/// <summary>
    /// 增加下载代理辅助器。
    /// </summary>
    /// <param name="index">下载代理辅助器索引。</param>
    private void AddDownloadAgentHelper(int index)
    {
        DownloadAgentHelperBase downloadAgentHelper = new UnityWebRequestDownloadAgentHelper();

        if (downloadAgentHelper == null)
        {
            Debug.LogError("Can not create download agent helper.");
            return;
        }
        m_DownloadManager.AddDownloadAgentHelper(downloadAgentHelper);
    }