SwifUI根据条件更新navigationBarItems标题

import SwiftUI

struct ContentView: View {
    @State private var navigationBarTitle = "默认标题"
    @State private var shouldShowAlternateTitle = false

    var body: some View {
        NavigationView {
            Text("这里是你的视图内容")
                .navigationBarTitle(navigationBarTitle)
                .navigationBarItems(trailing:
                    Button(action: {
                        self.shouldShowAlternateTitle.toggle()
                        self.navigationBarTitle = self.shouldShowAlternateTitle ? "备用标题" : "默认标题"
                    }) {
                        Text("切换标题")
                    }
                )
        }
    }
}

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