Nullable(Of Single) VB.NET - Setting = 0 results in Nothing

[BobRoyAce]

I am using VB.NET and I have a variable that is defined as Nullable(Of
Single) as follows:

Dim fMyNullableSing le as Nullable(Of Single)

Then, I have another variable as follows:

Dim fCumulativeExpe ctedAmt As Single = 0

When I make the following assignment:

fMyNullableSing le = fCumulativeExpe ctedAmt

the end result is that fMyNullableSing le is Nothing. So, later, when I
try to assign it to another non-nullable variable, it fails.For
example...

Dim fMyNonNullableS ingle as Single
fMyNonNullableS ingle = fMyNullableSing le

causes an Exception.

How do I correct this?

[rowe_newsgroups]

Re: Nullable(Of Single) VB.NET - Setting = 0 results in Nothing

I am using VB.NET and I have a variable that is defined as Nullable(Of

Single) as follows:
>
  Dim fMyNullableSing le as Nullable(Of Single)
>
Then, I have another variable as follows:
>
  Dim fCumulativeExpe ctedAmt As Single = 0
>
When I make the following assignment:
>
  fMyNullableSing le = fCumulativeExpe ctedAmt
>
the end result is that fMyNullableSing le is Nothing.

I don't get that, when I assign zero to the Nullable(Of Single) it
returns zero:

////////////
Module Module1

Sub Main()
Dim s As Nullable(Of Single)
Dim s2 As Single = 0

Console.WriteLi ne(s.HasValue)
If s.HasValue Then Console.WriteLi ne(s.Value)

s = s2

Console.WriteLi ne(s.HasValue)
If s.HasValue Then Console.WriteLi ne(s.Value)

Console.Read()
End Sub

End Module
////////////

So, later, when I
try to assign it to another non-nullable variable, it fails.For
example...
>
  Dim fMyNonNullableS ingle as Single
  fMyNonNullableS ingle = fMyNullableSing le
>
causes an Exception.
>
How do I correct this?

It should cause an exception - that's an invalid cast. Simply do the
following to correct the problem:

//////////////
fMyNonNullableS ingle = fMyNullableSing le.Value
//////////////

Thanks,

Seth Rowe [MVP]

http://sethrowe.blogspot.com/

[BobRoyAce]

Re: Nullable(Of Single) VB.NET - Setting = 0 results in Nothing

I don't get that, when I assign zero to the Nullable(Of Single) it

returns zero:
>

I erred in not mentioning that the setting was happening in a Property
Set, and therein was the problem. The code that I had there was
checking, incorrectly, to see if the new value was different from the
existing value, and only setting the property if it was actually
different. Well, the code to check for difference did not use
the .Equals method of the Nullable type, and so was never setting the
property equal to ZERO! My mistake...

  Dim fMyNonNullableS ingle as Single
  fMyNonNullableS ingle = fMyNullableSing le

>

causes an Exception.

>

How do I correct this?

>
It should cause an exception - that's an invalid cast. Simply do the
following to correct the problem:
>
//////////////
fMyNonNullableS ingle = fMyNullableSing le.Value
//////////////

I have equated variables like this many times, without the
explicit .Value at the end of the Nullable one, with no known
problems. Perhaps it's just more "proper" to use the .Value?