System.Timers.Timer How to get the time remaining until Elapse

Question

Using C#, how may I get the time remaining (before the elapse event will occur) from a System.Timers.Timer object?

In other words, let say I set the timer interval to 6 hours, but 3 hours later, I want to know how much time is remaining. How would I get the timer object to reveal this time remaining?

Portugal

Answer 1

The built-in timer doesn't provide the time remaining until elapse. You'll need to create your own class which wraps a timer and exposes this info.

Something like this should work.

public class TimerPlus : IDisposable
{
    private readonly TimerCallback _realCallback;
    private readonly Timer _timer;
    private TimeSpan _period;
    private DateTime _next;

    public TimerPlus(TimerCallback callback, object state, TimeSpan dueTime, TimeSpan period)
    {
        _timer = new Timer(Callback, state, dueTime, period);
        _realCallback = callback;
        _period = period;
        _next = DateTime.Now.Add(dueTime);
    }

    private void Callback(object state)
    {
        _next = DateTime.Now.Add(_period);
        _realCallback(state);
    }

    public TimeSpan Period => _period;
    public DateTime Next => _next;
    public TimeSpan DueTime => _next - DateTime.Now;

    public bool Change(TimeSpan dueTime, TimeSpan period)
    {
        _period = period;
        _next = DateTime.Now.Add(dueTime);
        return _timer.Change(dueTime, period);
    }

    public void Dispose() => _timer.Dispose();
}

Residuary

Above and beyond the call, but checked you for your efforts. Thanks, you are very kind. I already have a method that will calculate how much time should be remaining, but wanted to confirm it with output from the actual timer object itself. To bad it isn't inherently provided. – Portugal

Yeah, he wrote that fast too. Impressive. – Portugal

Samuel, could you provide the usage of this class? I am unsure how to pass in the parameters to your constructor. – Semite

@HeseinBurg TimerPlus is a drop-in replacement for Timer (meaning you can use TimerPlus as-is wherever you use Timer). It has the same functionality and API. The addition is the Next property which will always return the DateTime that it will next be triggered. – Residuary

Wouldn't this result in a bug in case the user would change the system time while the timer is running? – Portent

@Portent Yes. The timer will not actually fire at the wrong time but Next and DueTime will both be wrong until the next timer tick. – Residuary

Answer 2

I am aware, that the topic is more than 3 years old. However I came across it while tackling exactly the same problem.

Inspired by Samuel Neff, I came up with a WinForms-less solution by extending the standard System.Timers.Timer class:

public class TimerPlus : System.Timers.Timer
{
    private DateTime m_dueTime;

    public TimerPlus() : base() => this.Elapsed += this.ElapsedAction;

    protected new void Dispose()
    {
        this.Elapsed -= this.ElapsedAction;
        base.Dispose();
    }

    public double TimeLeft => (this.m_dueTime - DateTime.Now).TotalMilliseconds;
    public new void Start()
    {
        this.m_dueTime = DateTime.Now.AddMilliseconds(this.Interval);
        base.Start();
    }

    private void ElapsedAction(object sender, System.Timers.ElapsedEventArgs e)
    {
        if (this.AutoReset)
            this.m_dueTime = DateTime.Now.AddMilliseconds(this.Interval);
    }
}

I hope it helps.

Logos

Answer 3

I guess the best method is to hold the start time in a variable and then calculate the elapsed time as

TimeSpan t = DateTime.Now - StartTime;

Pavia

I agree. But, had to check Sam for his efforts; he wrote a class to help me. Super kind. Thank you both. – Portugal