使用NSAttributedString将文本居中在UILabel中

Question

对我正在处理的应用程序进行一些基本改进。 iOS快速开发领域仍然是新手。我想我的代码中的文本行会自动居中，因为我将标签设置为居中。经过一番研究后，我发现事实并非如此。我如何将这样的代码与中心对齐：

let atrString = try NSAttributedString(
   data: assetDetails!.cardDescription.dataUsingEncoding(NSUTF8StringEncoding)!, 
   options: [NSDocumentTypeDocumentAttribute:NSHTMLTextDocumentType], 
   documentAttributes: nil)
assetDescription.attributedText = atrString

Answer 1

您需要创建指定中心对齐的段落样式，并将该段落样式设置为文本的属性。示例游乐场：

import UIKit
import PlaygroundSupport

let style = NSMutableParagraphStyle()
style.alignment = NSTextAlignment.center

let richText = NSMutableAttributedString(string: "Going through some basic improvements to a application I am working on. Still new to the iOS swift development scene. I figured that the lines of text in my code would automatically be centered because I set the label to center.",
                                         attributes: [ NSParagraphStyleAttributeName: style ])
// In Swift 4, use `.paragraphStyle` instead of `NSParagraphStyleAttributeName`.

let label = UILabel(frame: CGRect(x: 0, y: 0, width: 200, height: 400))
label.backgroundColor = UIColor.white
label.attributedText = richText
label.numberOfLines = 0
PlaygroundPage.current.liveView = label

结果：

由于您正在解析HTML文档以创建属性字符串，因此您需要在创建后添加该属性，如下所示：

let style = NSMutableParagraphStyle()
style.alignment = NSTextAlignment.center

let richText = try NSMutableAttributedString(
    data: assetDetails!.cardDescription.data(using: String.Encoding.utf8)!,
    options: [NSDocumentTypeDocumentAttribute:NSHTMLTextDocumentType],
    documentAttributes: nil)
richText.addAttributes([ NSParagraphStyleAttributeName: style ],
                       range: NSMakeRange(0, richText.length))
// In Swift 4, use `.paragraphStyle` instead of `NSParagraphStyleAttributeName`.
assetDescription.attributedText = richText

Swift 4的更新

在Swift 4中，属性名称现在是NSAttributeStringKey类型，标准属性名称是该类型的静态成员。所以你可以像这样添加属性：

richText.addAttribute(.paragraphStyle, value: style, range: NSMakeRange(0, richText.length))

Answer 2

在Swift 4.1中：

let style = NSMutableParagraphStyle()

style.alignment = NSTextAlignment.center

lbl.centerAttributedText = NSAttributedString(string: "Total Balance",attributes: [.paragraphStyle: style])

（为代码块编辑）

Answer 3

您可以使用此实用程序功能对标签进行所有常见配置

    @discardableResult
    public func DULabel(text: String, frame: CGRect = .zero, parent:UIView? = nil , font:UIFont, textColor:UIColor = .black, numOfLines:Int = 0 ,textAlignment: NSTextAlignment = .center,lineSpaceing:CGFloat = 0, cb: ((UILabel)->Void)? = nil  )-> UILabel! {
      let label = UILabel()
      label.frame = frame
      label.font = font
      label.textColor = textColor
      label.textAlignment = textAlignment
      label.numberOfLines = numOfLines
      if( lineSpaceing == 0 ){
        label.text = text
      }
      else {
        let paragraphStyle = NSMutableParagraphStyle()
        paragraphStyle.lineSpacing = lineSpaceing
        paragraphStyle.alignment = textAlignment
        let attrString = NSMutableAttributedString(string: text)
        attrString.addAttribute(.paragraphStyle, value:paragraphStyle, range:NSMakeRange(0, attrString.length))
        label.attributedText = attrString
      }
      if let parent = parent {
        parent.addSubview(label)
      }
      cb?(label)
      return label
    }