如何在iOS / Swift中为指定宽度创建固定宽度标签？

Question

Say I'm creating a calculator and I know I'm going to support a maximum of 20 digits in portrait and 40 digits in landscape.

How do I create or resize a label to display up to my maximum number of digits such that it doesn't keep resizing as we add or remove digits from the result?

Code I've tried so far;

let labelFont : UIFont = resultDigitsLabel.font;
let originalString : String = "00000000000000000000";
let nsString : NSString = originalString as NSString;
var labelSize : CGSize = nsString.size(attributes: [NSFontAttributeName: labelFont]);
labelSize.height = 0;
let labelRect : CGRect = resultDigitsLabel.frame;
let newFrame :CGRect = CGRect(origin: labelRect.origin, size: labelSize);
resultDigitsLabel.frame = newFrame;

resultDigitsLabel.layer.borderWidth = 0.5;
resultDigitsLabel.layer.cornerRadius = 5.0;

So far no luck, the original frame reset doesn't appear to resize the label and as I add or remove digits the frame (by watching the border) resizes also.

I don't have any size constraints that I see, should I be creating a constraint rather than setting the width by altering the frame?

Any other tips?

Thanks.

Answer 1

尝试将此属性添加到标签：-resultDigitsLabel.adjustsFontSizeToFitWidth = true

Answer 2

You have to calculate the frame for 20 digits or 40 digits and create the frame for UILabel with that frame.

let digits:NSString = "99999999999999999999" as NSString
let idealFrame= digits.boundingRect(with: CGSize(width: CGFloat.infinity, height: 30), options: .usesLineFragmentOrigin, attributes: [NSFontAttributeName:labelFont], context: nil).size

Now you can make UILabel this frame.

Answer 3

Constraint is the best way. Give Leading and Trailing constraint to your Label and also give equal width with the super view. It will support in both Landscape and Portrait mode.

Answer 4

As per thewarri0r9 above adding constraints did the trick;

    let screenSize: CGRect = UIScreen.main.bounds;
    let screenWidth = screenSize.width;
    let constraintMargin = (screenWidth - labelSize.width) / 2;
    let leadingConstraint = NSLayoutConstraint(item: targetDigitsLabel, attribute: .leading, relatedBy: .equal, toItem: view, attribute: .leading, multiplier: 1, constant: constraintMargin);
    let trailingConstraint = NSLayoutConstraint(item: targetDigitsLabel, attribute: .trailing, relatedBy: .equal, toItem: view, attribute: .trailing, multiplier: 1, constant: constraintMargin * -1);
    view.addConstraints([leadingConstraint, trailingConstraint]);