An hien actionbar khi vuot ListView

<android.support.v7.widget.Toolbar        

  android:id="@+id/toolbar"        

  android:layout_width="match_parent"        

  android:layout_height="?attr/actionBarSize"        

  android:background="?attr/colorPrimary"       

  app:layout_scrollFlags="scroll|enterAlways" 

/>

app:layout_scrollFlags="scroll|enterAlways"