How can I change the background after clicking uibutton?

Http://www.cocoachina.com/bbs/read.php? Tid-48666-keyword-UIButton.html

Initial settings:
Uiimage * bgimg1 = [uiimage imagenamed: @ "selected.png"];
Uiimage * bgimg2 = [uiimage imagenamed: @ "unselected.png"];
[BTN setimage: bgimg2 forstate: uicontrolstatenormal];
[BTN setimage: bgimg1 forstate: uicontrolstateselected];

Then, change the button status in the Action Method of the button:
-(Ibaction) buttontouch :( ID) sender
{
Uibutton * button = (Uibutton*) Sender;
Button. Selected =! Button. selected;
}