UIViewController+Swizzled.m

@implementation UIViewController (Swizzled)

+ (void)load
{
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        
        [self swizzlingInstanceMethod:@selector(viewDidLoad) swizzledSelector:@selector(swizzled_viewDidLoad)];
    });
}

#pragma mark - Method Swizzling

+ (void)swizzlingInstanceMethod:(SEL)originalSelector swizzledSelector:(SEL)swizzledSelector
{
    Class class = [self class];
    [self swizzlingMethod:originalSelector swizzledSelector:swizzledSelector forClass:class];
}


+ (void)swizzlingClassMethod:(SEL)originalSelector swizzledSelector:(SEL)swizzledSelector
{
    Class class = object_getClass((id)self);
    [self swizzlingMethod:originalSelector swizzledSelector:swizzledSelector forClass:class];
}

+ (void)swizzlingMethod:(SEL)originalSelector swizzledSelector:(SEL)swizzledSelector forClass:(Class)class
{
    Method originalMethod = class_getInstanceMethod(class, originalSelector);
    Method swizzledMethod = class_getInstanceMethod(class, swizzledSelector);
    
    BOOL didAddMethod =
    class_addMethod(class,
                    originalSelector,
                    method_getImplementation(swizzledMethod),
                    method_getTypeEncoding(swizzledMethod));
    
    if (didAddMethod) {
        class_replaceMethod(class,
                            swizzledSelector,
                            method_getImplementation(originalMethod),
                            method_getTypeEncoding(originalMethod));
    } else {
        method_exchangeImplementations(originalMethod, swizzledMethod);
    }
    
}


#pragma mark - Swizzled methods

- (void)swizzled_viewDidLoad
{
    [self swizzled_viewDidLoad];
}

@end