使用Webservice Async DataTable

Question

我不知道为什么这些代码不起作用。我知道webservice有效，因为在一个控制台项目中，它可以工作（使用同步），但是在这里它没有。这是我的代码：

    public interface IService1
    {

        [OperationContract]
        Task<DataTable> GetDataEzra(string command,DataTable tab);
    };

    public async Task GetDataEzra(string command,DataTable tab)
    {
    string ConnectionSQL = "";
        SqlConnection myConnection = new SqlConnection(ConnectionSQL);
        SqlCommand myCommand = new SqlCommand(command, myConnection);
        myCommand.CommandType = CommandType.StoredProcedure;
        myConnection.Open();
        SqlDataAdapter sda = new SqlDataAdapter(myCommand);
        sda.Fill(tab);
        myConnection.Close();
        var task = Task.Factory.StartNew(() => tab);
        return await task;
    }

public Courses()
{
    courses = new ObservableCollection();
    ListView lstView = new ListView();
    DataTable dt = new DataTable();

    var legumes = new ArticleGroupModel() { LongName = "Catégorie Légumes", ShortName = "l" };
    var fruits = new ArticleGroupModel() { LongName = "Catégorie Fruits", ShortName = "f" };
    var task = Task.Factory.StartNew(() => GetResult("GetArticles", dt));
        for (int i = 0; i < dt.Rows.Count; i++)
        {
            fruits.Add(new ArticleModel { Nom = dt.Rows[i][0].ToString(), Type = "Fruit", Image = "tomato.png", Commentaire = "bien frais" });
        }
    courses.Add(legumes);
    courses.Add(fruits);

    lstView.ItemsSource = courses;
    lstView.IsGroupingEnabled = true;
    lstView.GroupDisplayBinding = new Binding("LongName");
    lstView.GroupShortNameBinding = new Binding("ShortName");
    lstView.ItemTemplate = new DataTemplate(typeof(Article));

    Content = new StackLayout
    {
        Children = {
            lstView
        }
    };

}
async static Task GetResult(string command, DataTable tab)
    {
        Service1Client MyClient = new Service1Client();
        var task = Task.Factory.StartNew(() => MyClient.GetDataEzraAsync(command,tab));
        await Task.WhenAny(task, Task.Delay(3500));
    }

你知道吗？我是Xamarin的初学者......编译中没有错误但是就像webservice没有调用一样。

谢谢。