Objective-Cでメソッド定義を差し替えるメソッド

NSObject+Swizzle.h

@interface NSObject(Swizzle)

+ (void)swizzleMethod:(SEL)orig_sel withMethod:(SEL)alt_sel;

@end

NSObject+Swizzle.m

#import "NSObject+Swizzle.h"
#import <objc/objc-class.h>

@implementation NSObject(Swizzle)

+ (void)swizzleMethod:(SEL)orig_sel withMethod:(SEL)alt_sel
{
  Method orig_method = class_getInstanceMethod(self, orig_sel);
  Method alt_method = class_getInstanceMethod(self, alt_sel);

  if (orig_method == nil || alt_method == nil) {
    NSLog(@"method not exists.");
    return;
  }

  class_addMethod(self,
                  orig_sel,
                  class_getMethodImplementation(self, orig_sel),
                  method_getTypeEncoding(orig_method));

  class_addMethod(self,
                  alt_sel,
                  class_getMethodImplementation(self, alt_sel),
                  method_getTypeEncoding(alt_method));

  method_exchangeImplementations(class_getInstanceMethod(self, orig_sel), class_getInstanceMethod(self, alt_sel));
}

@end