Center components in ConstraintLayout
<p>I am pretty sure that <code>ConstraintLayout</code> should not be used for use case described below, but, for sake of discussion, what would be the best way to center vertically aligned components in <code>ConstraintLayout</code> (as it is possible in <code>LinearLayout</code> with gravity set to "center" and vertical orientation) ?</p>

<p>It is possible to center single component by adding constraints to all four sides. It will position it perfectly in center of the screen. But if we have multiple components mutually constrained, then it starts to be tricky since all components will tend to overlap (if constrained to top and bottom, which is expected behavior) or newly added component will be below centered component (or above). </p>

<p>I have end-up with solution that does not feel to be perfect, by adding one component above, and one below to the centered component. That way components will be aligned vertically and almost centered :).</p>

<p>Here is an example: </p>

<ol>
<li>Centered component:</li>
</ol>

<p><a href="https://i.stack.imgur.com/fgaKZ.jpg" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/fgaKZ.jpg" alt="Centered component"></a></p>

<ol start="2">
<li>Component above, constrained to center</li>
</ol>

<p><a href="https://i.stack.imgur.com/8VK3H.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/8VK3H.png" alt="enter image description here"></a></p>

<ol start="3">
<li>Component below, constrained to center</li>
</ol>

<p><a href="https://i.stack.imgur.com/bIYbI.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/bIYbI.png" alt="enter image description here"></a></p>

<p>Other components placed above and below are constrained respectively to the nearest component (above or below).
As you can see on first image, components are not perfectly centered, because there are three components below and two components above "Country" field. 
Any designer will notice this :), so is it possible to use <code>ConstraintLayout</code> and to center whole group of components (or it is not meant to work like this)</p>

<p>P.S.
<code>LinearLayout</code> with <code>gravity="center"</code> is probably the best solution for this case.</p>