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Right Now I am making an iOS app and I would like to implement the ability to remove letters in a UILabel by simply "Dropping the letter". The part That I am having an issue with is adding a gesture recognizer to individual letters of a UILabel. I have already searched the web for this and have nothing.Just to be clear, I am NOT adding a gesture recognizer to the whole label, I am only wanting to add it to individual letters. Any help is greatly appreciated.

Thanks

virindh
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3 Answers3

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It seems that the easiest way to do it is by dynamically calculating the position of a letter. Use this:

CGSize textSize = [text sizeWithFont:[UIFont boldSystemFontOfSize:size]
                   constrainedToSize:constrainedSize
                       lineBreakMode:NSLineBreakByWordWrapping];

so you can get the the size for a letter in the font and size you are using for each label and using the [stringInstance length] property and the [UILabel numberOfLines] property to get the approximate center for each letter in a label, then use a simple tapGestureRecognizer for each label and in there calling your method for 

- (NSString*)letterForPoint:(CGPoint)tapCenter inLabel:(UILabel*)label;

there you use everything to calculate the approximate center for each letter and adding a selectableRange for error and correct user responding as x +- 20 pixels and y +- 20 pixels.

Apple says that anything with a selectable bound lesser than 40 pixels for 40 pixels will be completely annoying for the user, so your font size should actually be quite big for user interaction.

Pang
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Sergio Prado
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If I am understanding correctly, it sounds like subclassing UILabel would make sense.

Make a LetterLabel: UILabel class and in the init set up your GestureRecognizer on self.

Then when you create your letters each one will have the recognizer attached to it

LetterLabel *firstLetter = [[LetterLabel alloc] init]
LetterLabel *secondLetter = [[LetterLabel alloc] init]
Adam Johnson
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  • I cant do that because I need the text of the whole UILabel. It would be hard managing so many labels and I cant get the whole text. It would also drastically reduce performance. – virindh Nov 30 '12 at 23:51
  • You could add each letter into a word array. – Adam Johnson Nov 30 '12 at 23:55
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UIGestureRecognizer can only be applied to a UIView or subclass of that (e.g. a UILabel, like Adam suggested). If you are worried about performance, then I think your next step would be to:

1) Subclass UIView in order to create a custom implementation of a UILabel-like view.

2) Draw out the custom label's string to in the drawInRect: method

3) Use the touchesBegan:withEvent:, touchesMoved:withEvent:, and touchesEnded:withEvent: methods to track finger positions in order to move/redraw characters of the backing string.

EDIT:

Alternatively, you could use one UIPanGestureRecognizer on a the custom label to track finger positions, and move around sublayers within the bounds of the custom label (each sublayer could contain a character in the string). In this way, you could more easily take advantage of Core Animation to animate the characters (i.e. create the "dropping" effect).

RyanM
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  • Is there any sort of example for this... I am not entirely clear as to what you are suggesting. Sorry. – virindh Dec 01 '12 at 00:14
  • @user1418074 Drawing a string in a UIView or subclass: http://stackoverflow.com/a/12358605/272302 (drawing a string in a CALayer is very similar... CALayer's draw method gives you a CGContextRef: http://stackoverflow.com/questions/2209734/add-text-to-calayer). That should help with the drawing code. – RyanM Dec 01 '12 at 00:28
  • @user1418074 This should help with creating CALayers and adding them to a parent layer (the parent layer in this example would be the layer associated with the custom label you'd create): http://www.raywenderlich.com/2502/introduction-to-calayers-tutorial – RyanM Dec 01 '12 at 00:31