[iOS SDK] override methods in runtime (Swizzling)

gistfile1.m

/*
    Category implementation
*/

#import "UIViewController+Swizzle.h"
#import <objc/runtime.h>

@implementation UIViewController (Swizzle)

+ (void)load
{
    Method original_appear, swizzle_appear, original_disappear, swizzle_disappear;
    
    original_appear = class_getInstanceMethod(self, @selector(viewWillAppear:));
    swizzle_appear = class_getInstanceMethod(self, @selector(viewWillAppearExtended:));
    
    original_disappear = class_getInstanceMethod(self, @selector(viewWillDisappear:));
    swizzle_disappear = class_getInstanceMethod(self, @selector(viewWillDisappearExtended:));
    
    method_exchangeImplementations(original_appear, swizzle_appear);
    method_exchangeImplementations(original_disappear, swizzle_disappear);
}

- (void)viewWillAppearExtended:(BOOL)animated
{
    NSLog(@"\n===\n\nView will appear\n\n===\n");
    return [self viewWillAppearExtended:animated];
}

- (void)viewWillDisappearExtended:(BOOL)animated
{
    NSLog(@"\n===\n\nView will disappear\n\n===\n");
    return [self viewWillDisappearExtended:animated];
}

@end