TimerSwiftUI.swift

import SwiftUI

struct GameDetail: View {
  @State var nowDate = Date()

  private var refDate: Date {
    let formatter = DateFormatter()
    formatter.dateFormat = "YYYY-MM-dd HH:mm:ss"
    let rDate = formatter.date(from: "20019-10-11 12:12:12")
    return rDate!
  }

  private var timer: Timer {
    return Timer.scheduledTimer(withTimeInterval: 1, repeats: true) { _ in
      self.nowDate = Date()
    }
  }

  var body: some View {
    VStack {
      Image(uiImage: UIImage(named: "gameImage")!)
        .resizable()
        .aspectRatio(contentMode: .fit)
        .cornerRadius(10.0)
      Text("\(nowDate.distance(to: refDate).description) Until game release")
    }
      .onAppear {
        _ = self.timer
    }
  }
}

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