如何限制Swift中String或属性String中的字符数

Question

给定是一个带有x个字符的(html)字符串.String将被格式化为属性String.然后显示在UILabel.

在UILabel具有的高度>= 25和<= 50到行数限制为2.

由于String具有在格式化的属性String中不可见的字符,例如<b> / <i>,最好的方法是限制属性String的字符数.

UILabel财产.lineBreakMode = .byTruncatingTail导致词语被削减.

我们的目标,如果字符数将超过在空间的限制UILabel,是词与词之间切断.渴望maxCharacterCount = 50.确定space之前的最后一个maxCharacterCount.剪切字符串并追加...为最后一个字符UILabel.

限制角色的最佳方法是什么？帮助非常感谢.

Answer 1

从完整的字符串和标签的已知双线高度及其已知宽度开始,并在字符串末端保留切割字,直到在该宽度处,字符串的高度小于标签的高度.然后在末尾再剪一个单词以获得良好的度量,附加省略号,并将得到的字符串放入标签中.

就这样,我得到了这个:

请注意,"时间"之后的单词永远不会开始; 我们用插入的省略号停在一个精确的单词结尾处.这是我如何做到的:

    lab.numberOfLines = 2
    let s = "Little poltergeists make up the principle form of material " +
        "manifestation. Now is the time for all good men to come to the " +
        "aid of the country."
    let atts = [NSFontAttributeName: UIFont(name: "Georgia", size: 18)!]
    let arr = s.components(separatedBy: " ")
    for max in (1..<arr.count).reversed() {
        let s = arr[0..<max].joined(separator: " ")
        let attrib = NSMutableAttributedString(string: s, attributes: atts)
        let height = attrib.boundingRect(with: CGSize(width:lab.bounds.width, 
                                                      height:10000),
                                         options: [.usesLineFragmentOrigin],
                                         context: nil).height
        if height < lab.bounds.height {
            let s = arr[0..<max-1].joined(separator: " ") + "…"
            let attrib = NSMutableAttributedString(string: s, attributes: atts)
            lab.attributedText = attrib
            break
        }
    }

当然,可能是很多关于什么是"字",用于测量的条件更复杂,但上述说明了一般常用的技术为这样的事情,应该足以让你开始.

Answer 2

尝试这个：

import UIKit

class ViewController: UIViewController {
var str = "Hello, playground"
var thisInt = 10
@IBOutlet weak var lbl: UILabel!
var lblWidth : CGFloat = 0.0

override func viewDidLoad() {
    super.viewDidLoad()
    // Do any additional setup after loading the view, typically from a nib.
    lblWidth = lbl.bounds.width

    while str.characters.count <= thisInt - 3 {
        str.remove(at: str.index(before: str.endIndex))
        str.append("...")
    }
    lbl.text = str
}

override func didReceiveMemoryWarning() {
    super.didReceiveMemoryWarning()
    // Dispose of any resources that can be recreated.
}


}

字符串宽度计算链接