找不到类型“ databaseerference”在范围

Question

我正在使用Xcode 13，并且已经设置了将实时数据库与Swift UI应用程序连接的，我希望将数据写入Firebase，但是在此步骤中，我会遇到错误 Here is my to config firebase

import SwiftUI
import Firebase
@main
struct FirebaseDatabaseApp: App {
    init(){
        FirebaseApp.configure()
    }
    var body: some Scene {
        WindowGroup {
            ContentView()
        }
    }
}

And file contentview.swift

import SwiftUI
import Firebase
struct ContentView: View {
    var body: some View {
        var ref: DatabaseReference! //I have a err here
        Text("Hello, world!")
            .padding()
    }
}

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

I try to create new class on another file but it still not work 我如何实现将数据写入实时数据库的目标， 我正在关注Firebase文档