Issue with passing a variable through prepareForSegue method

I am getting an error that I can't seem to solve:

    *** Terminating app due to uncaught exception 'NSInvalidArgumentException',
 reason: '-[UICollectionViewController setSearchString:]: unrecognized 
selector sent to instance 0x7fcd4b655930'

The error comes when I call a prepareForSegue method:

- (void) prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender
{

    NSString *searchStringToPass = [[NSString alloc]initWithFormat:_inputField.text];
    UINavigationController *navController = [segue destinationViewController];
    ResultsCollectionViewController *rvc = (ResultsCollectionViewController *)([navController viewControllers][0]);
    NSLog(@"Search String to Pass is: %@", searchStringToPass);
    //[rvc setSearchString:searchStringToPass];
    rvc.searchString = searchStringToPass;
        //userViewController.user = [self.users objectInListAtIndex:[self.tableView indexPathForSelectedRow].row];

}

The ViewController that I am trying to get to is imbedded in a navigation controller. The code for it is:

#import "ResultsCollectionViewController.h"

@interface ResultsCollectionViewController ()
//@property(nonatomic, weak) IBOutlet UICollectionView *collectionView;
@property(strong, nonatomic) NSArray *flickrPhotos;


@end

@implementation ResultsCollectionViewController

- (void)viewDidLoad {
    [super viewDidLoad];
    // Do any additional setup after loading the view.
    NSLog(@"search string is %@",_searchString);
}

-(void)getFlickrPhotosWithSearchString:(NSString*)searchString{


}

- (void)didReceiveMemoryWarning {
    [super didReceiveMemoryWarning];
    // Dispose of any resources that can be recreated.
}

And the .h file is:

#import "BaseViewController.h"

@interface ResultsCollectionViewController : BaseViewController <UICollectionViewDataSource, UICollectionViewDelegateFlowLayout>
@property (strong, nonatomic) NSString *searchString;



@end

Anybody have any idea what the issue is? Many thanks in advance.