Adapter for SearchView

SearchFilterAdapterBase.cs

public abstract class SearchFilterAdapterBase : MvxAdapter, IFilterable
{
    protected SearchFilterAdapterBase(Context context)
        : base(context) {}

    protected SearchFilterAdapterBase(Context context, IMvxAndroidBindingContext bindingContext)
        : base(context, bindingContext) {}

    protected abstract Filter CreateFilter();

    private Filter _filter;

    public Filter Filter
    {
        get { return this._filter ?? (this._filter = this.CreateFilter()); }
    }

    private readonly object _lock = new object();

    public object Lock
    {
        get { return this._lock; }
    }

    [MvxSetToNullAfterBinding]
    public IEnumerable FilteredSubset { get; set; }

    protected override void SetItemsSource(IEnumerable value)
    {
        lock (this.Lock)
        {
            this.FilteredSubset = null;
            base.SetItemsSource(value);
        }
    }

    public override int GetPosition(object item)
    {
        lock (this.Lock)
        {
            IEnumerable source = this.FilteredSubset ?? ItemsSource;
            return MvxEnumerableExtensions.GetPosition(source, item);
        }
    }

    public override object GetRawItem(int position)
    {
        lock (this.Lock)
        {
            IEnumerable source = this.FilteredSubset ?? ItemsSource;
            return MvxEnumerableExtensions.ElementAt(source, position);
        }
    }

    public override View GetView(int position, View convertView, ViewGroup parent)
    {
        lock (this.Lock)
        {
            return base.GetView(position, convertView, parent);
        }
    }

    public override int Count
    {
        get
        {
            lock (this.Lock)
            {
                return MvxEnumerableExtensions.Count(this.FilteredSubset ?? ItemsSource);
            }
        }
    }
}

public class SearchFilter<T> : Filter
{
    private readonly SearchFilterAdapterBase _adapter;

    public SearchFilter(SearchFilterAdapterBase adapter)
    {
        this._adapter = adapter;
    }

    public Func<T, string, bool> SearchFunc { get; set; }

    protected override FilterResults PerformFiltering(ICharSequence constraint)
    {
        // If there is no constraint return the original data set
        var returnObject = new FilterResults();
        if (constraint == null || constraint.Length() == 0)
            return returnObject;

        var results = new List<T>();

        try
        {
            lock (this._adapter.Lock)
            {
                if (this._adapter.ItemsSource.Count() > 0)
                {
                    IEnumerable<T> source = this._adapter.ItemsSource as IEnumerable<T>;
                    if (source == null)
                        return returnObject;

                    string c = constraint.ToString();

                    results.AddRange(source.Where(o => this.SearchFunc(o, c)));

                    returnObject.Values = FromArray(results.Select(r => r.ToJavaObject()).ToArray());
                    returnObject.Count = results.Count;
                }
            }
        }
        catch (System.Exception ex)
        {
            throw;
            var table = new Dictionary<string, string>();
            try
            {
                table.Add("constraint handle", constraint.Handle.ToString());
                if (constraint.Handle != IntPtr.Zero)
                    table.Add("constraint", constraint.ToString());
            }
            catch (System.Exception)
            {
                // Swallow
            }
            finally
            {
                Mvx.Resolve<IAppInsights>().Report(ex, table, ReportSeverity.Error);
            }

            throw;
        }
        finally
        {
            // Without the dispose GREFs go up, but maybe it contributes to the
            // Java GC destroying constraint before we're done using it.
            //constraint.Dispose();
        }

        return returnObject;
    }

    protected override void PublishResults(ICharSequence constraint, FilterResults results)
    {
        lock (this._adapter.Lock)
        {
            // Use the original data set if there is no constraint
            if (this._adapter.ItemsSource.Count() == 0 || constraint == null || constraint.Length() == 0)
            {
                // When there is nothing in the items source make sure
                // the filter is null.
                this._adapter.FilteredSubset = null;
                this._adapter.NotifyDataSetInvalidated();
            }
            else
            {
                using (var values = results.Values)
                {
                    this._adapter.FilteredSubset = values.ToArray<Java.Lang.Object>()
                        .Select(r => r.ToNetObject<T>()).ToList();
                }
            }

            this._adapter.NotifyDataSetChanged();
        }

        //constraint.Dispose();
        //results.Dispose();
    }
}

YourView.cs

public override void OnCreateOptionsMenu(IMenu menu, MenuInflater inflater)
{
    // The view pager sets this hint (through our parent fragment) so we need
    // to figure out if the menu items are visible or not.
    if (!UserVisibleHint)
        return;

    base.OnCreateOptionsMenu(menu, inflater);

    inflater.Inflate(Resource.Menu.ListMenu, menu);

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

    this._searchView = MenuItemCompat.GetActionView(searchMenu).JavaCast<SearchView>();
    this._searchView.QueryHint = "Search for assets.";
    this._searchView.LayoutParameters = new ActionBar.LayoutParams(GravityFlags.Right);

    this._searchView.QueryTextChange += (s, e) => { ViewModel.Constraint = e.NewText; };

    this._searchView.QueryTextSubmit += (s, e) => { e.Handled = true; };

    MenuItemCompat.SetOnActionExpandListener(searchMenu, new SearchViewExpandListener(this._adapter));
}

public string SearchTerm
{
    get { return ViewModel.Constraint; /* just to make the compiler happy */ }
    set
    {
        // Do not use string variant.
        // See: https://bugzilla.xamarin.com/show_bug.cgi?id=25995
        this._adapter.Filter.InvokeFilter(new Java.Lang.String(ViewModel.Constraint));
    }
}