Suggest # tags while typing (like Twitter) for iPhone UITextView

Question

I'd building an app that uses hashtags, like Twitter or Tweetbot. When you're typing a message, if you type the hashtag symbol, I'd like to suggest tags that match the current one you're typing.

I've already figured out how to get the UITableView to appear and show a list of hashtags, but what I can't figure out is how to do the following:

1. Get the NSRange of the current word being typed,
2. See if that range is formatted like a hashtag (NSRegularExpression @"#\\w\\w*")
3. (From here on out, I've got the code figured out to search for matching hashtags and show them in the UITableView)

Can anyone help me with steps 1 and 2? I've been thinking about using textViewDidChange:, but I'm concerned that the app's performance might suffer if I'm constantly running methods every time the characters change.

Thanks!

Answer 1

I figured it out! I wound up using the textViewDidChange: and textViewDidChangeSelection: methods.

To get the NSRange of the current hashtag being typed, I ran a for loop over the NSRegularExpression matches in the text string. From there, I used NSLocationInRange to find out if the current cursor position intersected any of the hashtags.

Here's the code:

//Get the ranges of current hashtags
NSArray *hashtagRanges = [StringChecker rangesOfHashtagsInString:textView.text];
NSTextCheckingResult *currentHashtag;

if ([hashtagRanges count] >0)
{
    //List the ranges of all the hashtags
    for (int i = 0; i<[hashtagRanges count]; i++) 
    {
        NSTextCheckingResult *hashtag = [hashtagRanges objectAtIndex:i];
        //Check if the currentRange intersects the hashtag
        //Have to add an extra space to the range for if you're at the end of a hashtag. (since NSLocationInRange uses a < instead of <=)
        NSRange currentlyTypingHashtagRange = NSMakeRange(hashtag.range.location, hashtag.range.length + 1);
        if (NSLocationInRange(currentRange.location, currentlyTypingHashtagRange))
        {
            //If the cursor is over the hashtag, then snag that hashtag for matching purposes.
            currentHashtag = hashtag;
        }
    }

    if (currentHashtag){
        //If we found one hashtag that we're currently editing

        //Display the hashtag suggester, feed it the current hashtag for matching.
        [self showTagTable];

        //Get the current list of hashtags into an array
        NSFetchRequest *hashtagRequest = [[NSFetchRequest alloc] init];
        NSEntityDescription *tagEntityDescription = [NSEntityDescription entityForName:@"Tags" 
                                                                inManagedObjectContext:self.note.managedObjectContext];
        [hashtagRequest setEntity:tagEntityDescription];
        NSSortDescriptor *sortDescriptor = [NSSortDescriptor sortDescriptorWithKey:@"dateLastUsed" 
                                                                         ascending:YES];
        NSArray *sortDescriptors = [NSArray arrayWithObject:sortDescriptor];
        [hashtagRequest setSortDescriptors:sortDescriptors];

        NSPredicate *tagPredicate = [NSPredicate predicateWithFormat:@"name contains[c] %@", [noteTextView.text substringWithRange:currentHashtag.range]];
        [hashtagRequest setPredicate:tagPredicate];

        tagsToDisplay = (NSMutableArray *)[self.note.managedObjectContext executeFetchRequest:hashtagRequest error:nil];
        [tagListTable reloadData];

        //If there are no matching hashtags, then let's hide the tag table.
        if ([tagsToDisplay count] == 0) 
        {
            [self hideTagTable];
            return;
        }

    }

The StringChecker class is a custom one that I wrote, it just has class methods that parse the strings. I made StringChecker a class because the methods are used in several places in the app. Here's the method:

    #pragma mark - Hashtag Methods
+(NSArray *)rangesOfHashtagsInString:(NSString *)string {
    NSRegularExpression *hashtagDetector = [[NSRegularExpression alloc] initWithPattern:@"#\\w\\w*" 
                                                                                options:NSRegularExpressionCaseInsensitive 
                                                                                  error:nil];    
    NSArray *hashtagRanges = [hashtagDetector matchesInString:string
                                                      options:NSMatchingWithoutAnchoringBounds
                                                        range:NSMakeRange(0, string.length)];
    return hashtagRanges;
}

+(NSUInteger)numberOfHashtagsInString:(NSString *)string {
    NSRegularExpression *hashtagDetector = [[NSRegularExpression alloc] initWithPattern:@"#\\w\\w*" 
                                                                                options:NSRegularExpressionCaseInsensitive 
                                                                                  error:nil];
    NSUInteger numberOfHashtags = [hashtagDetector numberOfMatchesInString:string
                                                                   options:NSRegularExpressionCaseInsensitive
                                                                     range:NSMakeRange(0, string.length)];
    return numberOfHashtags;
}

Answer 2

Another way I figured out to do this is as follows.

In the - (BOOL)textView:(UITextView *)textView shouldChangeTextInRange:(NSRange)range replacementText:(NSString *)text function I put a listener for a # being typed which begins recording the characters following the hash until the user types a space at which time it resets.

if ([text isEqualToString:@"#"]) {
    recordingHashTag = YES;
    startParse = range.location;

}else if ([text isEqualToString:@" "]) {
    currentHashTag = nil;
    recordingHashTag = NO;
    theTable.hidden = YES;

}

if (recordingHashTag == YES) {
    NSString *value;
    if (startParse > [textView.text length] - startParse) {
        value = [textView.text substringWithRange:NSMakeRange(startParse, [textView.text length] - startParse)];
        [self filterHashTagTableWithHash:value];
    }
}

If the BOOL recordingHashTag is set to YES I pass the substring containing the hashtag text to a function which searches a pre populated array of hashtags. If there is a match it adds that entry to a filtered array of hashtags which it uses to populate the tableview on the fly.

-(void)filterHashTagTableWithHash:(NSString *)hash{

    [self.filterHashTagArray removeAllObjects];

    for (NSString *hashTag in self.hashTagArray ){
        NSRange result = [hashTag rangeOfString:hash options:NSCaseInsensitiveSearch];
        if (result.location != NSNotFound) {
            [filterHashTagArray addObject:hashTag];
        }
    }
    if (filterHashTagArray.count) {
        theTable.hidden = NO;
    }else{
        theTable.hidden = YES;
    }

    [self.theTable reloadData];
}

The final step is to insert the hash tag when the user clicks on the entry in the table.

    - (void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath{
    UITableViewCell *cell = (UITableViewCell*)[self tableView:theTable cellForRowAtIndexPath:indexPath];

    NSString *newString = [textViewComment.text stringByReplacingCharactersInRange:NSMakeRange(startParse, [textViewComment.text length] - startParse) withString:cell.textLabel.text];
    textViewComment.text = newString;
}

Just don't forget to clear out your variables when a user backspaces mid hash tag.