NSLayoutConstraint - Two items, one line, spacing priority

Question

I have two labels on one line. I need the second label to be right up against the end of the first label, but I need to make sure the second label never runs past the edge of the screen.

So I have label1's left anchor aligned to the left of the container view, and I have label2's left anchor constrained to the right of label1, and the right anchor of label2 constrained to the right of the container.

I want label1 to take up only as much space as it needs, and label2 to take up the rest of the space. What I have is exactly the opposite.

So I need the exact opposite of what I have here. How can I do that?

Answer 1

Giving the left label a higher content hugging priority should do the trick.

// In code
leftLabel.setContentHuggingPriority(.defaultHigh, for: .horizontal)

For further reading on that topic, I found this to be pretty helpful

Playground example

//: A UIKit based Playground for presenting user interface
  
import UIKit
import PlaygroundSupport

class MyViewController : UIViewController {
    
    override func loadView() {
        let view = UIView()
        view.backgroundColor = .white

        let leftLabel = UILabel()
        leftLabel.text = "I am left"
        leftLabel.backgroundColor = .orange
        leftLabel.translatesAutoresizingMaskIntoConstraints = false
        
        let rightLabel = UILabel()
        rightLabel.text = "I am right"
        rightLabel.backgroundColor = .yellow
        rightLabel.translatesAutoresizingMaskIntoConstraints = false
        
        view.addSubview(leftLabel)
        view.addSubview(rightLabel)
        
        leftLabel.leadingAnchor.constraint(equalTo: view.leadingAnchor, constant: 16).isActive = true
        leftLabel.trailingAnchor.constraint(equalTo: rightLabel.leadingAnchor).isActive = true
        leftLabel.topAnchor.constraint(equalTo: view.topAnchor, constant: 16).isActive = true
        
        // This is the important part
        leftLabel.setContentHuggingPriority(.defaultHigh, for: .horizontal)
        
        rightLabel.trailingAnchor.constraint(equalTo: view.trailingAnchor, constant: -16).isActive = true
        rightLabel.topAnchor.constraint(equalTo: leftLabel.topAnchor).isActive = true
        
        self.view = view
    }
}
// Present the view controller in the Live View window
PlaygroundPage.current.liveView = MyViewController()