c# - Cast exception starting action mode in Xamarin Droid -

i'm having problem in xamarin droid app:

i have appcompatactivity fragment. fragment has recyclerview , item template linearlayout textview.

i handle long tap on recyclerview (inside fragment) , handler (minus not related code) is

private void onlistitemselect(int position) {     if (_actionmode == null)     {         try         {             _actionmode = (activity appcompatactivity).startsupportactionmode(this);         }         catch (exception ex)         {             toast.maketext(activity, ex.message, toastlength.long).show();         }     } } 

the problem when try start action mode (same issue startactionmode() instead of startsupportactionmode()) exception:

java.lang.classcastexception: android.support.v7.widget.fitwindowsframelayout cannot cast android.support.v7.widget.viewstubcompat

i can't seem find error , don't understand cause. ideas?

i attach other code snippets.

activity:

<?xml version="1.0" encoding="utf-8"?> <linearlayout xmlns:android="http://schemas.android.com/apk/res/android"     android:orientation="vertical"     android:layout_width="match_parent"     android:layout_height="match_parent">      <include         android:id="@+id/toolbar"         layout="@layout/app_bar" />      <framelayout         android:id="@+id/frame"         android:layout_width="match_parent"         android:layout_height="match_parent" />  </linearlayout> 

fragment:

<?xml version="1.0" encoding="utf-8"?> <framelayout xmlns:android="http://schemas.android.com/apk/res/android"     android:orientation="vertical"     android:layout_width="match_parent"     android:layout_height="match_parent">      <android.support.v7.widget.recyclerview         android:id="@+id/monthlist"         android:scrollbars="vertical"         android:layout_width="match_parent"         android:layout_height="match_parent"         android:background="@color/button_material_light" />  </framelayout>