Get index of character in UILabel from tap
I would like to get the index for the involved symbol on the UILabel. I subclassed UILabel. In my awakeFromNib () I have this:
layoutManager = NSLayoutManager()
textStorage = NSTextStorage(attributedString: self.attributedText)
textStorage.addLayoutManager(layoutManager)
textContainer = NSTextContainer(size: CGSizeMake(self.frame.size.width, self.frame.size.height))
textContainer.lineFragmentPadding = 0
textContainer.maximumNumberOfLines = self.numberOfLines
textContainer.lineBreakMode = self.lineBreakMode
textContainer.size = self.frame.size
layoutManager.addTextContainer(textContainer)
It works the way I want it to be for the first 5 characters of the label, since I touched the first character and in my contacts. I got index 0:
var touchedCharacterIndex = layoutManager.characterIndexForPoint(touch.locationInView(self), inTextContainer: textContainer, fractionOfDistanceBetweenInsertionPoints: nil)
But when I click somewhere past the first four characters of the UILabel, I get either 4 or 0, which is not correct.
Thank,
Update
From a suggestion in the comments, I added the following:
func updateTextStorage() {
if let attributedText = self.attributedText {
textStorage = NSTextStorage(attributedString: attributedText)
}
textStorage?.addLayoutManager(layoutManager)
textContainer = NSTextContainer(size: CGSizeMake(self.frame.size.width, self.frame.size.height))
textContainer?.lineFragmentPadding = 7
textContainer?.maximumNumberOfLines = self.numberOfLines
textContainer?.lineBreakMode = self.lineBreakMode
textContainer?.size = self.bounds.size
layoutManager.addTextContainer(textContainer!)
layoutManager.textStorage = textStorage
}
I call it in layoutSubviews()
, awakFromNib
and setters bounds
, frame
, attributedText
and text
.
And now it gives me some weird indices, like if the text length is 21, pressing the first letter gives me 6.
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TL; DR: You get some weird indexes because the line yours layoutManager
see is exposed differently than the one you actually see on screen.
You get some weird indexes:
- (NSUInteger)characterIndexForPoint:(CGPoint)point
inTextContainer:(NSTextContainer *)container
fractionOfDistanceBetweenInsertionPoints:(nullable CGFloat *)partialFraction;
because your own layoutManager
needs to be in sync with the internal one layoutManager
from the system UILabel
. This means that when you set the font, size, etc. On its own label, the inner layoutManager
knows about it because it took care of it UILabel
, but your instance layoutManager
doesn't.
So the layout of the text as seen by your layoutManager is in a different position than the actual text displayed by the label on the screen (default font size and size).
The tricky part is to keep these properties in sync, what you can do is set those from your attributed text like:
[mutableAttributedString addAttribute:NSFontAttributeName
value:self.font
range:NSMakeRange(0, mutableAttributedString.string.length)];
And pass this attribute string to your instance NSTextStorage
. This fixed all problems for me.
INFO: to help you debug, you can display the line "seen" by yours layoutManager
using the following command:
- (void)drawTextInRect:(CGRect)rect
{
[super drawTextInRect:rect];
[self.layoutManager drawGlyphsForGlyphRange:NSMakeRange(0, self.textStorage.length) atPoint:CGPointMake(0, 0)];
}
If you see two lines stacked on top of each other with some glitches, that's your problem right there. If you can only see the one that should be, because they are perfectly aligned and you are good!
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I think the problem is with the NSTextContainer outputting the text as a UITextView, which means it will not be vertically centered like a UILabel.
If you run the following piece of code, you can see where the glyphs are laid out.
var location = layoutManager.locationForGlyphAtIndex(0);
It should show that the glyphs are laid out at the top of your text container.
So when you call
var point = tapGesture.locationInView(self);
needs to be adjusted to accommodate the vertical displacement of the UILabel.
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I am trying to find something that works for this. Here's what I was able to get started. This draws from several other examples, but I had to include the paragraph style to make it match exactly. Hope this helps someone else.
NSLayoutManager *layoutManager = [[NSLayoutManager alloc] init];
NSTextContainer *textContainer = [[NSTextContainer alloc] initWithSize:CGSizeZero];
NSTextStorage *textStorage;
NSMutableParagraphStyle *paragraphStyle = NSMutableParagraphStyle.new;
paragraphStyle.alignment = self.label.textAlignment;
// Configure textContainer
textContainer.lineFragmentPadding = 0.0;
textContainer.lineBreakMode = self.label.lineBreakMode;
textContainer.maximumNumberOfLines = self.label.numberOfLines;
CGPoint locationOfTouchInLabel = [tapGesture locationInView:tapGesture.view];
CGSize labelSize = tapGesture.view.bounds.size;
textContainer.size = self.label.bounds.size;
NSMutableAttributedString *attributedText = [[NSMutableAttributedString alloc] initWithAttributedString:self.noPoliciesDescriptionLabel.attributedText];
[attributedText addAttributes:@{NSFontAttributeName: self.label.font, NSParagraphStyleAttributeName: paragraphStyle} range:NSMakeRange(0,self.label.attributedText.string.length)];
textStorage = [[NSTextStorage alloc] initWithAttributedString:attributedText];
// Configure layoutManager and textStorage
[layoutManager addTextContainer:textContainer];
[textStorage addLayoutManager:layoutManager];
CGRect textBoundingBox = [layoutManager usedRectForTextContainer:textContainer];
CGPoint textContainerOffset = CGPointMake((labelSize.width - textBoundingBox.size.width) * 0.5 - textBoundingBox.origin.x,
(labelSize.height - textBoundingBox.size.height) * 0.5 - textBoundingBox.origin.y);
CGPoint locationOfTouchInTextContainer = CGPointMake(locationOfTouchInLabel.x - textContainerOffset.x,
locationOfTouchInLabel.y - textContainerOffset.y);
NSInteger indexOfCharacter = [layoutManager characterIndexForPoint:locationOfTouchInTextContainer
inTextContainer:textContainer
fractionOfDistanceBetweenInsertionPoints:nil];
NSRange range = NSMakeRange(indexOfCharacter, 1);
NSString *value = [self.label.text substringWithRange:range];
NSLog(@"%@, %zd, %zd" , value, range.location, range.length);
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