DateTime.Now作为参数值C＃

Question

I have a method that has a parameter of type DateTime that must not be in the past, which indicates when some other stuff executes. So naturally I want to use this method and pass DateTime.Now to it, so that everything happens as soon as possible.

The problem here is that DateTime.Now at the time of the call and DateTime.Now at the time it is actually checked will probably be different values, so how do I make sure that the date is not in the past, yet allow the method to be called with something like DateTime.Now? I don't want to add magic numbers here, but a general solution.

UPDATE. I've found this question How frequent is DateTime.Now updated

Answer 1

It seems to me that you have two options:

1. Add an appropriate small amount of time on to now (1 second say) so that you'll trigger things almost immediately. This will work, but its not nice.

2. Add another method (overload) that doesn't take a time parameter but instead actions immediately eg

   DoAction(attime); - will do the action at the stated time

   DoAction(); - will do the action now

The latter is a nicer solution but obviously there may be issues with how/where the method is available for use (and assumes you can add the method anyway).

Answer 2

If you want everything to happen as soon as possible why don't you rewrite your method to run as soon as it's called, or create an overload without the DateTime parameter to run as soon as it's called.

Using the overload of course would allow you to run your code at a time in the future (using the DateTime overload) or immediately.

Answer 3

这是一个哲学问题 - DateTime.Now总是在过去。

Answer 4

Compare the parameter on entry to DateTime.Now. If it's in the past, then use DateTime.Now.

Alternately, don't use a parameter; just use DateTime.Now.

Answer 5

如果时间足够接近，测试时必须有一定的容差。

Answer 6

Let your function take a Nullable<DateTime> . Interpret a null time to mean "do this immediately".

Answer 7

If you check that the passed DateTime parameter is equal to or greater than DateTime.Now at the beginning of the function, it is extremely unlikely that the system time would have changed between the time the function was called with DateTime.now and when the check is made. The system time is only updated every 10 or 15 milliseconds, and the actual function call time is much less than that.

To be sure that this never happens, however, you would have to check the passed time against DateTime.Now.Subtract(new TimeSpan(0, 0, 0, 0, 25)) , which would give the slight possibility of a time a little bit in the past being accepted.

Answer 8

Throw an ArgumentException if your date arg is in the past? This seems the simplest.

Answer 9

For the parameter, use a delegate returning a DateTime value. When calling the function, pass in a delegate pointing to a function that returns DateTime.Now .