Start a stopwatch from specified time

Question

Im trying to start a stopwatch from a given time (decimal value pulled from a database). However, because the Stopwatch.Elapsed.Add returns a new timespan rather than modify the stopwatch, I can't work out the best way forward.

var offsetTimeStamp = new System.TimeSpan(0,0,0).Add(TimeSpan.FromSeconds((double)jd.ActualTime));
Stopwatch.Elapsed.Add(offsetTimeStamp);
Stopwatch.Start();

Any ideas how I can do this? Cheers

Answer 1

The normal StopWatch does not support initialization with an offset timespan and TimeSpan is a struct, therefore Elapsed is immutable. You could write a wrapper around StopWatch:

public class StopWatchWithOffset
{
    private Stopwatch _stopwatch = null;
    TimeSpan _offsetTimeSpan;

    public StopWatchWithOffset(TimeSpan offsetElapsedTimeSpan)
    {
        _offsetTimeSpan = offsetElapsedTimeSpan;
        _stopwatch = new Stopwatch();
    }

    public void Start()
    {
        _stopwatch.Start();
    }

    public void Stop()
    {
        _stopwatch.Stop();
    }

    public TimeSpan ElapsedTimeSpan
    {
        get
        {
            return _stopwatch.Elapsed + _offsetTimeSpan;
        }
        set
        {
            _offsetTimeSpan = value;
        }
    }
}

Now you can add a start-timespan:

var offsetTimeStamp = TimeSpan.FromHours(1);
var watch = new StopWatchWithOffset(offsetTimeStamp);
watch.Start();
System.Threading.Thread.Sleep(300); 
Console.WriteLine(watch.ElapsedTimeSpan);// 01:00:00.2995983

Answer 2

The Elapsed property of StopWatch is read only, which makes sense. A stopwatch simply measures the amount of time that passed between start and stop.

If you want to add a timespan to the value - get the Elapsed value in a variable and add a timespan to it, after you have measured it (i.e. after stopping).

Answer 3

I think you want to start your Stopwatch after a certain mount of time specified by a TimeSpan. I wonder why you don't want to start your Stopwatch at a time specified by a DateTime instead?

public class MyStopwatch : Stopwatch
{
    public void Start(long afterMiliseconds)
    {
        Timer t = new Timer() { Interval = 1 };
        int i = 0;
        t.Tick += (s, e) =>
        {
            if (i++ == afterMiliseconds)
            {
                Start();
                t.Stop();
            }
        };
        t.Start();
    }
}
//use it
var offsetTimeStamp = new System.TimeSpan(0,0,0).Add(TimeSpan.FromSeconds((double)jd.ActualTime));
myStopwatch.Start((long)offsetTimeStamp.TotalMiliseconds);

Answer 4

If you locate this file into your project -- there is nothing you need to change in your project -- this wrapper have the same name, all of same methods/parameters as original stopwatch. But with additional few:

• additional SetOffset() method
• additional initialization with offset;

.

using System;

public class Stopwatch : System.Diagnostics.Stopwatch
{
    TimeSpan _offset = new TimeSpan();

    public Stopwatch()
    {
    }

    public Stopwatch(TimeSpan offset)
    {
        _offset = offset;
    }

    public void SetOffset(TimeSpan offsetElapsedTimeSpan)
    {
        _offset = offsetElapsedTimeSpan;
    }

    public TimeSpan Elapsed
    {
        get{ return base.Elapsed + _offset; }
        set{ _offset = value; }
    }

    public long ElapsedMilliseconds
    {
        get { return base.ElapsedMilliseconds + _offset.Milliseconds; }
    }

    public long ElapsedTicks
    {
        get { return base.ElapsedTicks + _offset.Ticks; }
    }

}