title: monodroid/xamarin custom attributes are empty using ObtainStyledAttributes
body: <p>Trying to pass a custom attribute from a parent layout to a child layout.</p>
  
  <p>The TypedArray returned from ObtainStyledAttributes() doesn't seem to have the corresponding custom values for the custom properties I've created, although I can map their IDs to the values in Resource.designer.</p>
  
  <hr>
  
  <p>Attr.xml:</p>
  
  <pre><code>&lt;resources&gt;
  &lt;declare-styleable name="HeaderView"&gt;
      &lt;attr name="bgcolor" format="color" /&gt;
      &lt;attr name="testing" format="string" /&gt;
  &lt;/declare-styleable&gt;
  </code></pre>
  
  <p>Main.xaml:</p>
  
  <pre><code>&lt;RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
  xmlns:custom="http://schemas.android.com/apk/res"&gt;
      &lt;LinearLayout
          android:orientation="vertical"
          android:layout_width="fill_parent"
          android:layout_height="fill_parent"&gt;
          &lt;views.HeaderView
              android:id="@+id/hdrWatchList"
              android:layout_width="fill_parent"
              android:layout_height="20.0dp"
              custom:bgcolor="@color/blue"
              custom:testing="testing text buddy" /&gt;
  </code></pre>
  
  <p>View Class:</p>
  
  <pre><code>    public HeaderView (Context context, IAttributeSet attrs) :
          base (context, attrs)
      {
          int[] styleAttrs = Resource.Styleable.HeaderView;
          TypedArray a = context.ObtainStyledAttributes(attrs, styleAttrs);
  
          string  sid = a.GetString(Resource.Styleable.HeaderView_testing);
          int  id = a.GetColor(Resource.Styleable.HeaderView_bgcolor, 555);
  
          Log.Info( "testing", "resource sid : " + sid); // RETURNS ''
          Log.Info( "testing", "resource id : " + id); // RETURNS DEF 555
  </code></pre>