Timer 计时器构造函数

Timer(
  1. Duration duration,
  2. void callback(
      )
    )

    创建一个新的计时器。

    在给定的 duration 之后调用 callback 函数。

    例子

    final timer =
    Timer(const Duration(seconds: 5), () => print('Timer finished'));
// Outputs after 5 seconds: "Timer finished".

    实现

    factory Timer(Duration duration, void Function() callback) {
  if (Zone.current == Zone.root) {
    // No need to bind the callback. We know that the root's timer will
    // be invoked in the root zone.
    return Zone.current.createTimer(duration, callback);
  }
  return Zone.current
      .createTimer(duration, Zone.current.bindCallbackGuarded(callback));
}