Swift Playground 中使用SwiftUI

import UIKit
import SwiftUI
import PlaygroundSupport

private let dateFormatter: DateFormatter = {
    let dateFormatter = DateFormatter()
    dateFormatter.dateStyle = .medium
    dateFormatter.timeStyle = .medium
    return dateFormatter
}()

struct ContentView: View {
    @State private var dates = [Date]()
    
    var body: some View {
        NavigationView {
            MasterView(dates: $dates)
                .navigationBarTitle(Text("Master"))
                .navigationBarItems(
                    leading: EditButton(),
                    trailing: Button(
                        action: {
                            withAnimation { self.dates.insert(Date(), at: 0) }
                    }
                    ) {
                        Image(systemName: "plus")
                    }
            )
            DetailView()
        }.navigationViewStyle(DoubleColumnNavigationViewStyle())
    }
}

struct MasterView: View {
    @Binding var dates: [Date]
    
    var body: some View {
        List {
            ForEach(dates, id: \.self) { date in
                NavigationLink(
                    destination: DetailView(selectedDate: date)
                ) {
                    Text("\(date, formatter: dateFormatter)")
                }
            }.onDelete { indices in
                indices.forEach { self.dates.remove(at: $0) }
            }
        }
    }
}

struct DetailView: View {
    var selectedDate: Date?
    
    var body: some View {
        Group {
            if selectedDate != nil {
                Text("\(selectedDate!, formatter: dateFormatter)")
            } else {
                Text("Detail view content goes here")
            }
        }.navigationBarTitle(Text("Detail"))
    }
}


struct ContentView_Previews: PreviewProvider {
    static var previews: some View {
        ContentView()
    }
}

let contentView = ContentView()

PlaygroundPage.current.liveView = UIHostingController(rootView: contentView)