NSAttributedText not working for UILabel in Swift - swift

Question

I'm using Swift 3 on an iOS 10.3 iPhone 6s.
I have an extension method on NSAttributedString:
extension NSAttributedString {
class func attributedString(title: String, titleFont: UIFont, body: String, bodyFont: UIFont) -> NSAttributedString {
let titleAttributes = [NSFontAttributeName : titleFont]
let bodyAttributes = [NSFontAttributeName : bodyFont]
let title = NSAttributedString(string: "\(title): ", attributes: titleAttributes)
let body = NSAttributedString(string: "\(body)", attributes: bodyAttributes)
let text = NSMutableAttributedString()
text.append(title)
text.append(body)
return text
}
}
And I have this UITableViewCell configure method that gets called when setting up the cell in cellForRowAtIndexPath:
class MyCustomCell: UITableViewCell {
...
func configure() {
...
myLabel.attributedText = NSAttributedString.attributedString(title: t, titleFont: tFont, body: b, bodyFont: bFont)
}
}
Somehow the label is blank on the screen.
The params are not optional (in other words, t and b are not and cannot be nil).
If I tap the cell, it opens a screen and then when I come back, the label is showing the text correctly. I've tried adding things like myLabel.setNeedsDisplay(), setNeedsDisplay(), setNeedsLayout(), etc. to the end of the configure method, but nothing's working.
What am I doing wrong?
Other attributed string issues have been because people used things like regular NSFontAttributeName with the documentAttributes: init method. That's not what I'm doing here.
UPDATE:
If I pause with the debugger to inspect the UI, here's what the label shows:
<UILabel: 0x1041734b0; frame = (20 0; 297 0); text = 'Title: body'; opaque = NO; autoresize = RM+BM; userInteractionEnabled = NO; layer = <_UILabelLayer: 0x174298290>>
I don't understand why it's got a height of 0. The label's vertical content hugging and content compression resistance priorities are set to 1000 in the storyboard, which normally works great when I use a UILabel's text property. Maybe the vertical hugging and compression resistance priorities don't work correctly with attributed text?
UPDATE 2:
I just changed the constraints by setting the label's vertical content hugging and content compression resistance priorities back to default and giving the label a height constraint of 20. Now the label shows correctly!
I don't like this solution because I want the label to automatically have a height of 0 if there is no text and, if there is text, I want the label's height to match the font size (which can vary depending on user preference's in my app). In other words, I don't want to have to manage the label's height constraint.
Update 3:
Something I didn't show in my configure method...at the beginning I have a guard statement where I clear the label's attributed text if there's no title or body to show. My goal is for the label to hide. However, if there's a title and body, then I proceed to the line I showed in the configure method above.
When I remove this line in the guard statement, the label is visible with a valid height. The behavior is the same when I use the label's text property, which I didn't realize.
I tried using setNeedsLayout() and layoutIfNeeded() to reload the label so it would set its size correctly when I give it text, but it's not working.
Summary
I want to be able to set the vertical content hugging and content compression resistance priorities to 1000 from the storyboard so that the label's height depends on its content. And when I set the label's attributedText to nil, or "", or "Title: body", I want it to automatically set its height correctly. Is this possible? Am I misunderstanding the content priorities?

Answer 1

I see you got it solved, but thought I'd put this here for anyone else stumbling on this.
Remember when updating the UI to always do it on the main thread. When you reload the cell in cellForRowAtIndexPath I believe your code is being called on the main thread.
When you call it elsewhere, it's a good idea to do it like so:
dispatchQueue.main.async {
configure()
}

Answer 2

So it turns out that my problem was that I was also calling configure from the view controller outside of the context of the cellForRowAtIndexPath: method, and it wasn't reloading the cell's height (even though the label's height had changed since I had set text on it).
So, I needed to add code to reload the cell in the table view:
NSIndexPath *indexPath = ...; // Get index path for the cell I want to update.
VCInboxCell *cell = (MyCustomCell *) [self.table cellForRowAtIndexPath:indexPath];
if (cell) {
[cell configure];
[self.conversationsTable reloadRowsAtIndexPaths:#[indexPath] withRowAnimation:UITableViewRowAnimationNone];
}
In other words, I was setting up the cell with configure in cellForRowAtIndexPath:, but at that point the label's text was nil (because the model's data for the label wasn't set yet). Then, when the model's data changed for the label, I was calling configure again, but not updating the row, so the label was being squashed due to constraints in the cell, even though it wanted to have a height of 19.5 according to its intrinsicContentSize (based on its text value).
Reloading the cell updates the height and all is well.