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• Behrooz Karjoo

我的应用程序需要做一个 事件触发 的功能，它需要每天定时执行，比如说当天的 16点，我现在的做法是使用一个 timer 按秒轮询判断当前是否为 16:00， 虽然可以玩得转，但我想能不能实现那种 16:00 自动触发回调函数的模式，而不是现在无时无刻的轮询。

回答区

• noontz

其实很简单，计算触发时间与当前时间的差值，然后将 差值 作为精确的延迟时间，带入到 Task.Delay 中即可，外面再套个 while(true) ，下面是我封装的代码。

/// <summary>
/// Utility class for triggering an event every 24 hours at a specified time of day
/// </summary>
public class DailyTrigger : IDisposable
{/// <summary>/// Time of day (from 00:00:00) to trigger/// </summary>TimeSpan TriggerHour { get; }/// <summary>/// Task cancellation token source to cancel delayed task on disposal/// </summary>CancellationTokenSource CancellationToken { get; set; }/// <summary>/// Reference to the running task/// </summary>Task RunningTask { get; set; }/// <summary>/// Initiator/// </summary>/// <param name="hour">The hour of the day to trigger</param>/// <param name="minute">The minute to trigger</param>/// <param name="second">The second to trigger</param>public DailyTrigger(int hour, int minute = 0, int second = 0){TriggerHour = new TimeSpan(hour, minute, second);CancellationToken = new CancellationTokenSource();RunningTask = Task.Run(async () => {while (true){var triggerTime = DateTime.Today + TriggerHour - DateTime.Now;if (triggerTime < TimeSpan.Zero)triggerTime = triggerTime.Add(new TimeSpan(24, 0, 0));await Task.Delay(triggerTime, CancellationToken.Token);OnTimeTriggered?.Invoke();}}, CancellationToken.Token);}/// <inheritdoc/>public void Dispose(){CancellationToken?.Cancel();CancellationToken?.Dispose();CancellationToken = null;RunningTask?.Dispose();RunningTask = null;}/// <summary>/// Triggers once every 24 hours on the specified time/// </summary>public event Action OnTimeTriggered;/// <summary>/// Finalized to ensure Dispose is called when out of scope/// </summary>~DailyTrigger() => Dispose();
}

然后像下面这样使用。

void Main()
{var trigger = new DailyTrigger(16); // every day at 4:00pmtrigger.OnTimeTriggered += () => {// Whatever};  Console.ReadKey();
}

点评区

思路是个好思路，不过在正式的项目开发中，建议还是用 Quartz.NET 或者 HangFire 这种专业的调度框架，毕竟它支持强大的 Cron 表达式。

RecurringJob.AddOrUpdate(() => MyMethod(), "* 16 * * *");