Question

I’m implementing a search field that filters a UITableView according to the text the user enters.
The TableView is built from an array that holds NSStrings (the data to display and search) and may contain 6000+ items.
When the user starts the search, I’m implementing the -(void)searchBar:(UISearchBar *)searchBar textDidChange:(NSString *)searchText method.

My code works, however, when the data array is large, it is very slow and creating a really bad user experience (my iPhone 4s get stuck for a good few seconds).

The way I’m implementing the search (in the method mentioned above) is this:

NSMutableArray *discardedItems = [[NSMutableArray alloc] init]; // Items to be removed
searchResultsArray = [[NSMutableArray alloc] initWithArray:containerArray]; // The array that holds all the data

// Search for matching results
for (int i=0; i<[searchResultsArray count]; i++) {   
    NSString *data = [[containerArray objectAtIndex:i] lowercaseString];
    NSRange r = [data rangeOfString:searchText];
    if (r.location == NSNotFound) {
        // Mark the items to be removed
        [discardedItems addObject:[searchResultsArray objectAtIndex:i]];
    }
}
// update the display array
[searchResultsArray removeObjectsInArray:discardedItems];
[myTableView reloadData];

I did not think that looping over an array with a few thousand items would cause any issue…
Any suggestion will be appreciated!

UPDATE
I’ve just realized that what takes most of the time is this:

[searchResultsArray removeObjectsInArray:discardedItems];

Answer 1

Try fast enumeration way, my snippet:

- (void)searchBar:(UISearchBar*)searchBar textDidChange:(NSString*)text
{
    if(text.length == 0)
    {
        self.isFiltered = NO;
    }
    else
    {
        self.isFiltered = YES;
        self.searchArray = [NSMutableArray arrayWithCapacity:self.places.count];

        for (PTGPlace* place in self.places)
        {
            NSRange nameRange = [place.name rangeOfString:text options:NSCaseInsensitiveSearch];

            if(nameRange.location != NSNotFound)
            {
                [self.searchArray addObject:place];
            }
        }
    }

    [self.tableView reloadData];
}

- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section
{
    if(self.isFiltered)
        return self.searchArray.count;
    else
        return self.places.count;
}

In cellForRowAtIndexPath:

    PTGPlace *place = nil;

    if(self.isFiltered)
        place = [self.searchArray objectAtIndex:indexPath.row];
    else
        place = [self.places objectAtIndex:indexPath.row];

    // Configure the cell...
    cell.textLabel.text = place.name;
    cell.detailTextLabel.text = [place subtitle];