KVO观察者模式不可以这么用吗

Question

• (void)viewDidLoad
  {
  [super viewDidLoad];
  [self dataArray];
  [self createNav];
  [self createTableView];
  [self createsearchBar];

  [_searchBar addObserver:self forKeyPath:@"text" options:NSKeyValueObservingOptionNew context:nil];

}

• (void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary *)change context:(void *)context{ NSLog(@"%@%@%@",keyPath,change,context); if (_searchBar.text.length==0) { NSLog(@"!!!!!!"); _searchBar=nil; [_tableView reloadData]; } NSLog(@"----");

}