Method Swizzling

gistfile1.m

// json file
{
	"Accounts":[{
              "AccountNumber":"String content",
              "Address":{
              "Address1":"String content",
              "Address2":"String content",
              "City":"String content",
              "State":"String content",
              "ZipCode":"String content"
              }],
	"UniqueID":"String content",
	"UserToken":"String content"
}

// utility method 

void SwapMethods(Class aClass, SEL orig_sel, SEL alt_sel, BOOL forInstance) {

  if (aClass != nil) {

    Method orig_method = nil, alt_method = nil;

    if (forInstance) {

      orig_method = class_getInstanceMethod(aClass, orig_sel);
      alt_method = class_getInstanceMethod(aClass, alt_sel);

    } else {

      orig_method = class_getClassMethod(aClass, orig_sel);
      alt_method = class_getClassMethod(aClass, alt_sel);
    }
    // If both are found, swizzle them
    if ((orig_method != nil) && (alt_method != nil)) {

      method_exchangeImplementations(orig_method, alt_method);

    } else {

      NSLog(@"SwapMethods Error: Original %@, Alternate %@",
            (orig_method == nil)?@" not found":@" found",
            (alt_method == nil)?@" not found":@" found");
    }

  } else {

    NSLog(@"SwapMethods Error: Class not found");
  }
}

void SwapMethodsForDifferentClass(Class aClassSwappedTo, SEL orig_sel, Class aClassSwappedFrom, SEL alt_sel, BOOL forInstance) {

  if (aClassSwappedTo != nil) {

    Method orig_method = nil, alt_method = nil;

    if (forInstance) {

      orig_method = class_getInstanceMethod(aClassSwappedTo, orig_sel);
      alt_method = class_getInstanceMethod(aClassSwappedFrom, alt_sel);

    } else {

      orig_method = class_getClassMethod(aClassSwappedTo, orig_sel);
      alt_method = class_getClassMethod(aClassSwappedFrom, alt_sel);
    }
    // If both are found, swizzle them
    if ((orig_method != nil) && (alt_method != nil)) {

      method_exchangeImplementations(orig_method, alt_method);

    } else {

      NSLog(@"SwapMethods Error: Original %@, Alternate %@",
            (orig_method == nil) ? @" not found" : @" found",
            (alt_method == nil) ? @" not found" : @" found");
    }
  } else {

    NSLog(@"SwapMethods Error: Class not found");
  }
}

/**
 * Class extension: CWExtensions
 * Overriding load so that I can swap out 3rd party framework methods
 * for my own
 */

#import <ThirdPartyFramework/ThirdPartyFramework>
#import "MockDataManager.h"
#import <objc/runtime.h>
#import <objc/message.h>

@interface ThirdPartyFramework (CWExtensions)

@end

#import "ThirdPartyFramework+CWExtensions.h"

@implementation ThirdPartyFramework (CWExtensions)

+ (void)load {
#if USEMOCKOBJECTS
  SwapMethodsForDifferentClass([self class], @selector(logInWithUserName:password:), [MockDataManager class], @selector(loadLoginResponse), YES);
#endif
}

@end

// MockDataManager
@interface MockDataManager : NSObject

+ (MockDataManager *)sharedManager;
- (LoginResponse *)loadLoginResponse;
@end

static NSString* const loginResponseFile = @"LoginResponse";
static char const *fileQueueName         = "com.corywiles.file.handler.queue";
static dispatch_queue_t _fileQueue;

@implementation EPBMockDataManager

static MockDataManager *shared = nil;

+ (void)initialize {
  _fileQueue = dispatch_queue_create(fileQueueName, 0);
}

+ (MockDataManager *)sharedManager {

  static dispatch_once_t pred;

  dispatch_once(&pred, ^{
    shared = [[EPBMockDataManager alloc] init];
  });


  return shared;
}

- (id)init {

  self = [super init];

  if (self) {

  }

  return self;
}

- (LoginResponse *)loadLoginResponse {

  __block LoginResponse *__obj  = nil;

  if (__obj == nil) {

    __block NSData *jsonData;
    __block NSDictionary *objDictionary = @{};

    NSString *path  = [[NSBundle mainBundle] pathForResource:loginResponseFile ofType:@"json"];
    BOOL fileExists = [[NSFileManager defaultManager] fileExistsAtPath:path];

    NSAssert(fileExists, @"The path for %@ must exist", loginResponseFile);

    dispatch_async(_fileQueue, ^{

      jsonData      = [NSData dataWithContentsOfFile:path];
      objDictionary = [NSDictionary dictionaryJSONFromData:jsonData];
    });

    dispatch_sync(_fileQueue, ^{
      __obj = [[LoginResponse alloc] initWithJSONDictionary:objDictionary];
    });

    if (!__obj) {

      return nil;
    }
  }

  return __obj;
}

@end

// view controller that has vendors code
// if you set the preprocessor then swizzle method is called
// no need to if/else to use your test method

  ThirdPartyFramework *ws = [ThirdPartyFramework sharedManager];

  LoginResponse *loginResponse = [ws logInWithUserName:@"xxxx" password:@"xxxx"];

  EPBLog(@"loginResponse: %@", loginResponse);