Set Focus to Control

I was trying to set focus using the code

this.ScriptManager1.SetFocus(myControlName.ClientID);

and I wrote this code in my SelectedIndexChanged Event Function. That time this code didn't work.

Now I changed this code to Page Load Function i.e.

protected void Page_Load(object sender, EventArgs e)
{
    if (!IsPostBack)
    {
        this.ScriptManager1.SetFocus(myControlName.ClientID);
    }
    else
    {
        this.ScriptManager1.SetFocus(GetPostBackControl(this.Page).ClientID);
    }
} 

Here I am using a function GetPostBackControl() to identify the current postbacking control and I am setting focus to the same control. If you want to move focus to any other control, just use a Switch Statment.

public static System.Web.UI.Control GetPostBackControl(System.Web.UI.Page page)
{
    Control control = null;
    string ctrlname = page.Request.Params["__EVENTTARGET"];
    if (ctrlname != null && ctrlname != String.Empty)
    {
        control = page.FindControl(ctrlname);
    }
    // if __EVENTTARGET is null, the control is a button type and we need to 
    // iterate over the form collection to find it 
    else
    {
        string ctrlStr = String.Empty;
        Control c = null;
        foreach (string ctl in page.Request.Form)
        {
            // handle ImageButton controls  
            if (ctl.EndsWith(".x") || ctl.EndsWith(".y"))
            {
                ctrlStr = ctl.Substring(0, ctl.Length - 2);
                c = page.FindControl(ctrlStr);
            }
            else
            {
                c = page.FindControl(ctl);
            }
            if (c is System.Web.UI.WebControls.Button ||
            c is System.Web.UI.WebControls.ImageButton)
            {
                control = c;
                break;
            }
        }
    }
    return control;
}