Simple Timer for Xamarin Forms using Device Timer

While developing your application in Xamarin that requires a Timer, you have the option to use the Device Timer. However, one of the first caveat your would notice is that while Device Class has a Device.StartTimer method, it does not exposes a Stop method, leaving it to your own class to handle it.

I started by writing an interface for my proposed Timer Class ( in my case a Countdown timer), so that I could use it for mocking for the sake of my Unit Tests. This is how my interface looked like.

public class TimerEventArgs:EventArgs
public TimeSpan TimeRemaining { get; set; }

public interface ICountdownTimer
void Start(TimeSpan CountdownTime);
void Stop();

event EventHandler<TimerEventArgs> Ticked;
event EventHandler Completed;
event EventHandler Aborted;
Following is how the implementation looked like.
public class CountdownTimer : ICountdownTimer
#region Private Variable
private bool _Stopped = false;
private TimeSpan _Second = new TimeSpan(0, 0, 1);

private readonly TimeSpan _Interval;
private TimeSpan _TimeRemaining;

private EventHandler _TickedEvent;
private EventHandler _CompletedEvent;
private EventHandler _AbortedEvent;

#region Ctor
public CountdownTimer()
_Interval = _Second;

#region ICountdownTimer

event EventHandler ICountdownTimer.Ticked
add { _TickedEvent += value; }
remove { _TickedEvent -= value;}

event EventHandler ICountdownTimer.Completed
add { _CompletedEvent += value; }
remove { _CompletedEvent -= value;}

event EventHandler ICountdownTimer.Aborted
add { _AbortedEvent += value; }
remove { _AbortedEvent -= value;}

public void Start(TimeSpan CountdownTime)
_TimeRemaining = CountdownTime;
_Stopped = false;

Device.StartTimer(_Interval, () =>
if (this._Stopped)
_AbortedEvent?.Invoke(this, EventArgs.Empty);
return false;

_TimeRemaining-= _Second;
_TickedEvent?.Invoke(this,new TimerEventArgs { TimeRemaining = _TimeRemaining });

_Stopped = _TimeRemaining.Duration() == TimeSpan.Zero;

if (_Stopped)
_CompletedEvent?.Invoke(this, EventArgs.Empty);

return !_Stopped;

public void Stop()
_Stopped = true;

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