How to use the .NET Timer class to trigger an event at a specific time?

Question

I would like to have an event triggered in my app which runs continuously during the day at a certain time, say at 4:00pm. I thought about running the timer every second and when the time is equal to 4:00pm run the event. That works. But I'm wondering if there's a way to just get the callback once at 4:00pm and not having to keep checking.

Answer 1

How about something like this, using the System.Threading.Timer class?

var t = new Timer(TimerCallback);  // Figure how much time until 4:00 DateTime now = DateTime.Now; DateTime fourOClock = DateTime.Today.AddHours(16.0);  // If it's already past 4:00, wait until 4:00 tomorrow     if (now > fourOClock) {     fourOClock = fourOClock.AddDays(1.0); }  int msUntilFour = (int)((fourOClock - now).TotalMilliseconds);  // Set the timer to elapse only once, at 4:00. t.Change(msUntilFour, Timeout.Infinite); 

Note that if you use a System.Threading.Timer, the callback specified by TimerCallback will be executed on a thread pool (non-UI) thread—so if you're planning on doing something with your UI at 4:00, you'll have to marshal the code appropriately (e.g., using Control.Invoke in a Windows Forms app, or Dispatcher.Invoke in a WPF app).

Answer 2

Starting with .NET 4.5 there's a really clean solution:

public async void ScheduleAction(Action action, DateTime ExecutionTime) {     await Task.Delay((int)ExecutionTime.Subtract(DateTime.Now).TotalMilliseconds);     action(); } 

Here's a solution without async/await:

public void Execute(Action action, DateTime ExecutionTime) {     Task WaitTask = Task.Delay((int)ExecutionTime.Subtract(DateTime.Now).TotalMilliseconds);     WaitTask.ContinueWith(_ => action);     WaitTask.Start(); } 

It should be noted that this only works for about 24 days out because of int32 max value, which is plenty for your case, but worth noting.