swiftui_floating_button.swift

import SwiftUI
import Combine

class KeyboardService: ObservableObject {
    @Published var keyboardHeight: CGFloat = 0.0
    let defaultNotification = NotificationCenter.default

    func start() {
        defaultNotification.addObserver(
            self,
            selector: #selector(self.keyboardWillShow(_:)),
            name: UIResponder.keyboardWillShowNotification,
            object: nil)
        defaultNotification.addObserver(
            self,
            selector: #selector(self.keyboardWillHide(_:)),
            name: UIResponder.keyboardWillHideNotification,
            object: nil)
    }

    func end() {
        NotificationCenter
            .default
            .removeObserver(
                self,
                name: UIResponder.keyboardWillShowNotification,
                object: nil)
        NotificationCenter
            .default
            .removeObserver(
                self,
                name: UIResponder.keyboardWillHideNotification,
                object: nil)
    }

    @objc func keyboardWillShow(_ notification: Notification) {
        guard let rect = (notification
            .userInfo?[UIResponder.keyboardFrameEndUserInfoKey] as? NSValue)?.cgRectValue else { return }
        self.keyboardHeight = rect.size.height
    }

    @objc func keyboardWillHide(_ notification: Notification) {
        self.keyboardHeight = 0
    }
}

struct ContentView: View {
    var body: some View {
        InputView()
    }
}

struct InputView: View {
    @State var inputText = ""
    @State var outputText = ""
    @ObservedObject var keyboard = KeyboardService()

    var body: some View {
        ZStack {
            VStack {
                Text(outputText)
                TextField(
                    "入力してね",
                    text: $inputText,
                    onEditingChanged: { editing in
                }).padding()
            }
            FloatingButton(
                bottomPadding: self.keyboard.keyboardHeight,
                tappedHandler: self.showText,
                isDisabled: inputText.isEmpty
            )
        }.onAppear {
            self.keyboard.start()
        }.onDisappear {
            self.keyboard.end()
        }
    }

    func showText() {
        outputText = inputText
    }
}

struct FloatingButton: View {
    var bottomPadding: CGFloat = 0
    var tappedHandler: (() -> Void)? = nil
    var isDisabled: Bool = false
    var body: some View {
        VStack {
            Spacer()
            HStack {
                Spacer()
                Button(action: {
                    self.tappedHandler?()
                }, label: {
                    Image(systemName: "pencil")
                        .foregroundColor(.white)
                        .font(.system(size: 24))
                })
                    .frame(width: 60, height: 60)
                    .background(backgroundColor)
                    .cornerRadius(30.0)
                    .shadow(color: .gray, radius: 3, x: 3, y: 3)
                    .padding(EdgeInsets(top: 0, leading: 0, bottom: bottomPadding + 16.0, trailing: 16.0))
                    .animation(.easeOut)
                    .disabled(isDisabled)
            }
        }
    }

    var backgroundColor: Color {
        return isDisabled ? Color.gray : Color.orange
    }
}