private void button1_Click(object sender, EventArgs e)
        {
            if (downloadTask == null)
            {
                downloadTask = new DownloadTask();
            }

            if (downloadTask.GetState() == DownloadTaskState.Idle)
            {
                downloadTask.Start();
            }
            else
            {
                MyLogger.Attach("Cannot download because state is not " + DownloadTaskState.Idle.ToString() + "." );
            }
        }
        private void button4_Click(object sender, EventArgs e)
        {
            if (downloadTask3 == null)
            {
                downloadTask3 = new DownloadTask();
                downloadTask3.OptionOutputPath("ReferHtmls\\");
                downloadTask3.OptionWordToUrl(word => "http://dictionary.reference.com/browse/" + word);
            }

            if (downloadTask3.GetState() == DownloadTaskState.Idle)
            {
                downloadTask3.Start();
            }
            else
            {
                MyLogger.Attach("Cannot download because state is not " + DownloadTaskState.Idle.ToString() + "." );
            }
        }
        private void button3_Click(object sender, EventArgs e)
        {
            if (downloadTask2 == null)
            {
                downloadTask2 = new DownloadTask();
                downloadTask2.OptionOutputPath("BaiduHtmls\\");
                downloadTask2.OptionWordToUrl(word => "http://dict.baidu.com/s?wd=" + word);
            }

            if (downloadTask2.GetState() == DownloadTaskState.Idle)
            {
                downloadTask2.Start();
            }
            else
            {
                MyLogger.Attach("Cannot download because state is not " + DownloadTaskState.Idle.ToString() + "." );
            }
        }