title: How can I resolve "No resource identifier found" for attributes in my Android project?
body: <p>I'm trying to implement a simple GridLayout in Xamarin Studio, as outlined in this example:</p>
  
  <p><a href="http://mobile.tutsplus.com/tutorials/android/android-user-interface-design-creating-a-numeric-keypad-with-gridlayout/" rel="nofollow">http://mobile.tutsplus.com/tutorials/android/android-user-interface-design-creating-a-numeric-keypad-with-gridlayout/</a></p>
  
  <pre><code>&lt;GridLayout xmlns:android="http://schemas.android.com/apk/res/android"
      android:layout_width="wrap_content"
      android:layout_height="wrap_content"
      android:layout_gravity="center"
      android:columnCount="4"
      android:orientation="horizontal" &gt;
      &lt;Button
          android:layout_column="3"
          android:text="/" /&gt;
      &lt;Button android:text="1" /&gt;
      &lt;Button android:text="2" /&gt;
      &lt;Button android:text="3" /&gt;
      &lt;Button android:text="*" /&gt;
      &lt;Button android:text="4" /&gt;
      &lt;Button android:text="5" /&gt;
      &lt;Button android:text="6" /&gt;
      &lt;Button android:text="-" /&gt;
      &lt;Button android:text="7" /&gt;
      &lt;Button android:text="8" /&gt;
      &lt;Button android:text="9" /&gt;
      &lt;Button
          android:layout_gravity="fill"
          android:layout_rowSpan="3"
          android:text="+" /&gt;
      &lt;Button
          android:layout_columnSpan="2"
          android:layout_gravity="fill"
          android:text="0" /&gt;
      &lt;Button android:text="00" /&gt;
      &lt;Button
          android:layout_columnSpan="3"
          android:layout_gravity="fill"
          android:text="=" /&gt;
  &lt;/GridLayout&gt;
  </code></pre>
  
  <p>but it won't build. I'm getting the following errors:</p>
  
  <blockquote>
  <pre><code> Error: No resource identifier found for attribute 'columnCount' in package 'android' (AndroidApplication1)
   Error: No resource identifier found for attribute 'layout_rowSpan' in package 'android' (AndroidApplication1)
   Error: No resource identifier found for attribute 'layout_columnSpan' in package 'android' (AndroidApplication1)
   Error: No resource identifier found for attribute 'layout_columnSpan' in package 'android' (AndroidApplication1)
  </code></pre>
  </blockquote>
  
  <p>What do I need to change to make this work?</p>