UILabel doesn't update after setting attributedText

Question

I use MapKit to record running distance. I have the following code:

var runningDistance : Double = 0{
    didSet{
        guard let text = runningDistanceLabel.attributedText as? NSMutableAttributedString else{return}
        let range = NSMakeRange(0, 4)            
        let attributeString = NSAttributedString(string: String(format:"%.2f",runningDistance/1000.0), attributes: [
            NSFontAttributeName:UIFont(name: "DINCondensed-Bold", size: 17)!       
            ])
        text.replaceCharacters(in: range, with: attributeString)
        runningDistanceLabel.attributedText = text

        print(runningDistanceLabel.text)
        print(runningDistanceLabel.attributedText)            
    }
}

When userLocation update, I calculate the distance and set runningDistance.

In console：

Optional("0.04公里")
Optional(0.04{
    NSFontAttributeName = "Optional(<UICTFont: 0x7ff79b7b7250> font-family: \"DIN Condensed\"; font-weight: bold; font-style: normal; font-size: 17.00pt)";
}公里{
    NSFont = "<UICTFont: 0x7ff79d800110> font-family: \".PingFangSC-Regular\"; font-weight: normal; font-style: normal; font-size: 14.00pt";
NSParagraphStyle = "Alignment 2, LineSpacing 0, ParagraphSpacing 0, ParagraphSpacingBefore 0, HeadIndent 0, TailIndent 0, FirstLineHeadIndent 0, LineHeight 0/0, LineHeightMultiple 0, LineBreakMode 4, Tabs (\n    28L,\n    56L,\n    84L,\n    112L,\n    140L,\n    168L,\n    196L,\n    224L,\n    252L,\n    280L,\n    308L,\n    336L\n), DefaultTabInterval 0, Blocks (\n), Lists (\n), BaseWritingDirection -1, HyphenationFactor 0, TighteningForTruncation NO, HeaderLevel 0";
})

That shows the runningDistanceLabel's text and attributedText has been set and changed. But in simulator, the label's text remains unchanged.

And if I replace:

runningDistanceLabel.attributedText = text

with:

runningDistanceLabel.text = "\(runningDistance)"

Then in simulator, the label's text can be changed normally.

What's wrong with my code about setting attributedText? How to set attributedText and update correctly in simulator?

Thank you very much!

Edit:

I am sure the guard has been passed because it has printed label's text and attributedText in console and I have added a breakpoint to test it.

I also try:

DispatchQueue.main.async {[unowned self] in
    self.runningDistanceLabel.attributedText = text
}

But I still cannot update the label's text.

Soluion

And with Rroobb's help, I add a line of code to set label's text before setting its attributedText:

runningDistanceLabel.text = String(format:"%.2f",runningDistance/1000.0) + "公里"
runningDistanceLabel.attributedText = text

And in simulator, the label's text can be updated now. Amazing!

In iOS document about UILabel's attributedText:

Assigning a new value to this property also replaces the value of the text property with the same string data, albeit without any formatting information.

It seems that setting attributedText can automatically change the text property.

But here I don't know why I should set text before setting attributedText in order to update the label's text.

Answer 1

This works, I added two line of code :

 var runningDistance : Double = 0.0 {
    didSet{
        guard let text = runningDistanceLabel.attributedText as? NSMutableAttributedString else{

            return

        }

        let range = NSMakeRange(0, 4)
        runningDistanceLabel.text = String(format:"%.2f",runningDistance/1000.0) //here
        runningDistanceLabel.font = UIFont(name: "DINCondensed-Bold", size: 17) // here
        let attributeString = NSAttributedString(string: String(format:"%.2f",runningDistance/1000.0), attributes: [
            "NSFontAttributeName":UIFont(name: "DINCondensed-Bold", size: 17)!
            ])

        text.replaceCharacters(in: range, with: attributeString)
        runningDistanceLabel.attributedText = text


        print(runningDistanceLabel.text!)
        print(runningDistanceLabel.attributedText!)
    }
}