Tutorial from google android "HelloTabWidget" has a null pointer error

When I view the following xml file in the layout view (eclispse), I got NullPointerException:null message, but when I run the code, it works, can anyone explain this to me why?

<TabHost xmlns:android="http://schemas.android.com/apk/res/android"
        android:id="@android:id/tabhost"
        android:layout_width="fill_parent"
        android:layout_height="fill_parent">
        <LinearLayout 
                    android:orientation="vertical"
                    android:layout_width="fill_parent"
                    android:layout_height="fill_parent"
                    android:padding="5dp">
        <TabWidget
            android:id="@android:id/tabs"
            android:layout_width="fill_parent"
            android:layout_height="wrap_content"/>
        <FrameLayout
            android:id="@android:id/tabcontent"
            android:layout_width="fill_parent"
            android:layout_height="fill_parent"
            android:padding="5dp"/>
        </LinearLayout>     
</TabHost开发者_如何学运维>

The problem is just that the Eclipse Layout view does not support TabHost controls yet.