对标签尝试以下命令：

label.adjustsFontSizeToFitWidth = true
label.minimumScaleFactor = 0.2

并尝试将标签的行更改为0和1（检查两种情况）：

label.numberOfLines = 0 // or 1

MinimumScaleFactor的范围是0到1。因此，我们根据字体大小设置MinimumScaleFactor，如下所示

• • 目标C**

[lb setMinimumScaleFactor:10.0/[UIFont labelFontSize]];
lb.adjustsFontSizeToFitWidth = YES;

• • 雨燕3.0**

lb.minimumScaleFactor = 10/UIFont.labelFontSize
lb.adjustsFontSizeToFitWidth = true

我不知道这是否能完全回答您的问题，但是您可以使用此扩展来计算适合您自己的字体大小。
雨燕3

extension String {
   func height(constrainedBy width: CGFloat, with font: UIFont) -> CGFloat {
       let constraintSize = CGSize(width: width, height: .max)
       let boundingBox = self.boundingRectWithSize(constraintSize, options: .UsesLineFragmentOrigin, attributes: [NSFontAttributeName: font], context: nil)

       return boundingBox.height
   }

   func width(constrainedBy height: CGFloat, with font: UIFont) -> CGFloat {
       let constrainedSize = CGSize(width: .max, height: height)
       let boundingBox = self.boundingRectWithSize(constrainedSize, options: .UsesLineFragmentOrigin, attributes: [NSFontAttributeName: font], context: nil)

       return boundingBox.width
   }
}

• • 更新-向Swift 5添加示例并更新代码**

雨燕5

extension String {
    func height(constrainedBy width: CGFloat, with font: UIFont) -> CGFloat {
        let constraintRect = CGSize(width: width, height: .greatestFiniteMagnitude)
        let boundingBox = self.boundingRect(with: constraintRect, options: .usesLineFragmentOrigin, attributes: [NSAttributedStringKey.font: font], context: nil)

        return boundingBox.height
    }

    func width(constrainedBy height: CGFloat, with font: UIFont) -> CGFloat {
        let constrainedRect = CGSize(width: .greatestFiniteMagnitude, height: height)
        let boundingBox = self.boundingRect(with: constrainedRect, options: .usesLineFragmentOrigin, attributes: [NSAttributedStringKey.font: font], context: nil)

        return boundingBox.width
    }
}

我的逻辑是确保两个不同的标签具有相同的字体大小。在我的例子中，这是两个标签用于用户的名字和姓氏。我之所以需要两个标签，是因为每个标签都是独立的动画。

class ViewController: UIViewController {
      ...

      func viewDidLoad() {
         super.viewDidLoad()
         fixFontSizes()
         ...
      }

      func fixFontSizes() {
         let leadingMargin = self.leadingContainerConstraint.constant
         let trailingMargin = self.trailingContainerConstraint.constant
         let maxLabelWidth = self.view.bounds.width - leadingMargin - trailingMargin

         let firstName = self.firstNameLabel.text ?? ""
         let lastName = self.lastNameLabel.text ?? ""

         let firstNameWidth = firstName.width(constrainedBy: self.container.bounds.height, with: self.firstNameLabel.font)
         let lastNameWidth = lastName.width(constrainedBy: self.container.bounds.height, with: self.lastNameLabel.font)

         let largestLabelWidth = max(firstNameWidth, lastNameWidth)
         guard largestLabelWidth > maxLabelWidth else { return }

         let largestTextSize = max(self.firstNameLabel.font.pointSize, self.lastNameLabel.font.pointSize)

         let labelToScreenWidthRatio = largestLabelWidth / maxLabelWidth
         let calculatedMaxTextSize = floor(largestTextSize / labelToScreenWidthRatio)

         self.firstNameLabel.font = self.firstNameLabel.font.withSize(calculatedMaxTextSize)
         self.lastNameLabel.font = self.lastNameLabel.font.withSize(calculatedMaxTextSize)
      }

}

我只是做了你需要的，完美的作品！（仅编程）-我们正在设置大字体大小的标签，为了重新缩放到完美的字体大小。

self.label.font = UIFont(name: "Heiti TC", size: 60)
self.label.numberOfLines = 0
self.label.minimumScaleFactor = 0.1
self.label.baselineAdjustment = .alignCenters
self.label.textAlignment  = .center

如果使用AutoLayout，请在viewDidLayoutSubviews中实现此代码（布局完成后）。
你的，罗伊

上述Swift 4转换：

extension String
{
    func height(constrainedBy width: CGFloat, with font: UIFont) -> CGFloat
    {
        let constraintSize = CGSize(width: width, height: .greatestFiniteMagnitude)
        let boundingBox = self.boundingRect(with: constraintSize, options: .usesLineFragmentOrigin, attributes: [NSAttributedStringKey.font: font], context: nil)

        return boundingBox.height
    }

    func width(constrainedBy height: CGFloat, with font: UIFont) -> CGFloat
    {
        let constrainedSize = CGSize(width: .greatestFiniteMagnitude, height: height)
        let boundingBox = self.boundingRect(with: constrainedSize, options: .usesLineFragmentOrigin, attributes: [NSAttributedStringKey.font: font], context: nil)

        return boundingBox.width
    }
}

雨燕5

extension String
{
    func height(constrainedBy width: CGFloat, with font: UIFont) -> CGFloat
    {
        let constraintSize = CGSize(width: width, height: .greatestFiniteMagnitude)
        let boundingBox = self.boundingRect(with: constraintSize, options: .usesLineFragmentOrigin, attributes: [NSAttributedString.Key.font: font], context: nil)

        return boundingBox.height
    }

    func width(constrainedBy height: CGFloat, with font: UIFont) -> CGFloat
    {
        let constrainedSize = CGSize(width: .greatestFiniteMagnitude, height: height)
        let boundingBox = self.boundingRect(with: constrainedSize, options: .usesLineFragmentOrigin, attributes: [NSAttributedString.Key.font: font], context: nil)

        return boundingBox.width
    }
}

这里有一个黑客解决方案：

var size: CGFloat = 20

    while titleLabel.frame.width > containerView.frame.width {

        titleLabel.font = UIFont.systemFont(ofSize: size)
        titleLabel.sizeToFit()
        size -= 1

    }