Synchronous WebClient

Question

I have a calculator application that performs various download functions to get values for the calculations. I paid someone to develop this for me and the developer is now history. Recently I discovered an error message when the application is run concurrently. "WebClient does not support concurrent I/O operations."

I am not a developer, but I understand the gist of what's happening. Either I need to use an asynchronous WebClient method or find a way to schedule the synchronous process better.

I copied a snippet of the code from my .cs file. Altogether there are 5 instances of the WebClient "client". I copied one of those for space sake.

My question is how would I code this asynchronously or is there a way to pause a synchronous instance of WebClient until previous instances are completed? I don't mind the delay, I just don't want the error message to pop up for the end user. Thanks to anyone who can help.

Code Snippet:

using System;
using System.Data;
using System.Data.OleDb;
using System.Configuration;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.HtmlControls;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Net;
using System.IO;
using System.Xml;
using System.Text;
using System.Text.RegularExpressions;
using proquest.Data;
using proquest.Entities;

public static WebClient client = new WebClient();

    #endregion

///<Comment>There is unrelated code here. I skipped until next instance of WebClient///</Comment>

public static double TreasuryValue(RateType type)
    {
        string xmlurl = "http://www.ustreas.gov/offices/domestic-finance/debt-management/interest-rate/yield.xml";

        string filepath = HttpContext.Current.Server.MapPath("~/documents/yeild.xml");

        if (File.Exists(filepath) && hoursSinceLastUpdate(filepath) > 24)
        {
            try
            {
                client.DownloadFile(xmlurl, filepath);
            }
            catch
            {
            }
        }
        else if (!File.Exists(filepath))
        {
            try
            {
                client.DownloadFile(xmlurl, filepath);
            }
            catch
            {
            }
        }

Rodick Wu · Answer

And I am afraid it's not enough Maybe you need change the method to multi-threading in any case you can try to add Async=true first

Rodick Wu · Answer

oh It don't allow execute asynchronous operations in webform(B/S system) try to add a sentence at the top of page. Async=true Such as :

joe bloe · Answer

Sorry Roddick. I tried posting again but it didn't take. I left out a ). Forget my last post. Your instructions seemed to work but I did get another error message. Asynchronous operations are not allowed in this context. Page starting an asynchronous operation has to have the Async attribute set to true and an asynchronous operation can only be started on a page prior to PreRenderComplete event. Let me know what you think about this. Thanks again for your help. I am in a realy jam on this one.

Rodick Wu · Answer

It's strangeIt's build success here the first argument is a Uri objectand the second argument is object type you can try to run the code as below: WebClient client = new WebClient(); string xmlurl=http://www.ustreas.gov/offices/domestic-finance/debt-management/interest-rate/yield.xml; string filepath =HttpContext.Current.Server.MapPath(~/documents/yeild.xml); Uri uri = new Uri(xmlurl); client.DownloadDataAsync(uri filepath);

joe bloe · Answer

Thanks for responding. I tried that and I got 2 errors that said 1. The best overloaded method match for 'System.Net.WebClient.DownloadDataAsync(System.Uri object)' has some invalid arguments 2. Argument '1': cannot convert from 'string' to 'System.Uri' I guess I need to make a Uri object? How is that different than the string filepath?

Rodick Wu · Answer

try this: replace the current method as below: client.DownloadFile(xmlurl filepath); ==> client.DownloadDataAsync(new Uri(xmlurl) filepath);