使用uploadvaluesasync处理异常

Question

我想知道如何在此代码中互联网连接离线时处理异常：

private void LoginDialog_myOnLoginComplete(object sender, OnLoginEventArgs e)
    {
        WebClient client = new WebClient();
            Uri uri = new Uri(server);
            NameValueCollection parameters = new NameValueCollection();

            parameters.Add("Email", e.Email);
            parameters.Add("Password", e.Password);
            client.UploadValuesCompleted += Client_UploadValuesCompleted;

            try
            {
                client.UploadValuesAsync(uri, parameters);
            }
            catch (Exception)
            {
            }
     }

 private void Client_UploadValuesCompleted(object sender, UploadValuesCompletedEventArgs e)
    {
        string complete = Encoding.UTF8.GetString(e.Result);
    }

当互联网连接断开时，字符串完成处理异常并且我的应用程序崩溃。我怎么能避免这种情况？