Small sample showing how to use SearchView with the Support v7 ActionBar. See the tutorial here: http://youtu.be/4FvObC44bhM

gistfile1.cs

// Add this to the OnCreateOptionsMenu, where item is = menu.FindItem(Resource.Id.action_search);

MenuItemCompat.SetOnActionExpandListener(item, new SearchViewExpandListener(_adapter));

Main.axml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent">
    <ListView
        android:id="@+id/listView"
        android:layout_width="fill_parent"
        android:layout_height="fill_parent" />
</LinearLayout>

main.xml

<?xml version="1.0" encoding="utf-8"?>
<menu xmlns:android="http://schemas.android.com/apk/res/android"
      xmlns:app="http://schemas.android.com/apk/res-auto">
  <item android:id="@+id/action_search"
        android:title="Search"
        android:icon="@android:drawable/ic_menu_search"
        app:showAsAction="always|collapseActionView"
        app:actionViewClass="android.support.v7.widget.SearchView" />
</menu>

SearchViewActivity.cs

using Android.App;
using Android.Runtime;
using Android.Support.V4.View;
using Android.Support.V7.App;
using Android.Support.V7.Widget;
using Android.Views;
using Android.OS;
using Android.Widget;

namespace SearchViewSample
{
    [Activity(Label = "SearchView Sample", MainLauncher = true, Icon = "@drawable/icon",
        Theme = "@style/Theme.AppCompat.Light")]
    public class SearchViewActivity : ActionBarActivity
    {
        private SearchView _searchView;
        private ListView _listView;
        private ArrayAdapter _adapter;

        protected override void OnCreate(Bundle bundle)
        {
            base.OnCreate(bundle);

            // Set our view from the "main" layout resource
            SetContentView(Resource.Layout.Main);

            var products = new[]
            {
                "Dell Inspiron", "HTC One X", "HTC Wildfire S", "HTC Sense", "HTC Sensation XE",
                "iPhone 4S", "Samsung Galaxy Note 800",
                "Samsung Galaxy S3", "MacBook Air", "Mac Mini", "MacBook Pro"
            };

            _listView = FindViewById<ListView>(Resource.Id.listView);
            _adapter = new ArrayAdapter<string>(this, Android.Resource.Layout.SimpleListItem1, products);
            _listView.Adapter = _adapter;
        }

        public override bool OnCreateOptionsMenu(IMenu menu)
        {
            MenuInflater.Inflate(Resource.Menu.main, menu);

            var item = menu.FindItem(Resource.Id.action_search);

            var searchItem = MenuItemCompat.GetActionView(item);
            _searchView = searchItem.JavaCast<SearchView>();

            _searchView.QueryTextChange += (s, e) => _adapter.Filter.InvokeFilter(e.NewText);

            _searchView.QueryTextSubmit += (s, e) =>
            {
                //TODO: Do something fancy when search button on keyboard is pressed
                Toast.MakeText(this, "Searched for: " + e.Query, ToastLength.Short).Show();
                e.Handled = true;
            };

            return true;
        }
    }
}

SearchViewExpandListener.cs

public class SearchViewExpandListener 
    : Java.Lang.Object, MenuItemCompat.IOnActionExpandListener
{
    private readonly IFilterable _adapter;

    public SearchViewExpandListener(IFilterable adapter)
    {
        _adapter = adapter;
    }

    public bool OnMenuItemActionCollapse(IMenuItem item)
    {
        _adapter.Filter.InvokeFilter("");
        return true;
    }

    public bool OnMenuItemActionExpand(IMenuItem item)
    {
        return true;
    }
}

@wgrand - Exception still appear even though you change to Android.Support.V7.Widget.SearchView...

To Solve the problem, I used MenuItemCompat instead of JavaCast():

SearchView searchView = (SearchView)MenuItemCompat.GetActionView(searchItem);

Hi everyone,
var searchItem = MenuItemCompat.GetActionView(item);
alxays returns null for me, does any one have the same problem ?

how i can do it use _adapter = new FriendAdapter(this, Android.Resource.Layout.SimpleListItem1, products);