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"
        xmlns:app="http://schemas.android.com/apk/res-auto"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        tools:context="org.nixan.sandboxapp.MainActivity">

    <EditText
            android:layout_width="300dp"
            android:layout_height="wrap_content"
            android:id="@+id/testEdit"
            app:layout_constraintBottom_toBottomOf="parent"
            app:layout_constraintLeft_toLeftOf="parent"
            app:layout_constraintRight_toRightOf="parent"
            app:layout_constraintTop_toTopOf="parent"/>

    <Button android:layout_width="wrap_content" android:layout_height="wrap_content"
            android:id="@+id/triggerButton" android:text="@string/test"
            app:layout_constraintBottom_toBottomOf="parent"
            app:layout_constraintLeft_toLeftOf="parent"
            app:layout_constraintRight_toRightOf="parent"/>

</android.support.constraint.ConstraintLayout>