CSharp: Download Imge

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.IO;
using System.Net;
using System.Net.Http;
using System.Net.Http.Headers;
using System.Data;
using System.Text;
using System.Threading;
using System.Threading.Tasks;
using RestSharp;
using RestSharp.Extensions;
using RestSharp.Authenticators;
using RestSharp.Deserializers;
using RestSharp.Validation;
using Geovin.Du.Commn;

/// <summary>
/// 涂聚文 Geovin Du geovindu
/// 
/// </summary>
public partial class DownloadImge : System.Web.UI.Page
{


    /// <summary>
    /// 
    /// </summary>
    /// <param name="sender"></param>
    /// <param name="e"></param>
    protected void Page_Load(object sender, EventArgs e)
    {

    }
    /// <summary>
    /// 
    /// </summary>
    /// <param name="sender"></param>
    /// <param name="e"></param>
    protected void Button1_Click(object sender, EventArgs e)
    {
        string weburl = this.txtURL.Text.Trim();
        int stat = int.Parse(this.txtStart.Text.Trim());
        int end = int.Parse(this.txtEnd.Text.Trim())+1;
        int k = 0;
        int er = 0;
        for (int i = stat; i< end; i++)
        {
            string fileurl = HttpContext.Current.Server.MapPath(@"ImgFile//" + i.ToString() +this.txtExift.Text.Trim());

            DownloadData(weburl+i.ToString()+this.txtExift.Text.Trim(), fileurl);
            k++;
        }

        Response.Write("Ok" + k.ToString() + ",erro" + er.ToString());

    }
    /// <summary>
    /// 文件下载
    /// </summary>
    /// <param name="website"></param>
    /// <param name="file"></param>
    private async void RunBackground(string website, string file)
    {
        int k = 1;
        int er = 1;
        var succeed = await DownLoadGlobalHistoryNew(website, file);
        if (succeed)
        {
            k++;
        }
        else
        {
            er++;
        }
    }
    /// <summary>
    /// 
    /// </summary>
    /// <param name="errfile"></param>
    /// <returns></returns>
    string geterro(List<string> errfile)
    {
        string str = string.Empty;
        if (errfile.Count > 0)
        {
            int k = 0;
            foreach (string s in errfile)
            {
                if (k == 0)
                {
                    str = s;
                }
                else
                {
                    str = str + "," + s;
                }
                k++;
            }

        }

        return str;
    }
    /// <summary>
    /// 
    /// </summary>
    /// <param name="url"></param>
    /// <param name="file"></param>
    /// <returns></returns>
    public Task<bool> DownLoadGlobalHistoryNew(string url, string file)
    {
        string dataString = string.Empty;

        return Task.Run(() =>
        {
            var succeed = false;
            try
            {
                var dataStringNew = new WebClient { Encoding = Encoding.UTF8 }.DownloadString(url);
                if (dataString != dataStringNew)
                {
                    dataString = dataStringNew;
                    Write(file, dataString);
                    succeed = true;
                }
            }
            catch (Exception)
            {

            }
            return succeed;
        });
    }
    /// <summary>
    /// 
    /// </summary>
    /// <param name="file"></param>
    /// <param name="dataString"></param>
    private void Write(string file, string dataString)
    {
        try
        {
            if (File.Exists(file) && !string.IsNullOrWhiteSpace(dataString))
                File.Delete(file);
            File.WriteAllText(file, dataString);
        }
        catch (Exception)
        {
        }
    }
    /// <summary>
    /// 图片下载
    /// </summary>
    /// <param name="strFileUrlToDownload"></param>
    /// <param name="strfile"></param>
    protected void DownloadData(string strFileUrlToDownload, string strfile)
    {
        WebClient client = new WebClient();
        byte[] myDataBuffer = client.DownloadData(strFileUrlToDownload);

        MemoryStream storeStream = new MemoryStream();

        storeStream.SetLength(myDataBuffer.Length);
        storeStream.Write(myDataBuffer, 0, (int)storeStream.Length);

        storeStream.Flush();

        string currentpath = strfile;// System.IO.Directory.GetCurrentDirectory() + @"\Folder";

        using (FileStream file = new FileStream(currentpath, FileMode.Create, System.IO.FileAccess.ReadWrite))
        {
            byte[] bytes = new byte[storeStream.Length];
            storeStream.Read(bytes, 0, (int)storeStream.Length);
            file.Write(myDataBuffer, 0, (int)storeStream.Length);
            storeStream.Close();
        }

        //The below Getstring method to get data in raw format and manipulate it as per requirement
        string download = Encoding.ASCII.GetString(myDataBuffer);


    }

}