swift - Adding padding to a UILabel with a background colour

Question

I have a multiline UILabel that contains an NSAttributedString, and this has a background colour applied to give the above effect.

This much is fine but I need padding within the label to give a bit of space on the left. There are other posts on SO addressing this issue, such as by subclassing UILabel to add UIEdgeInsets. However, this merely added padding to the outside of the label for me.

Any suggestions on how padding can be added to this label?

EDIT: Apologies if this has been confusing, but the end goal is something like this...

Answer 1

Based on the answer provided here: https://stackoverflow.com/a/59216224/6257435

Just to demonstrate (several hard-coded values which would, ideally, be dynamic / calculated):

class ViewController: UIViewController, NSLayoutManagerDelegate {
    
    var myTextView: UITextView!
    let textStorage = MyTextStorage()
    let layoutManager = MyLayoutManager()
    
    override func viewDidLoad() {
        super.viewDidLoad()
        
        myTextView = UITextView()
        myTextView.translatesAutoresizingMaskIntoConstraints = false
        view.addSubview(myTextView)
        
        let g = view.safeAreaLayoutGuide
        
        NSLayoutConstraint.activate([
            myTextView.topAnchor.constraint(equalTo: g.topAnchor, constant: 40.0),
            myTextView.leadingAnchor.constraint(equalTo: g.leadingAnchor, constant: 40.0),
            myTextView.widthAnchor.constraint(equalToConstant: 248.0),
            myTextView.heightAnchor.constraint(equalToConstant: 300.0),
        ])
    
        self.layoutManager.delegate = self
        
        self.textStorage.addLayoutManager(self.layoutManager)
        self.layoutManager.addTextContainer(myTextView.textContainer)
        
        let quote = "This is just some sample text to demonstrate the word wrapping with padding at the beginning (leading) and ending (trailing) of the lines of text."
        self.textStorage.replaceCharacters(in: NSRange(location: 0, length: 0), with: quote)
        
        guard let font = UIFont(name: "TimesNewRomanPSMT", size: 24.0) else {
            fatalError("Could not instantiate font!")
        }
        let attributes: [NSAttributedString.Key : Any] = [NSAttributedString.Key.font: font]
        self.textStorage.setAttributes(attributes, range: NSRange(location: 0, length: quote.count))

        myTextView.isUserInteractionEnabled = false
        
        // so we can see the frame of the textView
        myTextView.backgroundColor = .systemTeal
    }
    
    func layoutManager(_ layoutManager: NSLayoutManager,
                       lineSpacingAfterGlyphAt glyphIndex: Int,
                       withProposedLineFragmentRect rect: CGRect) -> CGFloat { return 14.0 }
    
    func layoutManager(_ layoutManager: NSLayoutManager,
                       paragraphSpacingAfterGlyphAt glyphIndex: Int,
                       withProposedLineFragmentRect rect: CGRect) -> CGFloat { return 14.0 }
}

class MyTextStorage: NSTextStorage {
    
    var backingStorage: NSMutableAttributedString
    
    override init() {
        
        backingStorage = NSMutableAttributedString()
        super.init()
    }
    
    required init?(coder: NSCoder) {
        
        backingStorage = NSMutableAttributedString()
        super.init(coder: coder)
    }
    
    //    Overriden GETTERS
    override var string: String {
        get { return self.backingStorage.string }
    }
    
    override func attributes(at location: Int,
                             effectiveRange range: NSRangePointer?) -> [NSAttributedString.Key : Any] {
        
        return backingStorage.attributes(at: location, effectiveRange: range)
    }
    
    //    Overriden SETTERS
    override func replaceCharacters(in range: NSRange, with str: String) {
        
        backingStorage.replaceCharacters(in: range, with: str)
        self.edited(.editedCharacters,
                    range: range,
                    changeInLength: str.count - range.length)
    }
    
    override func setAttributes(_ attrs: [NSAttributedString.Key : Any]?, range: NSRange) {
        
        backingStorage.setAttributes(attrs, range: range)
        self.edited(.editedAttributes,
                    range: range,
                    changeInLength: 0)
    }
}

import CoreGraphics //Important to draw the rectangles

class MyLayoutManager: NSLayoutManager {
    
    override init() { super.init() }
    
    required init?(coder: NSCoder) { super.init(coder: coder) }
    
    override func drawBackground(forGlyphRange glyphsToShow: NSRange, at origin: CGPoint) {
        super.drawBackground(forGlyphRange: glyphsToShow, at: origin)
        
        self.enumerateLineFragments(forGlyphRange: glyphsToShow) { (rect, usedRect, textContainer, glyphRange, stop) in
            
            var lineRect = usedRect
            lineRect.size.height = 41.0
            
            let currentContext = UIGraphicsGetCurrentContext()
            currentContext?.saveGState()
            
            // outline rectangles
            //currentContext?.setStrokeColor(UIColor.red.cgColor)
            //currentContext?.setLineWidth(1.0)
            //currentContext?.stroke(lineRect)

            // filled rectangles
            currentContext?.setFillColor(UIColor.orange.cgColor)
            currentContext?.fill(lineRect)

            currentContext?.restoreGState()
        }
    }
}

Output (teal-background shows the frame):