SwiftUI Keyboard Adapter

View+KeyboardAdapter.swift

import Combine
import SwiftUI
import UIKit

private struct KeyboardInfo {
    let height: CGFloat
    let eventuallyVisible: Bool

    private let animationDuration: Double

    var animation: Animation {
        .easeOut(duration: animationDuration)
    }

    var edgesIgnoringSafeArea: Edge.Set {
        eventuallyVisible ? [.bottom] : []
    }

    init() {
        self.eventuallyVisible = false
        self.height = 0
        self.animationDuration = 0
    }

    init?(notification: Notification) {
        guard let frame = notification.userInfo?[UIResponder.keyboardFrameEndUserInfoKey] as? CGRect,
            let duration = notification.userInfo?[UIResponder.keyboardAnimationDurationUserInfoKey] as? NSNumber else {
            return nil
        }

        switch notification.name {
        case UIResponder.keyboardWillShowNotification, UIResponder.keyboardWillChangeFrameNotification:
            self.eventuallyVisible = true
            self.height = frame.size.height
        default:
            self.eventuallyVisible = false
            self.height = 0
        }
        self.animationDuration = duration.doubleValue
    }
}

private final class Keyboard: ObservableObject {
    @Published var info = KeyboardInfo()

    private var subscription: AnyCancellable?

    func cancelKeyboardEventsSubscription() {
        subscription?.cancel()
        subscription = nil
    }

    func subscribeToKeyboardEvents() {
        guard subscription == nil else { return }

        subscription = Publishers.Sequence(sequence: [
            UIResponder.keyboardWillShowNotification,
            UIResponder.keyboardWillHideNotification,
            UIResponder.keyboardWillChangeFrameNotification,
        ])
            .map { NotificationCenter.default.publisher(for: $0) }
            .flatMap { Publishers.MergeMany($0) }
            .map { KeyboardInfo(notification: $0) }
            .compactMap { $0 }
            .receive(on: RunLoop.main)
            .assign(to: \.info, on: self)
    }
}

struct KeyboardAdapter: ViewModifier {
    @ObservedObject private var keyboard = Keyboard()

    func body(content: Content) -> some View {
        content
            .padding(.bottom, keyboard.info.height)
            .animation(keyboard.info.animation)
            .edgesIgnoringSafeArea(keyboard.info.edgesIgnoringSafeArea)
            .onAppear(perform: keyboard.subscribeToKeyboardEvents)
            .onDisappear(perform: keyboard.cancelKeyboardEventsSubscription)
    }
}

extension View {
    func adaptToKeyboard() -> some View {
        self.modifier(KeyboardAdapter())
    }
}