How to estimate end time of method in WinForms to properly inform user about predicted time of finish?

Question

I've got some timers that measure the time to execute code.

 DateTime startTimeFunctionTotal = DateTime.Now;
     for (int i = 0; i < array.Count; i++) {
         DateTime startTimeFunction = DateTime.Now;
         //some code here

          DateTime stopTimeFunction = DateTime.Now;
          TimeSpan durationTimeFunction = stopTimeFunction - startTimeFunction ;

 }
 DateTime stopTimeFunctionTotal = DateTime.Now;
 TimeSpan durationTimeFunctionTotal = stopTimeFunctionTotal - startTimeFunctionTotal ;

It's allowed (even better) if the predicted time changes according to more data (every loop there is more data so prediction should be more accurate).

I would like to give user a predicted time of finish (both time like 15 minutes, and 10:56).

Answer 1

Assuming each action in your for statement takes roughly the same amount of time:

List<TimeSpan> timeSpans = new List<TimeSpan>();
for(int i = 0; i < array.Count; i++)
{
    Stopwatch watch = Stopwatch.StartNew();
    //do stuff
    timeSpans.Add(watch.Elapsed);
    long ticksLeft = timeSpans.Sum(ts => ts.Ticks) * (array.Count - i) / timeSpans.Count;
    Console.WriteLine("Left: " + new TimeSpan(ticksLeft));
    Console.WriteLine("Finished in: " + 
        DateTime.Now.AddTicks(ticksLeft));
}

To go with the median use:

long ticksLeft = timeSpans.OrderBy(ts => ts.Ticks)
    .ElementAt(timeSpans.Count / 2).Ticks * (array.Count - i);