res/layout/app_grid_item.xml

<?xml version="1.0" encoding="utf-8"?>
<!--  Copyright (C) 2016 The OmniROM Project

  This program is free software: you can redistribute it and/or modify
  it under the terms of the GNU General Public License as published by
  the Free Software Foundation, either version 2 of the License, or
  (at your option) any later version.

  This program is distributed in the hope that it will be useful,
  but WITHOUT ANY WARRANTY; without even the implied warranty of
  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  GNU General Public License for more details.

  You should have received a copy of the GNU General Public License
  along with this program.  If not, see <http://www.gnu.org/licenses/>.
 -->
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <ImageView
        android:id="@+id/appIcon"
        android:layout_width="@android:dimen/app_icon_size"
        android:layout_height="@android:dimen/app_icon_size"
        android:layout_alignParentLeft="true"
        android:layout_alignParentStart="true"
        android:layout_alignParentTop="true"
        android:background="?android:attr/selectableItemBackground"
        android:scaleType="centerInside" />
</RelativeLayout>