【Swift】オートレイアウトの位置、サイズなどの制約をコードのみで設定する方法を徹底解説！

import UIKit

class ViewController: UIViewController {
    override func viewDidLoad() {
        super.viewDidLoad()
        
        let subView = UIView()
        subView.backgroundColor = .red
        subView.translatesAutoresizingMaskIntoConstraints = false
        view.addSubview(subView)
        
        // 中央に配置する制約
        NSLayoutConstraint.activate([
            subView.centerXAnchor.constraint(equalTo: view.centerXAnchor),
            subView.centerYAnchor.constraint(equalTo: view.centerYAnchor),
            subView.widthAnchor.constraint(equalToConstant: 100),
            subView.heightAnchor.constraint(equalToConstant: 100)
        ])
    }
}

childView.topAnchor.constraint(equalTo: parentView.topAnchor, constant: padding).isActive = true

childView.bottomAnchor.constraint(equalTo: parentView.bottomAnchor, constant: -padding).isActive = true

childView.leadingAnchor.constraint(equalTo: parentView.leadingAnchor, constant: padding).isActive = true

childView.trailingAnchor.constraint(equalTo: parentView.trailingAnchor, constant: -padding).isActive = true

import UIKit

class ViewController: UIViewController {
    override func viewDidLoad() {
        super.viewDidLoad()
        
        let subView = UIView()
        subView.backgroundColor = .green
        subView.translatesAutoresizingMaskIntoConstraints = false
        view.addSubview(subView)
        
        // 幅を親ビューの半分に設定
        NSLayoutConstraint.activate([
            subView.widthAnchor.constraint(equalTo: view.widthAnchor, multiplier: 0.5),
            subView.heightAnchor.constraint(equalToConstant: 100),
            subView.centerXAnchor.constraint(equalTo: view.centerXAnchor),
            subView.centerYAnchor.constraint(equalTo: view.centerYAnchor)
        ])
    }
}

// 幅を200ポイントに設定
let widthConstraint = myView.widthAnchor.constraint(equalToConstant: 200)
widthConstraint.isActive = true

// 高さを100ポイントに設定
let heightConstraint = myView.heightAnchor.constraint(equalToConstant: 100)
heightConstraint.isActive = true

// 幅を親ビューの50%に設定
let widthConstraint = myView.widthAnchor.constraint(equalTo: view.widthAnchor, multiplier: 0.5)
widthConstraint.isActive = true

// 幅に基づいてアスペクト比を16:9に設定
let aspectRatioConstraint = myView.widthAnchor.constraint(equalTo: myView.heightAnchor, multiplier: 16.0/9.0)
aspectRatioConstraint.isActive = true