当 UILabel 的 numberoflines 为 0 时，.ByTruncatingHead 的工作方式与 truncatingmiddle 的方式相同

Question

重现此代码：

import UIKit
import PlaygroundSupport

class MyViewController : UIViewController {
    override func loadView() {
        let view = UIView()
        view.backgroundColor = .white

        let label = UILabel()
        label.frame = CGRect(x: 150, y: 200, width: 200, height: 70)
        label.lineBreakMode = .byTruncatingHead
        label.text = "Lorem Ipsum is simply dummy text of the printing and typesetting industry. Lorem Ipsum has been the industry's standard dummy text ever since the 1500s, when an unknown printer took a galley of type and scrambled it to make a type specimen book. It has survived not only five centuries, but also the leap into electronic typesetting, remaining essentially unchanged. It was popularised in the 1960s with the release of Letraset sheets containing Lorem Ipsum passages, and more recently with desktop publishing software like Aldus PageMaker including versions of Lorem Ipsum.Why do we use it?            It is a long established fact that a reader will be distracted by the readable content of a page when looking at its layout. The point of using Lorem Ipsum is that it has a more-or-less normal distribution of letters, as opposed to using 'Content here, content here', making it look like readable English. Many desktop publishing packages and web page editors now use Lorem Ipsum as their default model text, and a search for 'lorem ipsum' will uncover many web sites still in their infancy. Various versions have evolved over the years, sometimes by accident, sometimes on purpose (injected humour and the like).            Contrary to popular belief, Lorem Ipsum is not simply random text. It has roots in a piece of classical Latin literature from 45 BC, making it over 2000 years old. Richard McClintock, a Latin professor at Hampden-Sydney College in Virginia, looked up one of the more obscure Latin words, consectetur, from a Lorem Ipsum passage, and going through the cites of the word in classical literature, discovered the undoubtable source. Lorem Ipsum comes from sections 1.10.32 and 1.10.33 of ed since the 1500s is reproduced below for those interested. Sections 1.10.32 and 1.10.33 from de Finibus Bonorum et Malorum"
        label.numberOfLines = 0
        label.backgroundColor = .yellow
        label.textColor = .black
        
        view.addSubview(label)
        self.view = view
    }
}
// Present the view controller in the Live View window
PlaygroundPage.current.liveView = MyViewController()

问题是如何将多行文本头部剪裁为反对 linebreakmode 仅适用于最后一行？有解决这个 uikit 缺陷的方法吗？

Answer 1

规则是，使用截断策略，UILabel 会在词尾打断文本，然后，如果文本对于标签而言太长，最后一行行首、行中、行尾分别显示省略号，省略号处省略文字。

所以实际上您的代码的行为方式与 byTruncatingMiddle 不同，它将省略号放在最后一行的中间。您的代码将省略号放在最后一行的 start 处。

当 UILabel 的 numberoflines 为 0 时，.ByTruncatingHead 的工作方式与 truncatingmiddle 的方式相同

.ByTruncatingHead works the way truncatingmiddle should have when numberoflines is 0 for UILabel

uikit

uilabel

ios

swift