Avoid undocked keyboard at bottom.

KeyboardAvoidingView.swift

// Sample code made in response to this tweet:
// https://twitter.com/stroughtonsmith/status/1485719749673820163

final class MainView: UIView {
    private let textView: UITextView = {
        let this = UITextView()
        this.translatesAutoresizingMaskIntoConstraints = false
        this.text = "I'm a text view"
        this.font = .preferredFont(forTextStyle: .body)
        this.textColor = .label
        return this
    }()
    private let leadingView: UIView = {
        let this = UIView()
        this.translatesAutoresizingMaskIntoConstraints = false
        this.backgroundColor = .systemBlue
        this.isUserInteractionEnabled = false
        return this
    }()
    private let trailingView: UIView = {
        let this = UIView()
        this.translatesAutoresizingMaskIntoConstraints = false
        this.backgroundColor = .systemBlue
        this.isUserInteractionEnabled = false
        return this
    }()

    init() {
        super.init(frame: .zero)
        setupView()
        setupLayout()
    }

    required init?(coder aDecoder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }

    private func setupView() {
        backgroundColor = .systemBackground
        keyboardLayoutGuide.followsUndockedKeyboard = true
        addSubview(textView)
        addSubview(leadingView)
        addSubview(trailingView)
    }

    private func setupLayout() {
        let leadingViewBottomConstraint = leadingView.bottomAnchor.constraint(equalTo: layoutMarginsGuide.bottomAnchor)
        let trailingViewBottomConstraint = trailingView.bottomAnchor.constraint(equalTo: layoutMarginsGuide.bottomAnchor)
        leadingViewBottomConstraint.priority = .defaultHigh
        trailingViewBottomConstraint.priority = .defaultHigh
        NSLayoutConstraint.activate([
            textView.leadingAnchor.constraint(equalTo: layoutMarginsGuide.leadingAnchor),
            textView.trailingAnchor.constraint(equalTo: trailingAnchor),
            textView.topAnchor.constraint(equalTo: topAnchor),
            textView.bottomAnchor.constraint(equalTo: bottomAnchor),

            leadingView.leadingAnchor.constraint(equalTo: layoutMarginsGuide.leadingAnchor),
            leadingViewBottomConstraint,
            leadingView.widthAnchor.constraint(equalToConstant: 300),
            leadingView.heightAnchor.constraint(equalToConstant: 170),

            trailingView.trailingAnchor.constraint(equalTo: layoutMarginsGuide.trailingAnchor),
            trailingViewBottomConstraint,
            trailingView.widthAnchor.constraint(equalToConstant: 300),
            trailingView.heightAnchor.constraint(equalToConstant: 170)
        ])

        keyboardLayoutGuide.setConstraints([
            leadingView.bottomAnchor.constraint(equalTo: keyboardLayoutGuide.topAnchor, constant: -15)
        ], activeWhenNearEdge: [.bottom, .leading])

        keyboardLayoutGuide.setConstraints([
            trailingView.bottomAnchor.constraint(equalTo: keyboardLayoutGuide.topAnchor, constant: -15)
        ], activeWhenNearEdge: [.bottom, .trailing])
    }
}