ConstraintLayout - how to align centers of two views vertically

Android Studio 3.5

If it's TL;TR...

Select your desired views, right button :

And you'll get:

1. Without Guideline, put attributes on every views that you need to align vertically.

   app:layout_constraintTop_toTopOf="parent"
   app:layout_constraintBottom_toBottomOf="parent"
   

2. With Guideline

Add horizontal Guideline and make it vertically center with layout_constraintGuide_percent.

<androidx.constraintlayout.widget.Guideline
     android:id="@+id/guideline"
     android:layout_width="1dp"
     android:layout_height="wrap_content"
     android:orientation="horizontal"
     app:layout_constraintGuide_percent="0.5"/>

For every views, anchor them to guideline with attributes

app:layout_constraintTop_toTopOf="@id/guideline"
app:layout_constraintBottom_toBottomOf="@id/guideline"

With guideline, you have more flexibility, as you can change all views position easily by moving the guideline.

Update:

To align a view vertically center against another view then you just need to refer the view id in attribute. To align txt_change_picture vertically center against img_change_picture, you can change layout like this:

<TextView
    android:id="@+id/txt_change_picture"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    app:layout_constraintStart_toEndOf="@id/guideline_text"
    android:text="@string/settings_main_change_picture"

    app:layout_constraintTop_toTopOf="@id/img_change_picture"
    app:layout_constraintBottom_toBottomOf="@id/img_change_picture"

/>