I am working on a new ASP.Net 4.0 data driven app. In the DAL I check for NULL values on all my data and default to the proper data when NULL. I have a strange issue going on. Two dates are coming back - on one I need the time only. The First line of code for the full date works without fail - but the second line of code errors pointing to the format string but the strange part is that it errors on NULL values which does not use the format string and just returns Date.MinValue. When the second line gets data it formats the return correctly.
Dim dr As DataRow
.TourDate = IIf(dr.IsNull("tourdate"), Date.MinValue, Format(dr("tourdate"), "MM/dd/yyyy"))
.TourTime = IIf(dr.IsNull("tourtime"), Date.MinValue, Format(dr("tourtime"), "T"))
The error comes on the second line when dr("tourtime") is NULL - the erroe is: Argument 'Expression' is not a valid value.
IIf in VB.Net does not do short-circuit evaluation, so the Format call is being executed even if the value is null.
You need to use If:
.TourTime = If(dr.IsNull("tourtime"), Date.MinValue, Format(dr("tourtime"), "T"))
This is the same issue described here: Using VB.NET IIF I get NullReferenceException