activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.ConstraintLayout 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"
    tools:context="com.codingtrickshub.checkboxlistview.MainActivity">

    <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:orientation="vertical"
        android:weightSum="100">

        <ListView
            android:id="@+id/category_listView"
            android:layout_width="fill_parent"
            android:layout_height="fill_parent"
            android:layout_weight="80"/>

        <Button
            android:id="@+id/selectCategoryButton"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:layout_gravity="center"
            android:text="Submit"
            android:layout_weight="20"/>

    </LinearLayout>

</android.support.constraint.ConstraintLayout>