Why isn't my TimeSpan.Add() working?

There has to be an easy answer:

var totalTime = TimeSpan.Zero;

foreach (var timesheet in timeSheets)
{
   //assume "time" is a correct, positive TimeSpan
   var time = timesheet.EndTime - timesheet.开发者_运维知识库StartTime;
   totalTime.Add(time);
}

There's only one value in the list timeSheets and it is a positive TimeSpan (verified on local inspection).

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TimeSpans are value types. Try:

totalTime = totalTime.Add(time)

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This is a common mistake. TimeSpan.Add returns a new instance of TimeSpan.

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totalTime = totalTime.Add(time)

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TimeSpans are value types and can use the += operator similar to integral and floating point numeric types. I find the += operator neat to use in this situation which is the same as writing x = x + y.

var totalTime = TimeSpan.Zero;

foreach (var timesheet in timeSheets)
{
   totalTime += (timesheet.EndTime - timesheet.StartTime);
}