activity_dialog_demo.xml

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools" android:layout_width="match_parent"
    android:layout_height="match_parent" android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    android:paddingBottom="@dimen/activity_vertical_margin"
    tools:context="com.dennism.DialogDemoActivity">

    <Button
        android:id="@+id/button1"
        android:text="show"
        android:layout_centerInParent="true"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content" />

</RelativeLayout>