public AllLecturers() { InitializeComponent(); LecturerList.BindingContext = lecturerViewModel; var sortTapGestureRecognizer = new TapGestureRecognizer(); sortTapGestureRecognizer.Tapped += (s, e) => { if (currentSort == 1) { currentSort = 2; //z-a SortIcon.Source = "azup.png"; lecturerViewModel = new LecturerViewModel(lecturerViewModel.SortZA()); LecturerList.BindingContext = lecturerViewModel; } else if (currentSort == 2) { currentSort = 3; //5-0 SortIcon.Source = "stardown.png"; lecturerViewModel = new LecturerViewModel(lecturerViewModel.Sort50()); LecturerList.BindingContext = lecturerViewModel; } else if (currentSort == 3) { currentSort = 4; //0-5 SortIcon.Source = "starup.png"; lecturerViewModel = new LecturerViewModel(lecturerViewModel.Sort05()); LecturerList.BindingContext = lecturerViewModel; } else { currentSort = 1; //a-z SortIcon.Source = "azdown.png"; lecturerViewModel = new LecturerViewModel(lecturerViewModel.SortAZ()); LecturerList.BindingContext = lecturerViewModel; } }; SortIcon.GestureRecognizers.Add(sortTapGestureRecognizer); }