timer - 设置一个重复的 24:00:00 倒计时计时器，该计时器在 00:00:00 停止并重置

Question

现在我得到一个倒数计时器，它实际上具有“24:00:00”的形式。问题是计时器在“00:00:00”后继续运行并开始倒数负数。我想要的是计时器停止在 0 并在 24 小时重复。我的问题是时间是 Data.type Date()。所以我不知道如何用 if 语句解释如果倒数计时器 == 0 时 textlabel 应该改变。我希望你理解这个问题

struct ContentView: View {

  // Timer

 func countDownString(from referenceDate: Date, until nowDate: Date) -> String
 {
     let components = calender.dateComponents([.hour, .minute, .second], from: nowDate, to: referenceDate)

     return String(format: "%02dh:%02dm:%02ds",
                   components.hour ?? 00,
                   components.minute ?? 00,
                   components.second ?? 00)


 }


@State var nowDate: Date = Date()
let referenceDate: Date = Date().addingTimeInterval(20)
let calender = Calendar(identifier: .gregorian)
let formatter = DateFormatter()


var timer: Timer {
   Timer.scheduledTimer(withTimeInterval: 1.0, repeats: true) {_ in
       self.nowDate = Date()

   }


 }


 var body: some View {

 Text(countDownString(from: referenceDate, until: nowDate)).font(.largeTitle).onAppear(perform: {
                    _ = self.timer

                })
}
}

标签： timerswiftui