Я хотел бы реализовать поэтапный поиск слов. Я реализовал, как показано ниже, но методы filterContentForSearchText и shouldReloadTableForSearchString не вызываются. Почему?

WordsIndexViewController.h

#import <UIKit/UIKit.h>

@interface WordsIndexViewController : UIViewController <UITableViewDataSource, UITableViewDelegate, UISearchDisplayDelegate, UISearchBarDelegate>

@end

WordsIndexViewController.m

#import "WordsIndexViewController.h"
#import "WordsShowViewController.h"
#import "Word.h"

@interface WordsIndexViewController ()

@property (strong, nonatomic) UITableView *tableView;

@property (strong, nonatomic) NSArray *words;
@property (strong, nonatomic) NSMutableArray *searchedWords;

@end

@implementation WordsIndexViewController

- (id)initWithNibName:(NSString *)nibNameOrNil bundle:(NSBundle *)nibBundleOrNil
{
    self = [super initWithNibName:nibNameOrNil bundle:nibBundleOrNil];
    if (self) {
        // Custom initialization
    }
    return self;
}

- (void)viewDidLoad
{
    [super viewDidLoad];
    // Do any additional setup after loading the view.

    _words = [[app models] objectForKey:@"words"];
    _searchedWords = [NSMutableArray arrayWithArray:@[]];

    UITableView *tableView = [[UITableView alloc] initWithFrame:CGRectMake(0, 0, 320, 480) style:UITableViewStylePlain];
    tableView.delegate = self;
    tableView.dataSource = self;
    _tableView = tableView;

    UISearchBar *searchBar = [[UISearchBar alloc] initWithFrame:CGRectMake(0, 0, self.view.bounds.size.width, 44)];
    searchBar.delegate = self; // needed?
    [searchBar sizeToFit]; // needed?

    UISearchDisplayController *searchDisplayController = [[UISearchDisplayController alloc] initWithSearchBar:searchBar contentsController:self];
    searchDisplayController.delegate = self;
    searchDisplayController.searchResultsDelegate = self;
    searchDisplayController.searchResultsDataSource = self;
    _tableView.tableHeaderView = searchBar;

    [self.view addSubview:_tableView];
}

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

#pragma mark - related to UITableView
- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section {
    NSLog(@"START numberOfRowsInSection");

    NSArray *words = nil;
    if (tableView == self.searchDisplayController.searchResultsTableView) {
        words = _searchedWords;
    } else {
        words = _words;
    }

    return [words count];
}
- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath {
    NSLog(@"START cellForRowAtIndexPath");

    NSArray *words = nil;
    if (tableView == self.searchDisplayController.searchResultsTableView) {
        words = _searchedWords;
    } else {
        words = _words;
    }

    UITableViewCell *cell = [[UITableViewCell alloc] init];
    Word *word = words[indexPath.row];
    cell.textLabel.text = word.spelling;
    cell.accessoryType = UITableViewCellAccessoryDisclosureIndicator;

    return cell;
}
- (void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath {
    NSArray *words = nil;
    if (tableView == self.searchDisplayController.searchResultsTableView) {
        words = _searchedWords;
    } else {
        words = _words;
    }

    WordsShowViewController *controller = [[WordsShowViewController alloc] initWithNibName:@"ViewController" bundle:nil];
    controller.word = (Word *)words[indexPath.row];
    [self.navigationController pushViewController:controller animated:YES];
}

#pragma mark - related to Search Bar
- (BOOL)searchDisplayController:(UISearchDisplayController *)controller shouldReloadTableForSearchString:(NSString *)searchString {
    NSLog(@"Query: %@", searchString); // NOT CALLED...

    [self filterContentForSearchText:searchString
        scope:[
            [self.searchDisplayController.searchBar scopeButtonTitles]
            objectAtIndex:[self.searchDisplayController.searchBar selectedScopeButtonIndex]
        ]
    ];

    return YES;
}
- (void)filterContentForSearchText:(NSString*)searchString scope:(NSString*)scope {
    NSLog(@"START filterContentForSearchText"); // NOT CALLED...

    [_searchedWords removeAllObjects];

    for(Word *word in _words) {
        NSRange range = [word.spelling rangeOfString:searchString options:NSCaseInsensitiveSearch];
        if(range.length > 0) {
            [_searchedWords addObject:word];
        }
    }
}

@end

Word.h

#import <Foundation/Foundation.h>

@interface Word : NSObject

@property (strong, nonatomic) NSString *identifier;
@property (strong, nonatomic) NSString *spelling;

- (id)initWith:(NSString *)spelling;

@end

Word.m

#import "Word.h"

@implementation Word

- (id)initWith:(NSString *)spelling {
    self = [super init];
    if (!self) {
        return nil;
    }

    CFUUIDRef uuid = CFUUIDCreate(NULL);
    _identifier = (NSString *)CFBridgingRelease(CFUUIDCreateString(NULL, uuid));
    CFRelease(uuid);

    _spelling = spelling;

    return self;
}

@end

С Уважением,