Handle negative time spans

Question

Isn't there a TimeSpan.Duration method? I think this would handle what you are trying to do.

Returns a new TimeSpan object whose value is the absolute value of the current TimeSpan object.

static string ToHMString(TimeSpan timespan) { 
    if (timespan.Ticks < 0) return "-" + ToHMString(timespan.Negate());

    return timespan.TotalHours.ToString("#0") + ":" + timespan.Minutes.ToString("00");
}

Console.WriteLine(ToHMString(TimeSpan.FromHours(3)));       //Prints "3:00"
Console.WriteLine(ToHMString(TimeSpan.FromHours(-27.75)));  //Prints "-28:45"

This will also work correctly if the timespan is longer than 24 hours.

Just multiply it by -1 or use an absolute value function.

There is a Negate method in the TimeSpan class.

Link to the MSDN documentation: TimeSpan.Negate Method()

The simple solution would be to do:

string format = "HH:mm";
if(hours < 0)
  format = "-" + format;

hours = Math.Abs(hours)