ios - SWIFT:让画外音停止阅读截断的字符串

Question

在一个标签中，我赋予一个大字符串并设置它的 .lineBreakMode = .buTrucatingTail，但是当我这样做并尝试在其上使用 VoiceOver 时，我最终读取了整个字符串，而不是只是屏幕上的内容，这里是一个例子:

string.text = "Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat. Duis aute irure dolor in reprehenderit in voluptate velit esse cillum dolore eu fugiat nulla pariatur. Excepteur sint occaecat cupidatat non proident, sunt in culpa qui officia deserunt mollit anim id est laborum."
srring.lineBreakMode = .buTrucatingTail

这是屏幕上显示的内容:

Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco...

但是画外音读出了整个字符串。

有谁知道如何让它停在截断的三个点上？或者如何将辅助功能标签设置为屏幕上的内容(因为文本长度会根据设备而变化)？

提前致谢。

Answer 1

[...] when I do that and try to use VoiceOver on it, I ends up reading the whole string, not just what is in the screen [...] voice over reads the whole string.

正如我在评论中所说，截断只是为了显示。
VoiceOver 将始终读出字符串的整个文本，它不关心屏幕上显示的内容。
它与accessibilityLabel完全一样，可能与显示的内容不同:这里的accessibilityLabel是整个字符串内容。 🤨

Does anyone know how to make it stop in the truncation three dots?

你的问题引起了我的好奇心，我决定研究这个问题。
我找到了一个使用 TextKit 的解决方案，其基础知识应该是已知的:如果不是这样的话 ⟹ Apple doc 👍

⚠️ 主要思想是确定最后一个可见字符的索引，以便提取显示的子字符串，最后将其分配给accessibilityLabel。 ⚠️

初始假设:使用与问题 (byTruncationTail) 中定义的相同 lineBreakMode 的 UILabel。
我在 Playground 上编写了以下整个代码，并使用 Xcode 空白项目检查了结果。🤓

import Foundation
import UIKit

extension UILabel {
    var displayedLines: (number: Int?, lastIndex: Int?) {
    
        guard let text = text else {
            return (nil, nil)
        }
    
    let attributes: [NSAttributedString.Key: UIFont] = [.font:font]
    let attributedString = NSAttributedString(string: text,
                                              attributes: attributes)
    
    //Beginning of the TextKit basics...
    let textStorage = NSTextStorage(attributedString: attributedString)
    let layoutManager = NSLayoutManager()
    textStorage.addLayoutManager(layoutManager)
    
    let textContainerSize = CGSize(width: frame.size.width,
                                   height: CGFloat.greatestFiniteMagnitude)
    let textContainer = NSTextContainer(size: textContainerSize)
    textContainer.lineFragmentPadding = 0.0 //Crucial to get the most accurate results.
    textContainer.lineBreakMode = .byTruncatingTail
    
    layoutManager.addTextContainer(textContainer)
    //... --> end of the TextKit basics
    
    var glyphRangeMax = NSRange()
    let characterRange = NSMakeRange(0, attributedString.length)
    //The 'glyphRangeMax' variable will store the appropriate value thanks to the following method.
    layoutManager.glyphRange(forCharacterRange: characterRange,
                             actualCharacterRange: &glyphRangeMax)
    
    print("line : sentence -> last word")
    print("----------------------------")
    
    var truncationRange = NSRange()
    var fragmentNumber = ((self.numberOfLines == 0) ? 1 : 0)
    var globalHeight: CGFloat = 0.0
    
    //Each line fragment of the layout manager is enumerated until the truncation is found.
    layoutManager.enumerateLineFragments(forGlyphRange: glyphRangeMax) { rect, usedRect, textContainer, glyphRange, stop in
        
        globalHeight += rect.size.height
        
        if (self.numberOfLines == 0) {
            if (globalHeight > self.frame.size.height) {
                print("⚠️ Constraint ⟹ height of the label ⚠️")
                stop.pointee = true //Stops the enumeration and returns the results immediately.
            }
        } else {
            if (fragmentNumber == self.numberOfLines) {
                print("⚠️ Constraint ⟹ number of lines ⚠️")
                stop.pointee = true
            }
        }
        
        if (stop.pointee.boolValue == false) {
            fragmentNumber += 1
            truncationRange = NSRange()
            layoutManager.characterRange(forGlyphRange: NSMakeRange(glyphRange.location, glyphRange.length),
                                         actualGlyphRange: &truncationRange)
            
            let sentenceInFragment = self.sentenceIn(truncationRange)
            let line = (self.numberOfLines == 0) ? (fragmentNumber - 1) : fragmentNumber
            print("\(line) : \(sentenceInFragment) -> \(lastWordIn(sentenceInFragment))")
        }
    }
    
    let lines = ((self.numberOfLines == 0) ? (fragmentNumber - 1) : fragmentNumber)
    return (lines, (truncationRange.location + truncationRange.length - 2))
}

//Function to get the sentence of a line fragment
func sentenceIn(_ range: NSRange) -> String {
    
    var extractedString = String()
    
    if let text = self.text {
        
        let indexB = text.index(text.startIndex,
                                offsetBy:range.location)
        let indexF = text.index(text.startIndex,
                                offsetBy:range.location+range.length)
        
        extractedString = String(text[indexB..<indexF])
    }
    return extractedString
}
}


//Function to get the last word of the line fragment
func lastWordIn(_ sentence: String) -> String {

    var words = sentence.components(separatedBy: " ")
    words.removeAll(where: { $0 == "" })

    return (words.last == nil) ? "o_O_o" : (words.last)!
}

完成后，我们需要创建标签:

let labelFrame = CGRect(x: 20,
                        y: 50,
                        width: 150,
                        height: 100)
var testLabel = UILabel(frame: labelFrame)
testLabel.text = "Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat. Duis aute irure dolor in reprehenderit in voluptate velit esse cillum dolore eu fugiat nulla pariatur. Excepteur sint occaecat cupidatat non proident, sunt in culpa qui officia deserunt mollit anim id est laborum."

...并测试代码:

testLabel.numberOfLines = 3

if let _ = testLabel.text {
    let range = NSMakeRange(0,testLabel.displayedLines.lastIndex! + 1)
    print("\nNew accessibility label to be implemented ⟹ \"\   (testLabel.sentenceIn(range))\"")
}

playground 的调试区用 3 行显示结果: ...如果想要“尽可能多的行”，我们会得到: 这似乎运作良好。 🥳

将此原理包含到您自己的代码中，您将能够让 VoiceOver 朗读屏幕上显示的标签的截断内容。 🎊🎉