title: Android: Custom font works for TextView, not for Button
body: <p>I cannot get a Button to use my custom font.
  It works fine with a TextView, not with a Button (which is a subclass of TextView).</p>
  
  <p>I am using Android Studio 3.1.2 with minSdkVersion 26 and Kotlin.</p>
  
  <p><em>res/font/font.xml</em></p>
  
  <pre><code>&lt;?xml version="1.0" encoding="utf-8"?&gt;
  &lt;font-family xmlns:android="http://schemas.android.com/apk/res/android"&gt;
      &lt;font
          android:fontStyle="normal"
          android:fontWeight="400"
          android:font="@font/my-custom-font" /&gt;
  &lt;/font-family&gt;
  </code></pre>
  
  <p><em>res/layout/fragment.xml</em></p>
  
  <pre><code>...
  &lt;TextView
      android:layout_width="wrap_content"
      android:layout_height="wrap_content"
      android:id="@+id/myButton"
      android:maxWidth="30dp"
      android:minWidth="30dp"
      android:maxHeight="40dp"
      android:minHeight="40dp"
      android:fontFamily="@font/my-custom-font"
      android:textSize="20dp"
      android:text="a" /&gt;
  ...
  </code></pre>
  
  <p>The above works. Replace TextView with Button and it stops working.</p>
  
  <p>Edit: I want to use a custom font to hold the icons for our Buttons, instead of using images and ImageButtons.  We find a custom font is easier to manage than images.</p>