c#Coroutine协程 WebClient异步下载静态资源

/// <summary>
        /// 异步下下载静态资源
        /// </summary>
        /// <param name="url"></param>
        /// <returns></returns>
        IEnumerator DownloadFile(string url)
        {
            bool done = false;
            using (var client = new WebClient())
            {
                client.DownloadStringCompleted += (s, e) =>
                {
                    done = true;
                    results.Add(e.Result);
                };
                client.DownloadStringAsync(new Uri(url));
            }
            while (!done)
                yield return null;
        }

        IEnumerator DownloadAllAtOnce()
        {
            //Start multiple async downloads and store their handles
            var downloads = new List<CoroutineHandle>();
            downloads.Add(runner.Run(DownloadFile("http://localhost:1323/static/v3.0.0/1106-1.sql")));
            downloads.Add(runner.Run(DownloadFile("http://localhost:1323/static/v3.0.0/1106-2.sql")));

            //Wait until all downloads are done
            while (downloads.Count > 0)
            {
                yield return null;
                for (int i = 0; i < downloads.Count; ++i)
                    if (!downloads[i].IsRunning)
                        downloads.RemoveAt(i--);
            }
        }

CoroutineRunner runner = new CoroutineRunner();
        const float updateRate = 1f / 30f;
        public void Run2()
        {
            var run = runner.Run(DownloadAllAtOnce());
            while (run.IsRunning)
            {
                runner.Update(updateRate);
            }
        }