我希望下划线像任何其他正常的下划线机制一样位于文本下方。但是，对于 NSAttributed 字符串，它会留下带有“g's”和“y's”的孔
示例：
应该是什么样子：
如何增加下划线和标签之间的间距？
【问题讨论】：
标签： ios nsattributedstring underline
你可以使用 UITextView 我在 NSLayoutManager 中添加了自定义 NSAttributedStringKey "customUnderline" 和 swizzling 方法 drawUnderline。
import Foundation
import SwiftyAttributes
import UIKit
private let swizzling: (AnyClass, Selector, Selector) -> Void = { forClass, originalSelector, swizzledSelector in
guard let originalMethod = class_getInstanceMethod(forClass, originalSelector),
let swizzledMethod = class_getInstanceMethod(forClass, swizzledSelector) else {
return
}
method_exchangeImplementations(originalMethod, swizzledMethod)
}
extension NSAttributedStringKey {
static var customUnderline: NSAttributedStringKey = NSAttributedStringKey("customUnderline")
}
extension Attribute {
static var customUnderline: Attribute = Attribute.custom(NSAttributedStringKey.customUnderline.rawValue, true)
}
extension NSLayoutManager {
// MARK: - Properties
static let initSwizzling: Void = {
let originalSelector = #selector(drawUnderline(forGlyphRange:underlineType:baselineOffset:lineFragmentRect:lineFragmentGlyphRange:containerOrigin:))
let swizzledSelector = #selector(swizzled_drawUnderline(forGlyphRange:underlineType:baselineOffset:lineFragmentRect:lineFragmentGlyphRange:containerOrigin:))
swizzling(NSLayoutManager.self, originalSelector, swizzledSelector)
}()
// MARK: - Functions
@objc
func swizzled_drawUnderline(forGlyphRange glyphRange: NSRange, underlineType underlineVal: NSUnderlineStyle, baselineOffset: CGFloat, lineFragmentRect lineRect: CGRect, lineFragmentGlyphRange lineGlyphRange: NSRange, containerOrigin: CGPoint) {
guard needCustomizeUnderline(underlineType: underlineVal) else {
swizzled_drawUnderline(forGlyphRange: glyphRange,
underlineType: underlineVal,
baselineOffset: baselineOffset,
lineFragmentRect: lineRect,
lineFragmentGlyphRange: lineGlyphRange,
containerOrigin: containerOrigin)
return
}
let heightOffset = containerOrigin.y - 1 + (getFontHeight(in: glyphRange) ?? (lineRect.height / 2))
drawStrikethrough(forGlyphRange: glyphRange,
strikethroughType: underlineVal,
baselineOffset: baselineOffset,
lineFragmentRect: lineRect,
lineFragmentGlyphRange: lineGlyphRange,
containerOrigin: CGPoint(x: containerOrigin.x,
y: heightOffset))
}
// MARK: - Private functions
private func needCustomizeUnderline(underlineType underlineVal: NSUnderlineStyle) -> Bool {
guard underlineVal == NSUnderlineStyle.styleSingle else {
return false
}
let attributes = textStorage?.attributes(at: 0, effectiveRange: nil)
guard let isCustomUnderline = attributes?.keys.contains(.customUnderline), isCustomUnderline else {
return false
}
return true
}
private func getFontHeight(in glyphRange: NSRange) -> CGFloat? {
let location = characterRange(forGlyphRange: glyphRange, actualGlyphRange: nil).location
guard let font = textStorage?.attribute(.font, at: location, effectiveRange: nil) as? UIFont else {
return nil
}
return font.capHeight
}
}
【讨论】：
没有办法用NSAttributedString 或CoreText 来控制这种行为（除了自己画下划线）。 NSAttributedString 对此没有选择（和CoreText hasn't got one, either）。
在 Apple 系统上，第一个版本（有差距）是“预期的”行为，因为它是 Apple 提供并在整个系统（以及 Safari、TextEdit 等应用程序）中使用的行为。
如果你真的，真的想有没有间隙的下划线，你需要画没有下划线的字符串，然后自己画线（我需要这样做in one of my projects and I can tell you it's hard；参见this file，搜索“下划线” )。
【讨论】：
我添加了一条线（UIView），高度为 1，宽度类似于标签，与 UILabel 的底部对齐。
let label = UILabel()
label.text = "underlined text"
let spacing = 2 // will be added as negative bottom margin for more spacing between label and line
let line = UIView()
line.translatesAutoresizingMaskIntoConstraints = false
line.backgroundColor = label.textColor
label.addSubview(line)
label.addConstraints(NSLayoutConstraint.constraints(withVisualFormat: "H:|[line]|", metrics: nil, views: ["line":line]))
label.addConstraints(NSLayoutConstraint.constraints(withVisualFormat: "V:[line(1)]-(\(-spacing))-|", metrics: nil, views: ["line":line]))
【讨论】：