Question

I have this code:

dstCell.CELL_VALUE_INT = If(srcCell.CELL_VALUE_FLOAT IsNot Nothing,
                            Math.Round(CDbl(srcCell.CELL_VALUE_FLOAT)),
                            Nothing)

when srcCell.CELL_VALUE_FLOAT is Nothing it mysteriously evaluates to the True part!

Funny part is that a normal If statement correctly evaluates to the False part:

If (srcCell.CELL_VALUE_FLOAT IsNot Nothing) Then
    dstCell.CELL_VALUE_INT = Math.Round(CDbl(srcCell.CELL_VALUE_FLOAT))
Else
    dstCell.CELL_VALUE_INT = Nothing
End If

Any ideas?

Thank u!

EDIT:
CELL_VALUE_FLOAT is a Nullable(Of Double) and CELL_VALUE_INT is a Nullable(of Integer)

In Quickwatch the condition evaluates correclty to False, but when running the If() function evaluates to the True part.

Answer 1

Nothing in VB.NET is not fully equal to null in C#
It is more like default(T) where T is a Type.

' VB:
dim x as DateTime = DateTime.MinValue
If x Is Nothing then
    Console.WriteLine("True")
End if

' C#
var x = DateTime.MinValue
if (x == default(DateTime))
    Console.WriteLine("True");

if (x == null) ' throw a compile time error

And

dim x as Double = nothing ' x will be 0 (default for Double)

the build in inline if expects both return values to be the same type. So what you a really doing is:

dstCell.CELL_VALUE_INT = If(srcCell.CELL_VALUE_FLOAT IsNot Nothing,
                            Math.Round(CDbl(srcCell.CELL_VALUE_FLOAT)),
                            Convert.ToDouble(Nothing))

since the false part gets internally converted to double
and dstCell.CELL_VALUE_INT will be 0 instead of nothing.

Try this one:

dstCell.CELL_VALUE_INT = If(srcCell.CELL_VALUE_FLOAT IsNot Nothing,
                         Ctype(Math.Round(CDbl(srcCell.CELL_VALUE_FLOAT)), Integer?),
                         Nothing)