title: Constraint layout chain packed usage
body: <p>I'm trying to centre two textviews vertically using constraint layout chains. I know I can wrap the text layouts in a linear layout but I wanted to try out the new chain feature. When I build my project though I get an error, <code>Error:(28, 50) No resource found that matches the given name (at 'layout_constraintBottom_toTopOf' with value '@id/item_school_location').</code></p>
  
  <pre><code>&lt;?xml version="1.0" encoding="utf-8"?&gt;
  &lt;layout xmlns:android="http://schemas.android.com/apk/res/android"
      xmlns:app="http://schemas.android.com/apk/res-auto"&gt;
  
      &lt;android.support.constraint.ConstraintLayout
          android:layout_width="match_parent"
          android:layout_height="72dp"&gt;
  
          &lt;ImageView
              android:id="@+id/item_school_logo"
              android:layout_width="48dp"
              android:layout_height="48dp"
              android:layout_marginStart="16dp"
              android:contentDescription="@string/item_school_logo_description"
              app:layout_constraintBottom_toBottomOf="parent"
              app:layout_constraintLeft_toLeftOf="parent"
              app:layout_constraintTop_toTopOf="parent"
              app:layout_constraintVertical_bias="0.5" /&gt;
  
          &lt;TextView
              android:id="@+id/item_school_name"
              android:layout_width="wrap_content"
              android:layout_height="wrap_content"
              android:layout_marginEnd="16dp"
              android:layout_marginStart="72dp"
              android:maxLines="1"
              android:textAppearance="@style/TextAppearance.AppCompat.Light.SearchResult.Subtitle"
              app:layout_constraintBottom_toTopOf="@id/item_school_location"
              app:layout_constraintLeft_toLeftOf="parent"
              app:layout_constraintTop_toTopOf="parent"
              app:layout_constraintVertical_bias="0.5"
              app:layout_constraintVertical_chainPacked="true" /&gt;
  
          &lt;TextView
              android:id="@+id/item_school_location"
              android:layout_width="wrap_content"
              android:layout_height="wrap_content"
              android:layout_marginEnd="16dp"
              android:layout_marginStart="72dp"
              android:maxLines="1"
              android:textAppearance="@style/TextAppearance.AppCompat.Small"
              android:textSize="16sp"
              app:layout_constraintBottom_toBottomOf="parent"
              app:layout_constraintLeft_toLeftOf="parent"
              app:layout_constraintTop_toBottomOf="@id/item_school_name" /&gt;
      &lt;/android.support.constraint.ConstraintLayout&gt;
  &lt;/layout&gt;
  </code></pre>
  
  <p>Anyone know what's causing this error?</p>