private async Task ExecuteOnGetHistory() { IsBusy = true; if (Selected_MinDate <= Selected_MaxDate) { var _restService = new RESTService(); var Result = await _restService.GetPeriodHistryAsync(Selected_MinDate, Selected_MaxDate); if (Result.Item1) { try { Contacts_List = JsonConvert.DeserializeObject <List <ContactVisiteHistory_Model> >(Result.Item2); var sorted = from contact in Contacts_List orderby contact.DateSort group contact by contact.DateSort into contactGroup select new Grouping <string, ContactVisiteHistory_Model>(contactGroup.Key, contactGroup); Contacts = new ObservableCollection <Grouping <string, ContactVisiteHistory_Model> >(sorted); } catch (Exception e) { DependencyService.Get <IMessage>().ShortAlert(e.Message); } } else { DependencyService.Get <IMessage>().ShortAlert(Result.Item2); } } else { DependencyService.Get <IMessage>().ShortAlert("Erreur Date !"); } IsBusy = false; }