Specified cast is invalid Xamarin Listview

I am using this link (https://canbilgin.wordpress.com/2018/03/17/re-order-listview-items-with-drag-drop-ii/) for drag and drop feature in Xamarin Forms Listview items. I'm getting the error "Specified cast is invalid" in this line _listAdapter = ((AWidget.IWrapperListAdapter)_listView.Adapter).WrappedAdapter;
The post author said

// NOTE: careful, the listAdapter might not always be an IWrapperListAdapter

What does it mean by "listAdapter ....not always be an IWrapperListAdapter"? How do I get rid of this?

Please provide me with any solution, thanks in advance