winform通过webclient下载文件后打开

        void runFile(SharedFile r)
        {
            var filepath = Path.Combine(Application.StartupPath, "Doc", r.FileName);
            if (File.Exists(filepath))
            {
                if (r.Viewed)
                {
                    System.Diagnostics.Process.Start(filepath);
                    return;
                }
                else
                {
                    File.Delete(filepath);
                }
            }
            dgSharedFile.Enabled = false;
            waitingFilePanel.Visible = true;
            this.Cursor = Cursors.WaitCursor;
            wc = new WebClient();
            wc.DownloadFileCompleted += new AsyncCompletedEventHandler(wc_DownloadFileCompleted);
            try
            {
                var url = string.Format("{0}files/Doc/{1}.{2}",
                    ServiceAgent.GetServiceUrl(),
                    r.Id,
                    r.FileName.Split('.').LastOrDefault());
                var uri = new Uri(url);
                wc.DownloadFileAsync(uri, filepath, r);
            }
            catch
            {
                Program.Alert("此文件正在被另一个进程所使用，请先关闭使用该文件的进程");
            }
        }

        void wc_DownloadFileCompleted(object sender, AsyncCompletedEventArgs e)
        {
            var r = e.UserState as SharedFile;
            var filepath = Path.Combine(Application.StartupPath, "Doc", r.FileName);
            dgSharedFile.Enabled = true;
            waitingFilePanel.Visible = false;
            this.Cursor = Cursors.Default;

            if (e.Cancelled)
            {
                if (File.Exists(filepath))
                {
                    File.Delete(filepath);
                }
            }
            else
            {
                try
                {
                    System.Diagnostics.Process.Start(filepath);
                    if (!r.Viewed)
                    {
                        ServiceAgent.ViewSharedFile(r.Id);
                        UpdateSharedFile();
                    }
                }
                catch
                {
                    Program.Alert("文件打开失败");
                }
            }
        }