XML命名空间+无法解析

Question

我试图创建一个新的drawable'round_button.xml'

<?xml version="1.0" encoding="utf-8"?>
<!-- Created by Stephen Murby   [06.07.2013] -->
<!-- Documentation:     http://developer.android.com/guide/topics/resources/drawable-resource.html -->
<shape xmlns:android="http://schemas.android.com/apk/res/android" 
    android:shape="ring"
    android:innerRadius="0px">  <!-- Dimension Value only NOT an Integer -->

    <!-- Use android:startColor for centre value, moving to android:endColor as the outer. -->
    <gradient 
        android:type="radial"/>

</shape>

这位于'res / drawable / circle_button.xml'。然后我尝试在我的'activity_main.xml'中创建一个实例。

我怎么会收到这些错误：

Error
Sat Jul 06 15:22:16 BST 2013
activity_fullscreen.xml: Failed to parse file .../res/drawable/circle_button.xml
Error
Sat Jul 06 15:22:16 BST 2013
activity_fullscreen.xml: Failed to convert @drawable/circle_button into a drawable