IOS/Objective-C: MakeUILabel Flow to Multiple Lines with Autolayout - ios

Question

I am trying to get a UILabel to flow to multiple lines and push the elements below it downwards using autolayout.
Here is my code called in viewwillappear.
self.myLabel.numberOfLines = 0;
self.myLabel.lineBreakMode = NSLineBreakByWordWrapping;
[_myLabel setContentCompressionResistancePriority:1000
forAxis:UILayoutConstraintAxisVertical];
[self.myLabel setNeedsDisplay];
[self.myLabel layoutIfNeeded];
[self.view setNeedsDisplay];
[self.view layoutIfNeeded];
The UILabel is constrained at the top to the content view and the image below it is constrained to the bottom of the UILabel. The label also has a height constraint of >=21.
On initial load, the label only shows one line.
The weird thing is that after launching a modal VC and the closing it, the label does go to multiple lines but fails to push down the elements below it.
On initial load.
After launching and canceling modal VC
I am wondering if the problem has something to do with timing of laying out subviews but have tried almost every thing.
Thanks in advance for any suggestions.

Answer 1

Simple example:
Create a new ViewController.
Add a button, constrain 40-pts from the top and centered horizontally
Add a UIView (green view). Constrain centered horizontally, width of 240, and top-space to button of 20.
Add two labels to the green view.
Top label, number of lines = 0, leading and trailing constraints of 16, top constraint of 8 (to green superview)
Bottom label, centered horizontally, top space to Top label of 8, bottom constraint of 8 (to green superview).
Connect the Top label to #IBOutlet var multiLineLabel: UILabel! in the view controller.
Connect the button touch-up-inside to the #IBAction func didTap(_ sender: Any) function in the view controller.
NO CHANGES to priorities.
Run the app. Each tap of the button will add text to the top / multi-line label, and it will "push down" the bottom label, which will, in turn, "push down" the bottom edge of the green view.
class ExpandingLabelViewController: UIViewController {
#IBOutlet var multiLineLabel: UILabel!
#IBAction func didTap(_ sender: Any) {
if let s = multiLineLabel.text {
multiLineLabel.text = s + " Here is some more text."
}
}
}
Once you have that working, you can add other elements to the view. Just make sure you have a "chain" of vertical spacing constraints, with the top-most element constrained to the top of the green superview, and the bottom-most element constrained to the bottom of the green superview.