set cornerRadius of class using UIButton appearanceWhenContainedIn

set cornerRadius of class using UIButton appearanceWhenContainedIn

so far I have changed image of all the button which are in my class by
using following code
[[UIButton appearanceWhenContainedIn:[FirstPadViewController class],
nil] setBackgroundImage:img forState:UIControlStateNormal];
as I dont want to create outlet thats why I have used this way so how can
I set cornerRadius using UIButton appearanceWhenContainedIn
any help will really decrease amount of code I will write thank you