title: GridLayout in Android
body: <p>I just created a new android application, so I only have the MainActivity.java file and its corresponding xml layout file (activity_main.xml). The contents of the activity_main.xml file is:</p>
  
  <pre><code>&lt;GridLayout xmlns:android="http://schemas.android.com/apk/res/android"
  android:layout_width="match_parent"
  android:layout_height="match_parent"
  android:columnCount="2"
  android:orientation="vertical"
  android:rowCount="2" &gt;
  
  &lt;Button
      android:id="@+id/blueButton"
      android:background="#236B8E" /&gt;
  
  &lt;Button
      android:id="@+id/redButton"
      android:background="#FF0000" /&gt;
  
  &lt;Button
      android:id="@+id/yellowButton"
      android:background="#FFFF00" /&gt;
  
  &lt;Button
      android:id="@+id/greenButton"
      android:background="#00FF00" /&gt;
  
  &lt;/GridLayout&gt;
  </code></pre>
  
  <p>When I run the application, all I see is a white screen with the "Main Activity" bar at the top. Is there anything wrong with my xml file?</p>