Method swizzling via category

gistfile1.m

SEL originalSelector = @selector(userInterfaceIdiom);
SEL swizzledSelector = @selector(padUserInterfaceIdiom);
            
Method originalMethod = class_getInstanceMethod([UIDevice class], originalSelector);
Method swizzledMethod = class_getInstanceMethod([UIDevice class], swizzledSelector);
            
BOOL didAddMethod =
class_addMethod([UIDevice class],
            originalSelector,
            method_getImplementation(swizzledMethod),
            method_getTypeEncoding(swizzledMethod));
            
if (didAddMethod) {
            class_replaceMethod([UIDevice class],
                        swizzledSelector,
                        method_getImplementation(originalMethod),
                        method_getTypeEncoding(originalMethod));
}
else {
            method_exchangeImplementations(originalMethod, swizzledMethod);
}