试图减去 DateTime “System.FormatException: String '12/9/2019 12:00:00 AM' 未被识别为有效的 DateTime。”

Question

So I'm trying to make a check for an Order . The difference between ArriveTime and OrderDate should be between 10 minutes and 2 hours. I formatted everything to what I think was correct, but I still get the error.

The values I put in ArriveTime is DateTime.Today and in OrderDate I put in DateTime.Now .

Code:

private bool TimerRequirements(IOrderData orderData)
{
     DateTime arriveTime = DateTime.ParseExact(orderData.ArriveTime.ToString(), "dd-MM-yyyy hh:mm:ss:tt", CultureInfo.InvariantCulture);
     DateTime orderDate = DateTime.ParseExact(orderData.OrderDate.ToString(), "dd-MM-yyyy hh:mm:ss:tt", CultureInfo.InvariantCulture);


     if (orderData.ArriveTime != null && Convert.ToDateTime(arriveTime.Subtract(orderDate)) >= orderData.OrderDate.AddMinutes(10) ||
            orderData.ArriveTime != null && Convert.ToDateTime(arriveTime.Subtract(orderDate)) <= orderData.OrderDate.AddHours(2))
     {
         return true;
     }
     else
     {
         return false;
     }
}

Answer 1

Dates have no format, they are binary values. The code causes the error by trying to convert the dates ti strings then back to dates. Just use

TimeSpan diff=orderData.ArriveTime - orderData.OrderDate;

to get the difference as a TimeSpan , for example :

var diff=orderData.ArriveTime - orderData.OrderDate;
var inRange= (diff>=TimeSpan.FromMinutes(10) && diff<TimeSpan.FromHours(2));
return inRange;

The difference between two dates is a duration, not a date. In .NET that duration is represented by the TimeSpan class. You can generate TimeSpan values using its constructor, or through methods like FromHours and FromMinutes

If OrderDate and ArriveTime are DateTime? , you'll get a TimeSpan? instead of TimeSpan . If any of those values is null, the difference will also be null.

In this example :

class Order{
    public DateTime? OrderDate{get;set;}
    public DateTime? ArriveTime{get;set;}
}

var orderData=new Order{};
TimeSpan? diff=orderData.ArriveTime - orderData.OrderDate;

diff is null . Both comparisons will return false so inRange will be false