如何延迟搜索结果显示在表格视图中？

Question

I'm a new on programming, especially obj-c. I'm developing a search bar in an iOS app that dig into a quite big database (8.000+ entries and growing), but as soon as I type in the search field, it starts to give back results filtering while typing because of the large amount of data, it almost freeze the keyboard. My guess was to let the search start after 4 digits, so instead of looking out from 8.000+ entries it would have do it out of a smaller subset, but with the code I wrote it keeps on freezing, after 4 digits...

Any hints?

Thank you,

Here is my code:

- (void)searchBar:(UISearchBar *)searchBar textDidChange:(NSString *)searchText
{
    NSUInteger length = [searchText length];
    if (![NSString isEmpty:searchText] & (length > 3))
    {
        self.filteredItems = [self.sedi filterMatch:^BOOL(id elem)
                          {
                              Sede *sede = (Sede *)elem;
                                  NSArray *split = [searchText componentsSeparatedByString:@" "];

                                  return [sede.nome matchAll:split] ||
                                  [sede.descrizione matchAll:split] ||
                                  [sede.indirizzo matchAll:split] ||
                                  [sede.generi matchAll:split];
                              }
                                           contains:^BOOL(id elem)
                              {
                                  Sede *sede = (Sede *)elem;
                                  NSArray *split = [searchText componentsSeparatedByString:@" "];
                                  return [sede.nome containsAll:split] ||
                                  [sede.descrizione containsAll:split] ||
                                  [sede.indirizzo containsAll:split] ||
                                  [sede.generi containsAll:split];
                              }];
        [self.searchDisplayController.searchResultsTableView reloadData];
    }
}

Answer 1

First off, as rmaddy said, you may be better off just having the user hit the "Search" button for simplicity's sake.

That said, you should be able to accomplish this with an NSOperationQueue .

First, create an ivar or property:

NSOperationQueue *_searchOperationQueue;

Then, initialize it somewhere, probably viewDidLoad

_searchOperationQueue = [NSOperationQueue new];
_searchOperationQueue.maxConcurrentOperationCount = 1;

Then, you should be able to wrap your code in an NSOperation like this:

- (void)searchBar:(UISearchBar *)searchBar textDidChange:(NSString *)searchText
{
    // cancel any existing search
    [_searchOperationQueue cancelAllOperations];

    // begin new search
    [_searchOperationQueue addOperationWithBlock:^{
        NSUInteger length = [searchText length];
        if (![NSString isEmpty:searchText] && (length > 3))
        {

          NSArray *filteredTemp = [self.sedi filterMatch:^BOOL(id elem)
                                  {
                                  Sede *sede = (Sede *)elem;
                                      NSArray *split = [searchText componentsSeparatedByString:@" "];

                                      return [sede.nome matchAll:split] ||
                                      [sede.descrizione matchAll:split] ||
                                      [sede.indirizzo matchAll:split] ||
                                      [sede.generi matchAll:split];
                                  }
                                               contains:^BOOL(id elem)
                                  {
                                      Sede *sede = (Sede *)elem;
                                      NSArray *split = [searchText componentsSeparatedByString:@" "];
                                      return [sede.nome containsAll:split] ||
                                      [sede.descrizione containsAll:split] ||
                                      [sede.indirizzo containsAll:split] ||
                                      [sede.generi containsAll:split];
                                  }];
              // update view on main thread
              dispatch_async(dispatch_get_main_queue(), ^{
                self.filteredItems = filteredTemp;
                [self.searchDisplayController.searchResultsTableView reloadData];
              });
        }
    }];
}

I have used code almost identical to this for filtering large lists with very good results. You just have to be careful to keep the model and view in sync by only accessing it on the main thread (which is what I did at the end).

One last thing to note is that you were using a bitwise "AND" ( & ) rather than a conditional "AND" ( && ) in your code, which I corrected in my answer. While it may actually function correctly in this particular case, it was almost certainly a mistake, so be careful.