WebService 异步调用

 protected void Page_Load(object sender, EventArgs e)
    {
        Service service = new localhost.Service();
        service.HelloWorldCompleted += new HelloWorldCompletedEventHandler(callback);
        service.HelloWorldAsync();
     }

    public void callback(object sender, HelloWorldCompletedEventArgs e)
    {
        if (e.Error == null)
        {
            Response.Write(e.Result);
            //Label1.Text = e.Result;

        }
        else
        {
            Response.Write(e.Error.Message);
        }
    }