In an xml layout file, the xmlns is already defined, but I get this error at compile time: No resource identifier found for attribute. Why is that? thanks

I'm following a Facebook dev tutorial on facebook site <https://developers.facebook.com/docs/getting-started/facebook-sdk-for-android/3.0/> the layout file is as follows:

```
   <ScrollView xmlns:android="http://schemas.android.com/apk/res/android"
        xmlns:app="http://schemas.android.com/apk/res-auto"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    >

    <com.facebook.widget.ProfilePictureView
            android:id="@+id/profilepic"
            android:layout_height="wrap_content"
            android:layout_width="0dp"
            android:layout_weight="1"
            app:preset_size="large" app:is_cropped="true"
    />
   </ScrollView>

```