Android showAsAction: always doesn't work

If you use Android Support, it will no work as below.

<menu xmlns:android="http://schemas.android.com/apk/res/android" >
 <item android:id="@+id/action_1"
 android:icon="@drawable/ic_action_1"
 android:showAsAction="ifRoom"
 android:title="@string/menu_1"></item>
</menu>

Solution:

Add xmlns:app="http://schemas.android.com/apk/res-auto", and use app:showAsAction instead of android:showAsAction

<menu xmlns:android="http://schemas.android.com/apk/res/android" xmlns:app="http://schemas.android.com/apk/res-auto" >

 <item android:id="@+id/action_1"

  android:icon="@drawable/ic_action_1"

  app:showAsAction="ifRoom"

  android:title="@string/menu_undo"></item>

</menu>