Get control name in Page_Load event which make the post back

Need to know which specific control posted back to your page? (Original article at http://geekswithblogs.net/mahesh/archive/2006/06/27/83264.aspx)
/// <summary>
/// Gets the ID of the post back control.
/// </summary>
/// <param name = "page">The page.</param>
/// <returns></returns>
public static string GetPostBackControlId(this Page page)
{
    if (!page.IsPostBack)
        return string.Empty;
    Control control = null;
    // first we will check the "__EVENTTARGET" because if post back made by the controls
    // which used "_doPostBack" function also available in Request.Form collection.
    string controlName = page.Request.Params["__EVENTTARGET"];
    if (!String.IsNullOrEmpty(controlName))
    {
        control = page.FindControl(controlName);
    }
    else
    {
        // if __EVENTTARGET is null, the control is a button type and we need to
        // iterate over the form collection to find it
        // ReSharper disable TooWideLocalVariableScope
        string controlId;
        Control foundControl;
        // ReSharper restore TooWideLocalVariableScope
        foreach (string ctl in page.Request.Form)
        {
            // handle ImageButton they having an additional "quasi-property" 
            // in their Id which identifies mouse x and y coordinates
            if (ctl.EndsWith(".x") || ctl.EndsWith(".y"))
            {
                controlId = ctl.Substring(0, ctl.Length - 2);
                foundControl = page.FindControl(controlId);
            }
            else
            {
                foundControl = page.FindControl(ctl);
            }


            if (!(foundControl is Button || foundControl is ImageButton)) continue;


            control = foundControl;
            break;
        }
    }
    return control == null ? String.Empty : control.ID;
}


If you are using master pages, simply add this to the master.cs file and where you need to call the method use the following code:
MasterPage masterPage = (MasterPage)Page.Master; // where MasterPage is the class name
 Control rep = masterPage.getPostBackControlName();
 if (rep.Parent.Parent.ID == "rpRegion")// only if postback is the regions control
 GetSelectedRegion();