设置为自动换行时如何获取UILabel文本的实际宽度

Question

I have the following code to set up a UILabel:

let label = UILabel()
label.numberOfLines = 0
label.textAlignment = .center
label.lineBreakMode = .byWordWrapping
label.preferredMaxLayoutWidth = maxWidth

label.text = "String that is long enough to cause word wrap."

label.sizeToFit()
self.view.addSubview(label)

The result that I need is for the label to wrap the text as it would once it reaches label.preferredMaxLayoutWidth then actually size itself to just wide enough to fit the wrapped text. Here's a diagram to illustrate:

The red box's width is equal to label.preferredMaxLayoutWidth and that is the actual size I am getting with my code above. The black box is the size that I would like it to be. Whether the label was sized to the red or black, the word wrapping would be the same.

So, how can I resize my label to be the smallest possible width while maintaining the current word wrap?

Edit:

Although constraints might be the usual option, in my case, I don't think it is because I am sizing my superview according to the resulting size of this label.

Answer 1

Ok, I just figured it out. @rmaddy was correct in the question's comments above. I had seen boundingRectWithSize:options:attributes:context: before asking the question, but had issues figuring it out in swift. But now I've got it. Here is my updated code:

let label = UILabel()

    let text = "String that is long enough to cause word wrap."
    let rect = text.boundingRect(with: CGSize(width: maxDesiredWidth, height:CGFloat.greatestFiniteMagnitude), options: NSStringDrawingOptions.usesLineFragmentOrigin, attributes: nil, context: nil)

    label.numberOfLines = 0
    label.textAlignment = .center
    label.lineBreakMode = .byWordWrapping
    label.frame = rect

    label.text = text

    label.sizeToFit()
    self.view.addSubview(label)