ContentView.swift

import SwiftUI

struct ContentView: View {
    
    @State private var show = false
 
    var body: some View {
        NavigationView {
           List(["1", "2", "3", "4", "5"], id: \.self) { row in
               Text(row)
           }
           .navigationBarTitle(Text("With NavigationView"))
           .navigationBarItems(trailing: Button(action: {
                self.show.toggle()
           }) {
               Text("Show")
           })
        }
//        VStack {
//            Text("Without NavigationView")
//            Button(action: {
//                self.show.toggle()
//            }) {
//                Text("Show")
//            }
//            Spacer()
//        }
        .toast(show: $show, text: "Test")
    }
    
}

struct ToastView<Content>: View where Content: View {
    
    @Binding var show: Bool
    
    let text: String
    
    var overlaidContent: () -> Content
    
    var body: some View {
        GeometryReader { geometry in
            ZStack(alignment: .bottom) {
                self.overlaidContent()
                
                if self.show {
                    VStack {
                        Text(self.text)
                            .multilineTextAlignment(.center)
                            .padding()
                    }
                    .frame(width: geometry.size.width < geometry.size.height ? geometry.size.width * 0.85 : geometry.size.width * 0.65)
                    .background(Color(UIColor.secondarySystemBackground))
                    .cornerRadius(20)
                    .padding([.vertical], 15)
                    .animation(.easeInOut(duration: 1.0))
                    .transition(.move(edge: .bottom))
                    .onAppear {
                        DispatchQueue.main.asyncAfter(deadline: .now() + 3) {
                            self.show.toggle()
                        }
                    }
                }
            }
        }
    }
    
}

extension View {
    func toast(show: Binding<Bool>, text: String) -> some View {
        ToastView(show: show, text: text) {
            self
        }
    }
}

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