ASP.Net DropDownList OnSelectedIndexChange not firing

Question

I have the following DropDownList control:

Answer 1

AutoPostBack="true" and

write page load event

if (!IsPostBack)
{
   DDL_Designation_Bind();   
}

// Because autopostback properties fire load event then our dropdownlist rebind and always selected index 0 so Not Rebinding dropDownlist