Add a fixed view to appear at the top of the list. If addHeaderView is called more than once, the views will appear in the order they were added. Views added using this call can take focus if they want.

Note: When first introduced, this method could only be called before setting the adapter with ListView.Adapter. Starting with NoType:android/os/Build$VERSION_CODES;Href=../../../reference/android/os/Build.VERSION_CODES.html#KITKAT, this method may be called at any time. If the ListView's adapter does not extend Android.Widget.HeaderViewListAdapter, it will be wrapped with a supporting instance of Android.Widget.IWrapperListAdapter.

[Android Documentation]