How do you compare DateTime objects using a specified tolerance in C#?
I usally use the TimeSpan.FromXXX methods to do something like this:
if((myDate - myOtherDate) > TimeSpan.FromSeconds(10))
{
//Do something here
}
if (Math.Abs(dt1.Subtract(dt2).TotalSeconds) < 1.0)
How about an extension method for DateTime to make a bit of a fluent interface (those are all the rage right?)
public static class DateTimeTolerance
{
private static TimeSpan _defaultTolerance = TimeSpan.FromSeconds(10);
public static void SetDefault(TimeSpan tolerance)
{
_defaultTolerance = tolerance;
}
public static DateTimeWithin Within(this DateTime dateTime, TimeSpan tolerance)
{
return new DateTimeWithin(dateTime, tolerance);
}
public static DateTimeWithin Within(this DateTime dateTime)
{
return new DateTimeWithin(dateTime, _defaultTolerance);
}
}
This relies on a class to store the state and define a couple operator overloads for == and != :
public class DateTimeWithin
{
public DateTimeWithin(DateTime dateTime, TimeSpan tolerance)
{
DateTime = dateTime;
Tolerance = tolerance;
}
public TimeSpan Tolerance { get; private set; }
public DateTime DateTime { get; private set; }
public static bool operator ==(DateTime lhs, DateTimeWithin rhs)
{
return (lhs - rhs.DateTime).Duration() <= rhs.Tolerance;
}
public static bool operator !=(DateTime lhs, DateTimeWithin rhs)
{
return (lhs - rhs.DateTime).Duration() > rhs.Tolerance;
}
public static bool operator ==(DateTimeWithin lhs, DateTime rhs)
{
return rhs == lhs;
}
public static bool operator !=(DateTimeWithin lhs, DateTime rhs)
{
return rhs != lhs;
}
}
Then in your code you can do:
DateTime d1 = DateTime.Now;
DateTime d2 = d1 + TimeSpan.FromSeconds(20);
if(d1 == d2.Within(TimeSpan.FromMinutes(1))) {
// TRUE! Do whatever
}
The extension class also houses a default static tolerance so that you can set a tolerance for your whole project and use the Within method with no parameters:
DateTimeTolerance.SetDefault(TimeSpan.FromMinutes(1));
if(d1 == d2.Within()) { // Uses default tolerance
// TRUE! Do whatever
}
I have a few unit tests but that'd be a bit too much code for pasting here.
You need to remove the milliseconds component from the date object. One way is:
DateTime d = DateTime.Now;
d.Subtract(new TimeSpan(0, 0, 0, 0, d.Millisecond));
You can also subtract two datetimes
d.Subtract(DateTime.Now);
This will return a timespan object which you can use to compare the days, hours, minutes and seconds components to see the difference.