Character index at touch point for UILabel

Question

For a UILabel, I\'d like to find out which character index is at specific point received from a touch event. I\'d like to solve this problem for iOS 7 using Tex

Answer 1

Here you are my implementation for the same problem. I have needed to mark #hashtags and @usernames with reaction on the taps.

I do not override drawTextInRect:(CGRect)rect because default method works perfect.

Also I have found the following nice implementation https://github.com/Krelborn/KILabel. I used some ideas from this sample too.

@protocol EmbeddedLabelDelegate 
- (void)embeddedLabelDidGetTap:(EmbeddedLabel *)embeddedLabel;
- (void)embeddedLabel:(EmbeddedLabel *)embeddedLabel didGetTapOnHashText:(NSString *)hashStr;
- (void)embeddedLabel:(EmbeddedLabel *)embeddedLabel didGetTapOnUserText:(NSString *)userNameStr;
@end

@interface EmbeddedLabel : UILabel
@property (nonatomic, weak) id delegate;
- (void)setText:(NSString *)text;
@end


#define kEmbeddedLabelHashtagStyle      @"hashtagStyle"
#define kEmbeddedLabelUsernameStyle     @"usernameStyle"

typedef enum {
    kEmbeddedLabelStateNormal = 0,
    kEmbeddedLabelStateHashtag,
    kEmbeddedLabelStateUsename
} EmbeddedLabelState;


@interface EmbeddedLabel ()

@property (nonatomic, strong) NSLayoutManager *layoutManager;
@property (nonatomic, strong) NSTextStorage   *textStorage;
@property (nonatomic, weak)   NSTextContainer *textContainer;

@end


@implementation EmbeddedLabel

- (void)dealloc
{
    _delegate = nil;
}

- (id)initWithFrame:(CGRect)frame
{
    self = [super initWithFrame:frame];

    if (self)
    {
        [self setupTextSystem];
    }
    return self;
}

- (void)awakeFromNib
{
    [super awakeFromNib];
    [self setupTextSystem];
}

- (void)setupTextSystem
{
    self.userInteractionEnabled = YES;
    self.numberOfLines = 0;
    self.lineBreakMode = NSLineBreakByWordWrapping;

    self.layoutManager = [NSLayoutManager new];

    NSTextContainer *textContainer     = [[NSTextContainer alloc] initWithSize:self.bounds.size];
    textContainer.lineFragmentPadding  = 0;
    textContainer.maximumNumberOfLines = self.numberOfLines;
    textContainer.lineBreakMode        = self.lineBreakMode;
    textContainer.layoutManager        = self.layoutManager;

    [self.layoutManager addTextContainer:textContainer];

    self.textStorage = [NSTextStorage new];
    [self.textStorage addLayoutManager:self.layoutManager];
}

- (void)setFrame:(CGRect)frame
{
    [super setFrame:frame];
    self.textContainer.size = self.bounds.size;
}

- (void)setBounds:(CGRect)bounds
{
    [super setBounds:bounds];
    self.textContainer.size = self.bounds.size;
}

- (void)layoutSubviews
{
    [super layoutSubviews];
    self.textContainer.size = self.bounds.size;
}

- (void)setText:(NSString *)text
{
    [super setText:nil];

    self.attributedText = [self attributedTextWithText:text];
    self.textStorage.attributedString = self.attributedText;

    [self.gestureRecognizers enumerateObjectsUsingBlock:^(UIGestureRecognizer *recognizer, NSUInteger idx, BOOL *stop) {
        if ([recognizer isKindOfClass:[UITapGestureRecognizer class]]) [self removeGestureRecognizer:recognizer];
    }];
    [self addGestureRecognizer:[[UITapGestureRecognizer alloc] initWithTarget:self action:@selector(embeddedTextClicked:)]];
}

- (NSMutableAttributedString *)attributedTextWithText:(NSString *)text
{
    NSMutableParagraphStyle *style = [NSMutableParagraphStyle new];
    style.alignment = self.textAlignment;
    style.lineBreakMode = self.lineBreakMode;

