Question

My controls are dynamically generated when the dropdownlist is changed by user. They values are loaded from the database. How to display progressbar during the generation of control?

Answer 1

You can add download image on the form. When user will change item in dropdownlist call the event onchange with javascript. There is example for adding handler:

protected void Page_Load(object sender, EventArgs e)
        {
           dropdownlist1.Attributes.Add("onchange", "document.getElementById(\"loading_image\").style.visibility = \"visible\";");
        }

Before that you must add image on the form:

<img style="visibility:hidden;" src="imageurl" runat="server" id="loading_image" />