ViewController.swift

//
//  ViewController.swift
//  AutolayoutTest
//
//  Created by Zhiyuan Sun on 3/19/21.
//

import UIKit

class MyView: UIView {
    private lazy var label: UILabel = {
        let label = UILabel()
        label.translatesAutoresizingMaskIntoConstraints = false
        label.text = "This is a label that might have dynamic length,This is a label that might have dynamic lengthThis is a label that might have dynamic length"
        label.numberOfLines = 0
        label.textAlignment = .center
        return label
    }()
    
    init() {
        super.init(frame: .zero)
        backgroundColor = .gray
        translatesAutoresizingMaskIntoConstraints = false
        addSubview(label)
        NSLayoutConstraint.activate([
            label.topAnchor.constraint(equalTo: topAnchor, constant: 20),
            label.bottomAnchor.constraint(equalTo: bottomAnchor, constant: -20),
            label.leadingAnchor.constraint(equalTo: leadingAnchor, constant: 80),
            label.trailingAnchor.constraint(equalTo: trailingAnchor, constant: -80),
        ])
    }
    
    required init?(coder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }
}

class ViewController: UIViewController {
    
    private lazy var footer = MyView()
    private lazy var header = MyView()
    private lazy var middle = MyView()

    override func viewDidLoad() {
        super.viewDidLoad()
        view.backgroundColor = .red
        
        view.addSubview(footer)
        view.addSubview(header)
        NSLayoutConstraint.activate([
            footer.bottomAnchor.constraint(equalTo: view.bottomAnchor),
            footer.leadingAnchor.constraint(equalTo: view.leadingAnchor),
            footer.trailingAnchor.constraint(equalTo: view.trailingAnchor),
            header.topAnchor.constraint(equalTo: view.topAnchor),
            header.leadingAnchor.constraint(equalTo: view.leadingAnchor),
            header.trailingAnchor.constraint(equalTo: view.trailingAnchor),
        ])
        

//        view.addSubview(middle)
//        NSLayoutConstraint.activate([
//            middle.topAnchor.constraint(equalTo: header.bottomAnchor, constant: 20),
//            middle.bottomAnchor.constraint(equalTo: footer.topAnchor, constant: -20),
//            middle.leadingAnchor.constraint(equalTo: view.leadingAnchor, constant: 20),
//            middle.trailingAnchor.constraint(equalTo: view.trailingAnchor, constant: -20),
//        ])
    }
}