title: cant position FrameLayout inside ConstraintLayout
body: <p>Building main app layout that should have:</p>
  
  <p>1) ConstraintLayout as root - because its new and trending changer of RelativeLayout</p>
  
  <p>2) AppBarLayout with toolbar inside</p>
  
  <p>3) BottomNavigationView at the bottom ofc</p>
  
  <p>4) FAB at bottom right above BNV</p>
  
  <p>5) And FrameLayout - container for my fragments that must be between AppBarLayout and BottomNavigationView.</p>
  
  <p>I cant position my FrameLayout. It appears only match_parent with full device size or 0dp.</p>
  
  <pre><code>&lt;?xml version="1.0" encoding="utf-8"?&gt;
  &lt;android.support.constraint.ConstraintLayout 
  xmlns:android="http://schemas.android.com/apk/res/android"
      xmlns:app="http://schemas.android.com/apk/res-auto"
      xmlns:tools="http://schemas.android.com/tools"
      android:id="@+id/main_layout"
      android:layout_width="match_parent"
      android:layout_height="match_parent"&gt;
  
      &lt;android.support.design.widget.AppBarLayout
          android:id="@+id/appbar"
          android:layout_width="match_parent"
          android:layout_height="wrap_content"
          android:paddingTop="@dimen/appbar_padding_top"
          android:theme="@style/AppTheme.AppBarOverlay"
          app:layout_constraintTop_toTopOf="@+id/frame_container"&gt;
  
          &lt;android.support.v7.widget.Toolbar
              android:id="@+id/toolbar"
              android:layout_width="match_parent"
              android:layout_height="?attr/actionBarSize"
              android:layout_weight="1"
              android:background="?attr/colorPrimary"
              app:layout_scrollFlags="scroll|enterAlways"
              app:popupTheme="@style/AppTheme.PopupOverlay"
              app:title="@string/app_name"&gt;
  
          &lt;/android.support.v7.widget.Toolbar&gt;
  
      &lt;/android.support.design.widget.AppBarLayout&gt;
  
      &lt;FrameLayout
          android:id="@+id/frame_container"
          android:layout_width="match_parent"
          android:layout_height="match_parent"
          app:layout_behavior="@string/appbar_scrolling_view_behavior"
          app:layout_constraintTop_toTopOf="parent"&gt;
  
      &lt;/FrameLayout&gt;
  
  
      &lt;android.support.design.widget.FloatingActionButton
          android:id="@+id/floatingActionButton"
          android:layout_width="wrap_content"
          android:layout_height="wrap_content"
          android:layout_gravity="bottom|end"
          android:layout_marginBottom="8dp"
          android:layout_marginEnd="8dp"
          android:clickable="true"
          android:focusable="true"
          app:layout_constraintBottom_toTopOf="@+id/navigation"
          app:layout_constraintEnd_toEndOf="parent"
          app:srcCompat="@drawable/ic_home_black_24dp" /&gt;
  
      &lt;android.support.design.widget.BottomNavigationView
          android:id="@+id/navigation"
          android:layout_width="match_parent"
          android:layout_height="wrap_content"
          android:layout_gravity="bottom"
          android:background="@color/primary"
          app:elevation="8dp"
          app:itemIconTint="@color/icons"
          app:itemTextColor="@color/icons"
          app:layout_constraintBottom_toBottomOf="@+id/frame_container"
          app:layout_insetEdge="bottom"
          app:menu="@menu/navigation" /&gt;
  
  &lt;/android.support.constraint.ConstraintLayout&gt;
  </code></pre>