How to get a String from searchView on ToolBar?

I need to get a String from searchView on ToolBar for filtering, I complete the filtering but ı can’t get the String from ToolBar.

Here is my searchView

<item
        android:title="Search"
        android:id="@+id/menu_search"
        android:icon="@android:drawable/ic_menu_search"
        app:showAsAction="always|collapseActionView"
        app:actionViewClass="androidx.appcompat.widget.SearchView"
        />

Here is my RecylerAdapter

 val userInput: String = ""
        val filteredList: List<Book> = bookList.filter {
            it.bookName.contains(userInput)
        }

So I need userInput.