默认布局管理器填充没有文本(最后一行除外)的背景颜色(通过 NSAttributedString .backgroundColor 属性指定)。
我已经通过子类化 NSLayoutManager 并覆盖 func drawBackground(forGlyphRange glyphsToShow: NSRange, at origin: CGPoint) 来实现我想要的效果，如下所示:
override func drawBackground(forGlyphRange glyphsToShow: NSRange, at origin: CGPoint) {
guard let textContainer = textContainers.first, let textStorage = textStorage else { fatalError() }
// This just takes the color of the first character assuming the entire container has the same background color.
// To support ranges of different colours, you'll need to draw each glyph separately, querying the attributed string for the
// background color attribute for the range of each character.
guard textStorage.length > 0, let backgroundColor = textStorage.attribute(.backgroundColor, at: 0, effectiveRange: nil) as? UIColor else { return }
var lineRects = [CGRect]()
// create an array of line rects to be drawn.
enumerateLineFragments(forGlyphRange: glyphsToShow) { (_, usedRect, _, range, _) in
var usedRect = usedRect
let locationOfLastGlyphInLine = NSMaxRange(range)-1
// Remove the space at the end of each line (except last).
if self.isThereAWhitespace(at: locationOfLastGlyphInLine) {
let lastGlyphInLineWidth = self.boundingRect(forGlyphRange: NSRange(location: locationOfLastGlyphInLine, length: 1), in: textContainer).width
usedRect.size.width -= lastGlyphInLineWidth
}
lineRects.append(usedRect)
}
lineRects = adjustRectsToContainerHeight(rects: lineRects, containerHeight: textContainer.size.height)
for (lineNumber, lineRect) in lineRects.enumerated() {
guard let context = UIGraphicsGetCurrentContext() else { return }
context.saveGState()
context.setFillColor(backgroundColor.cgColor)
context.fill(lineRect)
context.restoreGState()
}
}
private func isThereAWhitespace(at location: Int) -> Bool {
return propertyForGlyph(at: location) == NSLayoutManager.GlyphProperty.elastic
}
但是，这不能处理属性字符串中由范围指定的多种颜色的可能性。我怎样才能做到这一点？我看过 fillBackgroundRectArray 却收效甚微。
How might I achieve this?
这是我如何达到您的目标，在著名的 Lorem ipsum... 中以不同颜色突出显示 “sit” 术语，该术语足以在多个测试中进行测试行。
支持以下代码的所有基础(Swift 5.1，iOS 13)在 this answer 中提供为清楚起见，不会在此处复制⟹它们导致了结果1。
在您的情况下，您想突出显示字符串的某些特定部分，这意味着这些元素由于其内容而应具有专用的关键属性⟹在我看来，这取决于 textStorage 来处理用它。
MyTextStorage.swift
// Sent when a modification appears via the 'replaceCharacters' method.
override func processEditing() {
var regEx: NSRegularExpression
do {
regEx = try NSRegularExpression.init(pattern: " sit ", options: .caseInsensitive)
let stringLength = backingStorage.string.distance(from: backingStorage.string.startIndex,
to: backingStorage.string.endIndex)
regEx.enumerateMatches(in: backingStorage.string,
options: .reportCompletion,
range: NSRange(location: 1, length: stringLength-1)) { (result, flags, stop) in
guard let result = result else { return }
self.setAttributes([NSAttributedString.Key.foregroundColor : UIColor.black, //To be seen above every colors.
NSAttributedString.Key.backgroundColor : UIColor.random()],
range: result.range)
}
} catch let error as NSError {
print(error.description)
}
super.processEditing()
}
}
//A random color is provided for each " sit " element to highlight the possible different colors in a string.
extension UIColor {
static func random () -> UIColor {
return UIColor(red: CGFloat.random(in: 0...1),
green: CGFloat.random(in: 0...1),
blue: CGFloat.random(in: 0...1),
alpha: 1.0)
}
}
如果你从这里构建并运行，你会得到结果 2 显示文本中 "sit" 的每个彩色背景都有问题 ⟹ 有一个偏移量lineFragment 和彩色背景矩形之间。
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