ios - NSAttributedString 在文本和背景前后带有填充

Question

我想使用 NSAttributedString 设置文本样式。文本应该有背景和自定义填充，以便文本到背景边缘有一点空间。

这就是我想要实现的目标:

这是我不想实现的目标(第二行的背景不是特定于单词/字符的):

这是我在 Playground 上尝试过的代码:

let quote = "some text with a lot of other text and \nsome other text."
let paragraphStyle = NSMutableParagraphStyle()
paragraphStyle.alignment = .left
let attributes: [NSAttributedString.Key: Any] = [
    NSAttributedString.Key.paragraphStyle: paragraphStyle,
    NSAttributedString.Key.backgroundColor: UIColor.red,
    NSAttributedString.Key.foregroundColor: UIColor.white
]
let attributedQuote = NSAttributedString(string: quote, attributes: attributes)

这就是 Playground 预览呈现的内容:

[![ Playground 预览][3]][3]

文本非常接近背景边缘。有什么办法可以让文本的背景有一些空间给文本吗？我需要一些填充物。我尝试使用 headIndent 但这会将带有背景的文本向右移动，而不仅仅是文本。因此它对填充没有用。

Answer 1

The text should have a background and a custom padding, so that the text has a little bit of space to the background's edge.

我找到的最好的方法是使用 TextKit，它有点麻烦，但它是完全模块化的，并且是为此目的而制作的。
在我看来，在其 draw 方法中绘制矩形不是由 TextView 本身决定的，那是 LayoutManager 的工作。

为了简化复制粘贴工作(Swift 5.1 - iOS 13)，项目中使用的所有类在下文中提供。

AppDelegate.swift 存储属性以在应用中的任何位置获取文本。

class AppDelegate: UIResponder, UIApplicationDelegate {

    lazy var TextToBeRead: NSAttributedString = {

        var text: String
        if let filepath = Bundle.main.path(forResource: "TextToBeRead", ofType: "txt") {
            do { text = try String(contentsOfFile: filepath) }
            catch { text = "E.R.R.O.R." }
        } else { text = "N.O.T.H.I.N.G." }

        return NSAttributedString(string: text)
    }()
}

ViewController.swift ⟹ 全屏只有一个 TextView 。

class ViewController: UIViewController, NSLayoutManagerDelegate {

    @IBOutlet weak var myTextView: UITextView!
    let textStorage = MyTextStorage()
    let layoutManager = MyLayoutManager()

    override func viewDidLoad() {
        super.viewDidLoad()

        self.layoutManager.delegate = self

        self.textStorage.addLayoutManager(self.layoutManager)
        self.layoutManager.addTextContainer(myTextView.textContainer)

        let appDelegate = UIApplication.shared.delegate as? AppDelegate
        self.textStorage.replaceCharacters(in: NSRange(location: 0, length: 0),
                                           with: (appDelegate?.TextToBeRead.string)!)
    }

    func layoutManager(_ layoutManager: NSLayoutManager,
                       lineSpacingAfterGlyphAt glyphIndex: Int,
                       withProposedLineFragmentRect rect: CGRect) -> CGFloat { return 20.0 }

    func layoutManager(_ layoutManager: NSLayoutManager,
                       paragraphSpacingAfterGlyphAt glyphIndex: Int,
                       withProposedLineFragmentRect rect: CGRect) -> CGFloat { return 30.0 }
}

MyTextStorage.swift

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)
    }
}

MyLayoutManager.swift

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 = 30.0

            let currentContext = UIGraphicsGetCurrentContext()
            currentContext?.saveGState()

            currentContext?.setStrokeColor(UIColor.red.cgColor)
            currentContext?.setLineWidth(1.0)
            currentContext?.stroke(lineRect)

            currentContext?.restoreGState()
        }
    }
}

...最后是这样的:

只有自定义颜色和调整几个参数以适应您的项目，但这是显示 NSAttributedString，在文本和背景前后填充 的基本原理...更多如果需要，不超过 2 行。