Swizzling.

NSObject+Swizzling.h

#import <Foundation/Foundation.h>

@interface NSObject (Swizzling)

- (void)swizzleMethod:(SEL)originalSelector toMethod:(SEL)newSelector;

@end

NSObject+Swizzling.m

#import <objc/runtime.h>

@implementation NSObject (Swizzling)

- (void)swizzleMethod:(SEL)originalSelector toMethod:(SEL)newSelector {
    Method origMethod = class_getInstanceMethod(self.class, originalSelector);
    Method newMethod = class_getInstanceMethod(self.class, newSelector);
    if(class_addMethod(self.class, originalSelector, method_getImplementation(newMethod), method_getTypeEncoding(newMethod))) {
        class_replaceMethod(self.class, newSelector, method_getImplementation(origMethod), method_getTypeEncoding(origMethod));
    } else {
        method_exchangeImplementations(origMethod, newMethod);
    }
}

@end