Add tap event to IOS NSMutableAttributedString

Question

I have an NSMutableAttributedString such as \"Bob liked your picture\".

I\'m wondering if I can add two different tap events to \"Bob\" and \"picture\". Ideally, tap

Answer 1

You can achieve this by using CoreText to implement a method that will retrieve the index of the character the user selected / touched. First, using CoreText, draw your attributed string in a custom UIView sub class. An example overridden drawRect: method:

- (void) drawRect:(CGRect)rect
{
    // Flip the coordinate system as CoreText's origin starts in the lower left corner
    CGContextRef context = UIGraphicsGetCurrentContext();

    CGContextTranslateCTM(context, 0.0f, self.bounds.size.height);
    CGContextScaleCTM(context, 1.0f, -1.0f);

    UIBezierPath *path = [UIBezierPath bezierPathWithRect:self.bounds];
    CTFramesetterRef frameSetter = CTFramesetterCreateWithAttributedString((__bridge   CFAttributedStringRef)(_attributedString));

    if(textFrame != nil) {
        CFRelease(textFrame);
    }

    // Keep the text frame around.
    textFrame = CTFramesetterCreateFrame(frameSetter, CFRangeMake(0, 0), path.CGPath, NULL);
    CFRetain(textFrame);

    CTFrameDraw(textFrame, context);
}

Secondly, create a method that interrogates the text to find the character index for a given point:

- (int) indexAtPoint:(CGPoint)point
{
    // Flip the point because the coordinate system is flipped.
    point = CGPointMake(point.x, CGRectGetMaxY(self.bounds) - point.y);
    NSArray *lines = (__bridge NSArray *) (CTFrameGetLines(textFrame));

    CGPoint origins[lines.count];
    CTFrameGetLineOrigins(textFrame, CFRangeMake(0, lines.count), origins);

    for(int i = 0; i < lines.count; i++) {
        if(point.y > origins[i].y) {
            CTLineRef line = (__bridge CTLineRef)([lines objectAtIndex:i]);
            return CTLineGetStringIndexForPosition(line, point);
        }
    }

    return 0;
}

Lastly, you can override the touchesBegan:withEvent: method to get the location of where the user touched and convert that into a character index or range:

- (void) touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event
{
    UITouch *t = [touches anyObject];
    CGPoint tp = [t locationInView:self];
    int index = [self indexAtPoint:tp];

    NSLog(@"Character touched : %d", index);
}

Be sure to include CoreText into your project and clean up any resources (like text frames) you keep around as that memory is not managed by ARC.