public void AddConcertToList ()
 {
     Concert concertToAdd = new Concert(addConcert);
     listConcert.Add(concertToAdd);
 }
        public async Task setAsyncConcertToBD(ObservableCollection<Concert> listConcert)
        {
            foreach (var concert in listConcert)
            {
                Concert newConcert = new Concert(idMusicianToAdd, concert.ConcertAvenir1);

                var urlStringConcert = new Uri("http://webapiphone.azurewebsites.net/api/concertavenirs/InsererConcert");
                HttpClient client = new HttpClient();
                await client.PostAsJsonAsync<Concert>(urlStringConcert,newConcert);
            }
        }