如何创建仅当使用SwiftUI打开应用程序时才显示的警报？

import SwiftUI

struct ContentView: View {
    @State private var showAlert = false
    
    var body: some View {
        Button(action: {
            showAlert = true
        }) {
            Text("显示警报")
        }
        .alert(isPresented: $showAlert) {
            Alert(title: Text("警报"), message: Text("这是一个示例警报"), dismissButton: .default(Text("确定")))
        }
    }
}

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