public MainPageFragmentViewModel (INavigationService navigationService, 
			IGithubContributorService githubContributors)
		{
			this.githubContributors = githubContributors;
			_navigationService = navigationService;

			UserIsTypingCommand = new RelayCommand<string>(OnUserSubmitText);

			UserClearedTextCommand = new RelayCommand(OnUserClearedText);

			NavigateToFilterScreenCommand = new RelayCommand(OnNavigateToFilterScreen);
		}
        public MainPageFragmentViewModel(INavigationService navigationService,
                                         IGithubContributorService githubContributors)
        {
            this.githubContributors = githubContributors;
            _navigationService      = navigationService;

            UserIsTypingCommand = new RelayCommand <string>(OnUserSubmitText);

            UserClearedTextCommand = new RelayCommand(OnUserClearedText);

            NavigateToFilterScreenCommand = new RelayCommand(OnNavigateToFilterScreen);
        }
        public AboutViewModel(IGithubContributorService contributorService)
        {
            _contributorService = contributorService;

            Contributors = new ObservableCollection <GithubUser>();
        }
		public AboutViewModel (IGithubContributorService contributorService)
		{
			_contributorService = contributorService;

			Contributors = new ObservableCollection<GithubUser>();
		}