List Box Adding

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ASP.NET

I have one list box in that item having separated by ',' like (It software,Hardware,Banking,accounts) these are all coming from grid view check items and I have one check box when i click on that I want add own items that items also I want to display like ',' (not in next line) I want add items only single line separated by ','

I wrote coding for gridview check box adding in list box with separated by ','

protected void chkcheckquery_CheckedChanged(object sender, EventArgs e)
    {
        
       
        try
        {
            sb = new StringBuilder();
            foreach (GridViewRow gr in gvqueriescheck.Rows)
            {
                if (((CheckBox)gr.FindControl("chkcheckquery")).Checked == true)
                {
                    sb.Append(gr.Cells[1].Text + ",");

                }
            }
            ListBox1.Items.Clear();
            ListBox1.Items.Add(sb.ToString())
        }
        catch (Exception ex)
        {
            lblmessage.Text = ex.Message;
        }

    }

and below gridview I have text box I will enter anything in textbox I want to add in listbox with ','


[Edited]Code is Wrapped in "pre" tag[/Edited]