Async await still blocking the UI in C#

Question

I used following code to execute the SourceCreator method without blocking UI.

string a =null; 
private string SourceCreator()
{
    string sum = textBox7.Text;
    sum = sum.Replace(" ", "+");

    string url = string.Format("https://www.aliexpress.com/wholesale?catId=0&initiative_id=SB_20220824221043&SearchText={0}&spm=a2g0o.productlist.1000002.0", sum);
    HttpWebRequest request = (HttpWebRequest)WebRequest.Create(url);
    HttpWebResponse response = (HttpWebResponse)request.GetResponse();
    StreamReader sr = new StreamReader(response.GetResponseStream());
    // richTextBox2.Text += sr.ReadToEnd();
    a = sr.ReadToEnd();
    sr.Close();

    return a;
}

Here is button click event

private async void Timer4_Tick(object sender, EventArgs e)
{
    Task<string> task1 = new Task<string>(SourceCreator);
    task1.Start();
    string p = await task1;
    textBox10.Text = p;
}

I run this code, but this still blocking my UI of Windows form app. Could somebody tell me why?

Answer 1

You are not actually using any async methods here. You are just passing it to a Task constructor, which is not how you are supposed to do it, and may not work with the WinForms' SynchronizationContext .

HttpWebRequest is effectively deprecated, you should switch to HttpClient instead. And that has a full complement of async methods.

static HttpClient _client = new HttpClient();

private async Task<string> SourceCreator(string sum)
{
    sum = sum.Replace(" ", "+");
    string url = $"https://www.aliexpress.com/wholesale?catId=0&initiative_id=SB_20220824221043&SearchText={sum}&spm=a2g0o.productlist.1000002.0";

    using (var response = await _client.GetAsync(url))
    {
        var a = await response.Content.ReadAsStringAsync();
        return a;
    }
}

private async void Timer4_Tick(object sender, EventArgs e)
{
    string p = await SourceCreator(textBox7.Text);
    textBox10.Text = p;
}