SearchViewModel with ReactiveUI

SearchViewModel.cs

using ReactiveUI;
using System.Threading.Tasks;
using System.Windows.Input;
using TwitterFeedAPI;

namespace FeedManagement.WPF.Search
{
    public class SearchViewModel : ReactiveObject, ISearchViewModel
    {
        public IScreen HostScreen { get; protected set; }
        public ICommand SearchCommand { get; private set; }
        public Twitter _twitterAPI = new Twitter();

        public SearchViewModel(IScreen screen)
        {
            HostScreen = screen;
            SearchCommand = new ReactiveCommand();
            
            (SearchCommand as ReactiveCommand).RegisterAsyncTask(t =>
                {
                    return Task.Factory.StartNew(() =>
                        {
                            SearchResult = _twitterAPI.SearchFor(SearchText);
                        });
                });


        }

        private string _SearchResult;
        public string SearchResult
        {
            get { return _SearchResult; }
            set { this.RaiseAndSetIfChanged(ref _SearchResult, value); }
        }

        public string SearchText { get; set; }
    }
}