change selecteditem of dropdownlist after binding

[kaine]

i have a droplist in page that i bind this with code\[code\] Category catObj = new Category(); dropCat.DataSource = catObj.GetAllCategory(); dropCat.DataTextField = "Title"; dropCat.DataValueField = "CategoryID"; dropCat.DataBind();\[/code\]i want change selected item of droplist with ths code\[code\]dropCat.SelectedIndex = Convert.ToInt32(catObj.ParentId);\[/code\]but this code cant change the selected itemplease help me thank you all