I want to make several changes to UILabel text style by using NSAttributedString:

1. Part of the string must have a solid backgroundColor;
2. Some parts of the string must have a different font;
3. Some parts of the string must have a different foregroundColor;

But when i made these changes, i ran into the problem that backgroundColor has some spacing (vertical lines in the image) between (i think) other attributes (font/foregroundColor).

(See the full size image)

How can i fixed that?

Swift Playground code:

import PlaygroundSupport
import UIKit

let label = UILabel()
label.backgroundColor = .black
let text = "Hello   World!"
let nsText = NSString(string: text)

let attributedString = NSMutableAttributedString(string: text)

attributedString.addAttribute(.backgroundColor, value: UIColor.systemCyan, range: nsText.range(of: "Hello   Wo"))

attributedString.addAttribute(.font, value: UIFont.systemFont(ofSize: 100.0), range: nsText.range(of: "Hello"))

attributedString.addAttribute(.foregroundColor, value: UIColor.systemPurple, range: nsText.range(of: "   "))
attributedString.addAttribute(.font, value: UIFont.systemFont(ofSize: 80.0), range: nsText.range(of: "   "))

attributedString.addAttribute(.foregroundColor, value: UIColor.white, range: nsText.range(of: "World!"))
attributedString.addAttribute(.font, value: UIFont.systemFont(ofSize: 44.0), range: nsText.range(of: "World!"))

label.attributedText = attributedString
label.sizeToFit()

PlaygroundPage.current.liveView = label

CodePudding user response：

There is an attribute called expansion that adjusts the font's expansion factor using a float value. The problem only occurs where two ranges with different font sizes meet, and this is a graphical rendering issue that cannot be overridden. But if you explicitly zero out the expansion factor, or even apply a small negative value, the gaps will not be noticeable.

attributedString.addAttribute(.expansion, value: NSNumber(value: 0), range: nsText.range(of: "Hello   World!"))

https://developer.apple.com/documentation/foundation/nsattributedstring/key/1524652-expansion?language=objc__5