private async Task <bool> ValidateForm(Models.Models.Client client)
        {
            if (client.Firstname == null || client.Lastname == null)
            {
                var dialog = new MessageDialog("Veuillez indiquer les champs obligatoires !");
                await dialog.ShowAsync();

                return(true);
            }

            return(false);
        }
        private async void ContentDialog_PrimaryButtonClick(ContentDialog sender, ContentDialogButtonClickEventArgs args)
        {
            var deferral = args.GetDeferral();

            Models.Models.Client client = new Models.Models.Client
            {
                Firstname = (Firstname.Text != "") ? Firstname.Text : null,
                Lastname  = (Lastname.Text != "") ? Lastname.Text : null,
                Phone     = (Phone.Text != "") ? Phone.Text : null,
                Email     = (Email.Text != "") ? Email.Text : null,
            };

            args.Cancel = await ValidateForm(client);

            if (!args.Cancel)
            {
                bool Response = await RestClient.Instance.Post <Models.Models.Client>(client);
            }

            deferral.Complete();
        }