See below menu xml file,
<?xml version="1.0" encoding="utf-8"?>
<menu xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto">
<item android:title="Search"
android:id="@+id/search_menu"
android:icon="@android:drawable/ic_menu_search"
app:actionViewClass="android.widget.SearchView"
app:showAsAction="always"/>
That let me confused, if using android:actionViewClass, I will get error like searchview is null, but using app:actionViewClass, everything seems fine. So I am wondering why and differences between android:actionViewClass and app:actionViewClass.