setImage forState方法设置按钮上所有状态的图像

I have this small problem that i cannot figure out. I have about 16 buttons and they are connected as an outlet collection to my controller.And also they have an action method which makes the buttons change their state from default to selected. Im trying to change all the buttons' images for only default state. So i run a loop through the array and set their image for the default state using setImage: forState: method. However the method changes the images for all states( Default and selected states ).I have this small problem that i cannot figure