請參考紅色部份
<android.support.constraint.ConstraintLayout
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
...>
<textview ...> app:layout_constraintTop_toTopOf="parent" app:layout_constraintBottom_toBottomOf="parent" </textview> </ConstraintLayout>