How to check whether the URL is valid or not

I have one textbox in that user enter the URL, but if want to check that URL while page rendering then what to do?

Here is my code:

protected void btnRender_Click(object sender, EventArgs e)
{
    string strResult = string.Empty;
    WebResponse objResponse;
    WebRequest objRequest = System.Net.HttpWebRequest.Create(urltxt.Text);
    objResponse = objRequest.GetResponse();
    using (StreamReader sr = new StreamReader(objResponse.GetResponseStream()))
    {
        strResult = sr.ReadToEnd();
        sr.Close();
    }
    strResult = strResult.Replace("<form id='form1' method='post' action=''>", "");
    strResult = strResult.Replace("</form>", "");          
    TextBox1.Text = strResult.Trim();
    div.InnerHtml = strResult.Trim();
}

I have this code to check whether URL is valid or not, so can you please tell me where to call this?
{if i want to also check https also then how can i do in this code}

 protected bool CheckUrlExists(string url)
    {
        // If the url does not contain Http. Add it.
      // if i want to also check for https how can i do.this code is only for http not https
        if (!url.Contains("http://"))
        {
            url = "http://" + url;
        }
        try
        {
            var request = WebRequest.Create(url) as HttpWebRequest;
            request.Method = "HEAD";
            using (var response = (HttpWebResponse)request.GetResponse())
            {
                return response.StatusCode == HttpStatusCode.OK;
            }
         }
         catch
         {
             return false;
         }
     }

The TextBox name is urltxt

Answers:

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Method 1

Try like below, It will help you….

     protected void btnRender_Click(object sender, EventArgs e)
        {
            if(CheckUrlExists(urltxt.Text))
            {
                string strResult = string.Empty;
                WebResponse objResponse;
                WebRequest objRequest = System.Net.HttpWebRequest.Create(urltxt.Text);
                objResponse = objRequest.GetResponse();
                using (StreamReader sr = new StreamReader(objResponse.GetResponseStream()))
                {
                    strResult = sr.ReadToEnd();
                    sr.Close();
                }
                strResult = strResult.Replace("<form id='form1' method='post' action=''>", "");
                strResult = strResult.Replace("</form>", "");
                TextBox1.Text = strResult.Trim();
                div.InnerHtml = strResult.Trim();
            }
            else
            {
                MessageBox.Show("Not a Valid URL");
            }
        }

Method 2

Try this uriName(your desired URI)

  bool Uriresult = Uri.TryCreate(uriName, UriKind.Absolute, out uriResult) && uriName.Scheme == Uri.UriSchemeHttp;

as per your code

string uriName = urltxt.Text; bool Uriresult = Uri.TryCreate(uriName, UriKind.Absolute, out uriResult) && uriName.Scheme == Uri.UriSchemeHttp;

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