UILabel negative line spacing

Building off of Eric Murphey's answer, I've created an extension in Swift 4 syntax.

extension UILabel{    
    public func zeroLineSpace(){
        let s = NSMutableAttributedString(string: self.text!)
        let style = NSMutableParagraphStyle()
        let lineHeight = self.font.pointSize - self.font.ascender + self.font.capHeight
        let offset = self.font.capHeight - self.font.ascender
        let range = NSMakeRange(0, self.text!.count)
        style.maximumLineHeight = lineHeight
        style.minimumLineHeight = lineHeight
        style.alignment = self.textAlignment
        s.addAttribute(.paragraphStyle, value: style, range: range)
        s.addAttribute(.baselineOffset, value: offset, range: range)
        self.attributedText = s
    }
}

Simply call it like so

myUiLabel.zeroLineSpace()

NSMutableAttributedString* attrString = [[NSMutableAttributedString alloc] initWithString:labelText];
NSMutableParagraphStyle *style = [[NSMutableParagraphStyle alloc] init];
CGFloat minMaxLineHeight = (font.pointSize - font.ascender + font.capHeight);
NSNumber *offset = @(font.capHeight - font.ascender);
NSRange range = NSMakeRange(0, labelText.length);
[style setMinimumLineHeight:minMaxLineHeight];
[style setMaximumLineHeight:minMaxLineHeight];
if (isCentered) {
    [style setAlignment:NSTextAlignmentCenter];
}
[attrString addAttribute:NSParagraphStyleAttributeName
                   value:style
                   range:range];
[attrString addAttribute:NSBaselineOffsetAttributeName
                   value:offset
                   range:range];

This should get you near zero spacing on the text and should be safe to use with any font type and size.

Please see the following documentation from Apple setLineSpacing - NSMutableParagraphStyle , value must not be negative

setLineSpacing: Sets the distance in points added between lines within the paragraph to aFloat.

 - (void)setLineSpacing:(CGFloat)aFloat

Discussion

This value must be nonnegative.

There are also methods related to the minimum and maximum height for lines… probably setting line space to 0 and modifying the height could help you to achieve the effect you want-