DownloadFileCompleted事件在循环c#.net时不会在内部触发

它自己下载的文件非常好。

谢谢任何人能给我的帮助

class DownloadQueue
{
    public List<string[]> DownloadItems { get; set; }
    public int CurrentDownloads;
    public int DownloadInProgress;
    string url = @"http://www.google.co.uk/intl/en_uk/images/logo.gif";
    bool downloadComplete;

    public DownloadQueue()
    {
        CurrentDownloads = 0;
        DownloadItems = new List<string[]>();
        Console.Write("new download queue made");
    }

    public void startDownloading(int maxSimulatiousDownloads)
    {
        downloadComplete = true;
        DownloadInProgress = 0;
        WebClient client = new WebClient();
        client.DownloadFileCompleted +=
                    new AsyncCompletedEventHandler(this.downloadCompleteMethod);


            while(DownloadInProgress != DownloadItems.Count )
            {
                if (downloadComplete == true)
                {
                    downloadComplete = false;          

                    client.DownloadFileAsync(new Uri(DownloadItems.ElementAt(DownloadInProgress).ElementAt(0).ToString()), DownloadItems.ElementAt(DownloadInProgress).ElementAt(1).ToString());                        
                }
            }
        Console.Write("all downloads completed");
    }

    private void downloadCompleteMethod(object sender, AsyncCompletedEventArgs e)
    {            
        downloadComplete = true;
        DownloadInProgress++;
        Console.Write("file Downloaded");
    }

    }