Question

我试图节省调用函数start的时间，但是在调用OneSignal.initWithLaunchOptions(launchOptions, appId: "YOUR ONE SIGNAL APP ID HERE", handleNotificationAction: { (result) in let payload = result?.notification.payload if let additionalData = payload?.additionalData { let destination = additionalData["destination"] as? String ?? "" print("the destination is: \(destination)") } },settings: onesignalInitSettings)之后，setStartTS()仍然为空。我不确定requestAnimationFrame是否在此处引入任何类型的错误，以及有关问题可能在何处的任何想法

startTS

Answer 1

React的钩子提供了一个名为useEffect的api。安装组件时，可能需要此函数来调用start()函数。

const Chrono = () => {
  const [startTS, setStartTS] = useState(null);
  const [diff, setDiff] = useState(null);
  const [intervalId, setIntervalId] = useState(null);

  // --> add effect
  useEffect(() => {
    start();
  });

  const start = () => {
    if (startTS) {
      return;
    }
    const tic = +new Date();
    setStartTS(tic);
    setIntervalId(requestAnimationFrame(tick));
  };

  const tick = () => {
    const tock = +new Date();
    const timePassed = tock - startTS;
    setDiff(timePassed);
    setIntervalId(requestAnimationFrame(tick));
  };

  return (...)
}

有关useEffect api的更多详细信息，请查看here

useState setter不更新其状态的值

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