как использовать UITraitCollection в swift?

Question

нужно изменить constraints в зависимости от положения телефона с использованием UITaitCollection, как это сделать?


class ViewController: UIViewController {
    
    var redView: UIView!
    var blueView: UIView!
    
    override func loadView() {
        view = UIView()
        view.backgroundColor = .white
        
        redView = UIView()
        redView.translatesAutoresizingMaskIntoConstraints = false
        redView.backgroundColor = .red
        view.addSubview(redView)
        
        blueView = UIView()
        blueView.translatesAutoresizingMaskIntoConstraints = false
        blueView.backgroundColor = .blue
        view.addSubview(blueView)

        
        NSLayoutConstraint.activate([
            
            redView.topAnchor.constraint(equalTo: view.layoutMarginsGuide.topAnchor, constant: 16),
            redView.leadingAnchor.constraint(equalTo: view.layoutMarginsGuide.leadingAnchor, constant: 16),
            redView.trailingAnchor.constraint(equalTo: view.layoutMarginsGuide.trailingAnchor, constant: -16),
            redView.heightAnchor.constraint(equalTo: view.layoutMarginsGuide.heightAnchor, multiplier: 0.5),
            
            
            blueView.topAnchor.constraint(equalTo: redView.bottomAnchor, constant: 16),
            blueView.trailingAnchor.constraint(equalTo: view.layoutMarginsGuide.trailingAnchor, constant: -16),
            blueView.leadingAnchor.constraint(equalTo: view.layoutMarginsGuide.leadingAnchor, constant: 16),
            blueView.bottomAnchor.constraint(equalTo: view.layoutMarginsGuide.bottomAnchor, constant: 16),
            blueView.heightAnchor.constraint(equalTo: view.layoutMarginsGuide.heightAnchor, multiplier: 0.5, constant: -16),
            
            
        ])
        
        
    }
    
}

это очень неудачная попытка

 func traitCollectionDidChange(_ previousTraitCollection: UITraitCollection?) {

        redView = UIView()
        redView.translatesAutoresizingMaskIntoConstraints = false
        redView.backgroundColor = .red
        view.addSubview(redView)
        
        blueView = UIView()
        blueView.translatesAutoresizingMaskIntoConstraints = false
        blueView.backgroundColor = .blue
        view.addSubview(blueView)

    if traitCollection.horizontalSizeClass == .compact {
        
NSLayoutConstraint.activate([
            
            redView.topAnchor.constraint(equalTo: view.layoutMarginsGuide.topAnchor, constant: 16),
            redView.leadingAnchor.constraint(equalTo: view.layoutMarginsGuide.leadingAnchor, constant: 16),
            redView.trailingAnchor.constraint(equalTo: view.layoutMarginsGuide.trailingAnchor, constant: -16),
            redView.heightAnchor.constraint(equalTo: view.layoutMarginsGuide.heightAnchor, multiplier: 0.5),
            
            
            blueView.topAnchor.constraint(equalTo: redView.bottomAnchor, constant: 16),
            blueView.trailingAnchor.constraint(equalTo: view.layoutMarginsGuide.trailingAnchor, constant: -16),
            blueView.leadingAnchor.constraint(equalTo: view.layoutMarginsGuide.leadingAnchor, constant: 16),
            blueView.bottomAnchor.constraint(equalTo: view.layoutMarginsGuide.bottomAnchor, constant: 16),
            blueView.heightAnchor.constraint(equalTo: view.layoutMarginsGuide.heightAnchor, multiplier: 0.5, constant: -16),
            
            
        ])

    } else {
        
    }
}

Answer 1

Констрейнты в ViewController уже реагируют на поворот экрана, попробуйте вот так:

import UIKit

class ViewController: UIViewController {
    
    var redView: UIView!
    var blueView: UIView!
    
    override func loadView() {
        view = UIView()
        view.backgroundColor = .white
        
        redView = UIView()
        redView.translatesAutoresizingMaskIntoConstraints = false
        redView.backgroundColor = .red
        view.addSubview(redView)
        
        blueView = UIView()
        blueView.translatesAutoresizingMaskIntoConstraints = false
        blueView.backgroundColor = .blue
        view.addSubview(blueView)
        
        NSLayoutConstraint.activate([
            redView.topAnchor.constraint(equalTo: view.layoutMarginsGuide.topAnchor, constant: 16),
            redView.leadingAnchor.constraint(equalTo: view.layoutMarginsGuide.leadingAnchor, constant: 16),
            redView.trailingAnchor.constraint(equalTo: view.layoutMarginsGuide.trailingAnchor, constant: -16),
            redView.heightAnchor.constraint(equalTo: blueView.heightAnchor),
                        
            blueView.topAnchor.constraint(equalTo: redView.bottomAnchor, constant: 16),
            blueView.leadingAnchor.constraint(equalTo: view.layoutMarginsGuide.leadingAnchor, constant: 16),
            blueView.trailingAnchor.constraint(equalTo: view.layoutMarginsGuide.trailingAnchor, constant: -16),
            blueView.bottomAnchor.constraint(equalTo: view.layoutMarginsGuide.bottomAnchor, constant: -16),
        ])
    }
}

А вообще, вначале нужно деактивировать используемые констрейнты:

override func traitCollectionDidChange(_ previousTraitCollection: UITraitCollection?) {
    super.traitCollectionDidChange(previousTraitCollection)
    
    if traitCollection.horizontalSizeClass == .compact {
        NSLayoutConstraint.deactivate(...)
        NSLayoutConstraint.activate(...)
    } else {
        ...
    }
}

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как использовать UITraitCollection в swift?

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