private void btnOK_Click(object sender, EventArgs e)
    {
        if (txtItemURL.Text.StartsWith("https://steamcommunity.com/market/listings/730/") == true)
        {
            Helpers.Helper.BuildURL(txtItemURL.Text);

            SteamMarketItem SMI = Helpers.Helper.GetItemDetails();
            lblPrice.Text = SMI.LowestPrice.ToString()   "$";
            pbItemImage.ImageLocation = SMI.ImagePath;

            Helpers.Helper.Kontrollar_BerpaEt();
        }
        else
        {
            Helpers.Helper.Kontrollar_SifirlaYanlisDaxilEdilib();
        }
    }

Method GetItemDetails():

    public static SteamMarketItem GetItemDetails()
    {
        WinForms.Control.CheckForIllegalCrossThreadCalls = false;

        Task.Run(() =>
        {
            try
            {
                using (HttpClient client = new HttpClient())
                {
                    JavaScriptSerializer serializer = new JavaScriptSerializer();

                    /* Get item info: */
                    var ResultFromEndpoint1 = client.GetAsync(ReadyEndpointURL1).Result;
                    var Json1 = ResultFromEndpoint1.Content.ReadAsStringAsync().Result;
                    dynamic item = serializer.Deserialize<object>(Json1);
                    marketItem.LowestPrice = float.Parse(((string)item["lowest_price"]).Replace("$", "").Replace(".", ","));

                    /* Get item image: */
                    var ResultFromEndpoint2 = client.GetAsync(ReadyEndPointURL2).Result;
                    var Json2 = ResultFromEndpoint2.Content.ReadAsStringAsync().Result;
                    var html = ((dynamic)serializer.Deserialize<object>(Json2))["results_html"];

                    HtmlDocument htmlDoc = new HtmlDocument();
                    htmlDoc.LoadHtml(html);
                    marketItem.ImagePath = htmlDoc.DocumentNode.SelectSingleNode("//img[@class='market_listing_item_img']").Attributes["src"].Value   ".png";

                    Kontrollar_BerpaEt();
                }
            }
            catch
            {
                Kontrollar_SifirlaYanlisDaxilEdilib();
            }
        });

        return marketItem;
    }

Class SteamMarketItem:

public class SteamMarketItem
{
    public string ImagePath { get; set; }
    public float LowestPrice { get; set; }
}

When im using Task.Run() first click not working, without Task.Run() working but main UI thread stopping when request not finished.

I have no idea why this happens, I cant find problem fix myself, I will be glad to get help from you. Thanks.

CodePudding user response：

If you want to use async you need to change your event handler to async so you can use await, please see the following:

1. Change your Event handler to async void, async void is acceptable on event handler methods, you should try to use async Task in place of async void in most other cases, so change your method signature to the following:

   private async void btnOK_Click(object sender, EventArgs e)
   {
        if (txtItemURL.Text.StartsWith("https://steamcommunity.com/market/listings/730/") == true)
        {
            Helpers.Helper.BuildURL(txtItemURL.Text);
            //here we use await to await the task   
            SteamMarketItem SMI = await Helpers.Helper.GetItemDetails();
            lblPrice.Text = SMI.LowestPrice.ToString()   "$";
            pbItemImage.ImageLocation = SMI.ImagePath;

            Helpers.Helper.Kontrollar_BerpaEt();
        }
        else
        {
            Helpers.Helper.Kontrollar_SifirlaYanlisDaxilEdilib();
        }
   }

2. You shouldn't need to use Task.Run, HttpClient exposes async methods and you can make the method async, also, calling .Result to block on an async method is typically not a good idea and you should make the enclosing method async so you can utilize await:

   //Change signature to async and return a Task<T>
   public async static Task<SteamMarketItem> GetItemDetails()
   {
       WinForms.Control.CheckForIllegalCrossThreadCalls = false;
       //what is marketItem?? Where is it declared?
       try
       {
           using (HttpClient client = new HttpClient())
           {
               JavaScriptSerializer serializer = new JavaScriptSerializer();

                /* Get item info: */
                var ResultFromEndpoint1 = await client.GetAsync(ReadyEndpointURL1);
                var Json1 = await ResultFromEndpoint1.Content.ReadAsStringAsync();
                dynamic item = serializer.Deserialize<object>(Json1);
                marketItem.LowestPrice = float.Parse(((string)item["lowest_price"]).Replace("$", "").Replace(".", ","));

                /* Get item image: */
                var ResultFromEndpoint2 = await client.GetAsync(ReadyEndPointURL2);
                var Json2 = await ResultFromEndpoint2.Content.ReadAsStringAsync();
                var html = ((dynamic)serializer.Deserialize<object>(Json2))["results_html"];

                HtmlDocument htmlDoc = new HtmlDocument();
                htmlDoc.LoadHtml(html);
                marketItem.ImagePath = htmlDoc.DocumentNode.SelectSingleNode("//img[@class='market_listing_item_img']").Attributes["src"].Value   ".png";

                Kontrollar_BerpaEt();
           }
       }
       catch
       {
            Kontrollar_SifirlaYanlisDaxilEdilib();
       }
       //what is marketItem?? Where is it declared?
       return marketItem;
   }