App crashes when passing data from one ViewController to another

I'm attempting to pass the string in the itemSearch text field from my SearchViewController to my CriteriaViewController. I have everything setup according to this thread: Passing Data between View Controllers. The only difference is that rather than passing a BOOL, I'm passing a string. I think my error is how I'm handling this part: controller.itemSearch == self.itemSearch.text;

Error message:

-[CriteriaViewController topViewController]: unrecognized selector sent to instance 0xa99df90
2014-04-17 17:54:20.534 Parse+Storyboard[7095:60b] *** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason:'-[CriteriaViewController topViewController]: unrecognized selector sent to instance 0xa99df90'
*** First throw call stack:
(
    0   CoreFoundation                      0x02a751e4 __exceptionPreprocess + 180
    1   libobjc.A.dylib                     0x026338e5 objc_exception_throw + 44
    2   CoreFoundation                      0x02b12243 -[NSObject(NSObject) doesNotRecognizeSelector:] + 275
    3   CoreFoundation                      0x02a6550b ___forwarding___ + 1019
    4   CoreFoundation                      0x02a650ee _CF_forwarding_prep_0 + 14
    5   Parse+Storyboard                    0x0000348e -[SearchViewController prepareForSegue:sender:] + 238
    6   UIKit                               0x01857efa -[UIStoryboardSegueTemplate _perform:] + 156
    7   UIKit                               0x0141441c -[UIViewController performSegueWithIdentifier:sender:] + 72
    8   Parse+Storyboard                    0x000032d1 __35-[SearchViewController nextButton:]_block_invoke + 257
    9   Parse+Storyboard                    0x0007a087 __40-[PFTask thenCallBackOnMainThreadAsync:]_block_invoke_2 + 241
    10  libdispatch.dylib                   0x036857b8 _dispatch_call_block_and_release + 15
    11  libdispatch.dylib                   0x0369a4d0 _dispatch_client_callout + 14
    12  libdispatch.dylib                   0x03688726 _dispatch_main_queue_callback_4CF + 340
    13  CoreFoundation                      0x02ada43e __CFRUNLOOP_IS_SERVICING_THE_MAIN_DISPATCH_QUEUE__ + 14
    14  CoreFoundation                      0x02a1b5cb __CFRunLoopRun + 1963
    15  CoreFoundation                      0x02a1a9d3 CFRunLoopRunSpecific + 467
    16  CoreFoundation                      0x02a1a7eb CFRunLoopRunInMode + 123
    17  GraphicsServices                    0x02cd25ee GSEventRunModal + 192
    18  GraphicsServices                    0x02cd242b GSEventRun + 104
    19  UIKit                               0x012f3f9b UIApplicationMain + 1225
    20  Parse+Storyboard                    0x000028ad main + 141
    21  libdyld.dylib                       0x038cf701 start + 1
)
libc++abi.dylib: terminating with uncaught exception of type NSException

SearchViewController.h:

#import <UIKit/UIKit.h>
#import <Parse/Parse.h>
#import <Parse/PFCloud.h>
#import "CriteriaViewController.h"


@interface SearchViewController : UIViewController

@property (weak, nonatomic) IBOutlet UIButton *nextButtonOutlet;

@end

SearchViewController.m:

- (void)prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender
{
    if([segue.identifier isEqualToString:@"ShowCriteriaSegue"]){
        UINavigationController *navController = (UINavigationController *)segue.destinationViewController;
        CriteriaViewController *controller = (CriteriaViewController *)navController.topViewController;
        controller.itemSearch == self.itemSearch.text;
        }


}

CriteriaViewController.h

#import <UIKit/UIKit.h>
#import <Parse/Parse.h>

@interface CriteriaViewController : UIViewController

@property (nonatomic) IBOutlet UITextField *itemSearch;

@end

This line:

controller.itemSearch == self.itemSearch.text;

== is for comparison not assignment, replace it with just one equal sign.