title: Constraint layout button text center alignment
body: <p>I'm using the new <code>Constraint</code> layout to build my layout. I need to have <code>Button</code> that occupies almost the entire screen width and that was easy using constraints.</p>
  
  <p><a href="https://i.stack.imgur.com/Wbdmd.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/Wbdmd.png" alt="enter image description here"></a></p>
  
  <p>As you can see in the image I am setting the width to <code>0dp</code> (Any size), but the text don't stick at the center what's usually the normal for a button text.</p>
  
  <p>I've tried:
   - set gravity to center
   - set textAlignment to center</p>
  
  <p>Looks like this properties can't work with <code>0dp</code> width (Any size).</p>
  
  <p>So I've tried to set the width to <code>match_parent</code> using gravity center.</p>
  
  <p><a href="https://i.stack.imgur.com/826Tx.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/826Tx.png" alt="enter image description here"></a></p>
  
  <p>It's a little bit to the right.</p>
  
  <p>Does any one know how to fix that behavior ? </p>
  
  <p>Note that i'm using alpha4</p>
  
  <p><code>compile 'com.android.support.constraint:constraint-layout:1.0.0-alpha4'</code></p>
  
  <p>XML code</p>
  
  <pre><code>&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/content_login"
      android:layout_width="match_parent"
      android:layout_height="wrap_content"
      tools:context="br.com.marmotex.ui.LoginActivityFragment"
      tools:showIn="@layout/activity_login"&gt;
  
      &lt;Button
          android:text="Log in"
          android:layout_width="0dp"
          android:layout_height="wrap_content"
          android:id="@+id/btLogin"
          android:layout_marginTop="48dp"
          app:layout_constraintTop_toBottomOf="@+id/textView6"
          android:layout_marginEnd="16dp"
          app:layout_constraintRight_toRightOf="@+id/content_login"
          android:layout_marginRight="16dp"
          android:layout_marginStart="16dp"
          app:layout_constraintLeft_toLeftOf="@+id/content_login"
          android:layout_marginLeft="16dp"
          android:textColor="@android:color/white"
          android:background="@color/BackgroundColor" /&gt;
  
  &lt;/android.support.constraint.ConstraintLayout&gt;
  </code></pre>
  
  <p><strong>EDIT</strong> It was a bug in <code>ConstraintLayout</code> alpha4.</p>
  
  <p><strong>UPDATE</strong> Google has released <strong>alpha5</strong>, the above code now Works.
  <a href="http://tools.android.com/recent/constraintlayout-alpha5available" rel="nofollow noreferrer">Release note</a></p>