UILabel 字体大小与 UIView 帧大小一致

我不能肯定地说，因为很难完全理解一些变量像什么。vv

但是，我认为获得断断续续的结果的主要问题可能是：

1. 计算当前帧字体的方式有问题
2. 似乎您只在手势有时调整字体，而我认为即使它正在调整，它也很有用endedchanged

一种方法是按照以下步骤操作：

1. 获取视图的新边界（主要是宽度和高度）
2. 为标签指定最大字体大小
3. 继续缩小字体，直到获得适合视图新大小的字体

这将很容易，如果文本不是太大，应该可以工作

在我自己做了一些研究之后，因为这是一个有趣的问题，我遇到了一些优雅的解决方案，可以使用二进制搜索找到最佳字体大小

因此，我是这样实现的：

1. 名为 FlexiFontLabel 的自定义 UILabel 子类

逻辑在评论中进行了解释

class FlexiFontLabel: UILabel
{
    // Boundary of minimum and maximum
    private let maxFontSize = CGFloat(500)
    private let minFontSize = CGFloat(5)
    
    // Margin of error is needed in binary search
    // so we can return when reach close enough
    private let marginOFError = CGFloat(0.5)
    
    // layoutSubviews() will get called while updating
    // font size so we want to lock adjustments if
    // processing is already in progress
    private var isUpdatingFontSize = false
    
    // Once this is set to true, the label should only
    // only support multiple lines rather than one
    var doesAdjustFontSizeToFitFrame = false
    {
        didSet
        {
            if doesAdjustFontSizeToFitFrame
            {
                numberOfLines = 0
            }
        }
    }
    
    // Adjusting the frame of the label automatically calls this
    override func layoutSubviews()
    {
        super.layoutSubviews()
        
        // Make sure the label is set to auto adjust the font
        // and it is not currently processing the font size
        if doesAdjustFontSizeToFitFrame
            && !isUpdatingFontSize
        {
            adjustFontSizeIfRequired()
        }
    }
    
    
    /// Adjusts the font size to fit the label's frame using binary search
    private func adjustFontSizeIfRequired()
    {
        guard let currentText = text,
              var currentFont = font else
        {
            print("failed")
            return
        }
        
        // Lock function from being called from layout subviews
        isUpdatingFontSize = true
        
        // Set max and min font sizes
        var currentMaxFontSize = maxFontSize
        var currentMinFontSize = minFontSize
        
        while true
        {
            // Binary search between min and max
            let midFontSize = (currentMaxFontSize + currentMinFontSize) / 2;
            
            // Exit if approached minFontSize enough
            if (midFontSize - currentMinFontSize <= marginOFError)
            {
                // Set min font size and exit because we reached
                // the biggest font size that fits
                currentFont = UIFont(name: currentFont.fontName,
                                     size: currentMinFontSize)!
                
                break;
            }
            else
            {
                // Set the current font size to the midpoint
                currentFont = UIFont(name: currentFont.fontName,
                                     size: midFontSize)!
            }
            
            // Configure an attributed string which can be used to find an
            // appropriate rectangle for a font size using its boundingRect
            // function
            let attribute = [NSAttributedString.Key.font: currentFont]
            let attributedString = NSAttributedString(string: currentText,
                                                      attributes: attribute)
            
            let options: NSStringDrawingOptions = [.usesLineFragmentOrigin,
                                                   .usesFontLeading]
            
            // Get a bounding box with the width of the current label and
            // an unlimited height
            let constrainedSize = CGSize(width: frame.width,
                                         height: CGFloat.greatestFiniteMagnitude)
            
            // Get the appropriate rectangle for the text using the current
            // midpoint font
            let newRect = attributedString.boundingRect(with: constrainedSize,
                                                        options: options,
                                                        context: nil)
            
            // Get the current area of the new rect and the current
            // label's bounds
            let newArea = newRect.width * newRect.height
            let currentArea = bounds.width * bounds.height
            
            // See if the new frame is lesser than the current label's area
            if newArea < currentArea
            {
                // The best font size is in the bigger half
                currentMinFontSize = midFontSize + 1
            }
            else
            {
                // The best font size is in the smaller half
                currentMaxFontSize = midFontSize - 1
            }
        }
        
        // set the font of the current label
        font = currentFont
        
        // Open label to be adjusted again
        isUpdatingFontSize = false
    }
}

2. 标签的使用方法

这就像通过一个小的添加来设置任何 UILabel

let label = FlexiFontLabel()
/// Do all your set up like frames, colors
// alignments etc

// This opens the label to auto adjust itself
label.doesAdjustFontSizeToFitFrame = true

3. 平移手势实现 这里没有发生任何有趣的事情，因为所有的调整都发生在 UILabel 子类中，但我只想向你展示我为更好地理解所做的工作

@objc
func scaleGesture(recognizer: UIPanGestureRecognizer)
{
    let location = recognizer.location(in: view)
    
    // This is my logic to prevent the bottom right anchor going
    // below a certain threshold, you can ignore it as it has
    // nothing to do with your solution
    if location.x >= minX && location.y >= minY
    {
        // Update the position of the anchor
        circle.center = location
        
        // Calculate the new frame for the label
        var newLabelFrame = label.frame
        let newWidth = location.x - originalLabelFrame.origin.x
        let newHeight = location.y - originalLabelFrame.origin.y
        newLabelFrame.size = CGSize(width: newWidth,
                                    height: newHeight)
        
        // After updating the label, layoutSubviews() will be called
        // automatically which will update the font size
        label.frame = newLabelFrame
    }
}

这给了我以下结果，当根据标签框更改字体大小时，该结果非常流畅