id/photos_grid"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:background="@android:color/black"
        android:choiceMode="multipleChoiceModal"
        android:columnWidth="@dimen/photo_tmb_size"
        android:horizontalSpacing="1dp"
        android:numColumns="auto_fit"
        android:stretchMode="columnWidth"
        android:verticalSpacing="1dp"/>

</android.support.design.widget.CoordinatorLayout>