title: Android Constraint Layout - Alignment of childrens
body: <p>So I have a constraint layout with height <code>wrap_content</code> and width <code>match_parent</code>. I would like to know </p>
  
  <ol>
  <li><p>How to align a <code>button</code> to the <strong>centre</strong> of a <code>recycler view</code> if they are rendered horizontally.</p></li>
  <li><p>How to align a <code>button</code> to the <strong>centre</strong> of a <code>LinearLayout</code>(which will be populated later).. if they are rendered horizontally.</p></li>
  </ol>
  
  <p>I tried <code>constraint.Guideline</code> but it seems not working because of constraint layout  <code>wrap_content</code> height. any suggestions?</p>