    NSDictionary *hashStyle   = @{ NSFontAttributeName : [UIFont boldSystemFontOfSize:[self.font pointSize]],
                                   NSForegroundColorAttributeName : (self.highlightedTextColor ?: (self.textColor ?: [UIColor darkTextColor])),
                                   NSParagraphStyleAttributeName : style,
                                   kEmbeddedLabelHashtagStyle : @(YES) };

    NSDictionary *nameStyle   = @{ NSFontAttributeName : [UIFont boldSystemFontOfSize:[self.font pointSize]],
                                   NSForegroundColorAttributeName : (self.highlightedTextColor ?: (self.textColor ?: [UIColor darkTextColor])),
                                   NSParagraphStyleAttributeName : style,
                                   kEmbeddedLabelUsernameStyle : @(YES)  };

    NSDictionary *normalStyle = @{ NSFontAttributeName : self.font,
                                   NSForegroundColorAttributeName : (self.textColor ?: [UIColor darkTextColor]),
                                   NSParagraphStyleAttributeName : style };

    NSMutableAttributedString *attributedText = [[NSMutableAttributedString alloc] initWithString:@"" attributes:normalStyle];
    NSCharacterSet *charSet = [NSCharacterSet characterSetWithCharactersInString:kWhiteSpaceCharacterSet];
    NSMutableString *token = [NSMutableString string];
    NSInteger length = text.length;
    EmbeddedLabelState state = kEmbeddedLabelStateNormal;

    for (NSInteger index = 0; index < length; index++)
    {
        unichar sign = [text characterAtIndex:index];

        if ([charSet characterIsMember:sign] && state)
        {
            [attributedText appendAttributedString:[[NSAttributedString alloc] initWithString:token attributes:state == kEmbeddedLabelStateHashtag ? hashStyle : nameStyle]];
            state = kEmbeddedLabelStateNormal;
            [token setString:[NSString stringWithCharacters:&sign length:1]];
        }
        else if (sign == '#' || sign == '@')
        {
            [attributedText appendAttributedString:[[NSAttributedString alloc] initWithString:token attributes:normalStyle]];
            state = sign == '#' ? kEmbeddedLabelStateHashtag : kEmbeddedLabelStateUsename;
            [token setString:[NSString stringWithCharacters:&sign length:1]];
        }
        else
        {
            [token appendString:[NSString stringWithCharacters:&sign length:1]];
        }
    }

    [attributedText appendAttributedString:[[NSAttributedString alloc] initWithString:token attributes:state ? (state == kEmbeddedLabelStateHashtag ? hashStyle : nameStyle) : normalStyle]];
    return attributedText;
}

- (void)embeddedTextClicked:(UIGestureRecognizer *)recognizer
{
    if (recognizer.state == UIGestureRecognizerStateEnded)
    {
        CGPoint location = [recognizer locationInView:self];

        NSUInteger characterIndex = [self.layoutManager characterIndexForPoint:location
                                                           inTextContainer:self.textContainer
                                  fractionOfDistanceBetweenInsertionPoints:NULL];

        if (characterIndex < self.textStorage.length)
        {
            NSRange range;
            NSDictionary *attributes = [self.textStorage attributesAtIndex:characterIndex effectiveRange:&range];

            if ([attributes objectForKey:kEmbeddedLabelHashtagStyle])
            {
                NSString *value = [self.attributedText.string substringWithRange:range];
                [self.delegate embeddedLabel:self didGetTapOnHashText:[value stringByReplacingOccurrencesOfString:@"#" withString:@""]];
            }
            else if ([attributes objectForKey:kEmbeddedLabelUsernameStyle])
            {
                NSString *value = [self.attributedText.string substringWithRange:range];
                [self.delegate embeddedLabel:self didGetTapOnUserText:[value stringByReplacingOccurrencesOfString:@"@" withString:@""]];
            }
            else
            {
                [self.delegate embeddedLabelDidGetTap:self];
            }
        }
        else
        {
            [self.delegate embeddedLabelDidGetTap:self];
        }
    }
}

@end