private async void BtnLogin_OnClicked(object sender, EventArgs e) { string username = CBYear.SelectedItem.ToString() + CBProgram.SelectedItem.ToString() + EntryRollNo.Text.Trim(); BtnLogin.IsEnabled = false; var student = await _studentController .Authenticate( new AuthenticationModel() { Password = entryPassword.Text, Username = username } ); if (student == null) { await DisplayAlert("Unable to login!", "Authentication Error", "Ok"); BtnLogin.IsEnabled = true; return; } Application.Current.MainPage = new NavigationPage(new MainView.MainView()); }