Identical If () and If give different results.

Question

What is the difference in the two code blocks below? I expected them to return the same result, but they do not.

In the case where xml. @Type = "null", I want PatientMetricTypeID (zero integer) to be Nothing.

Block # 1: If ()

In this case, it ends as 0. It seems that Nothing is considered as a whole and is not converted to 0. I can understand why this can happen, but not completely ... I would like to understand exactly how this works, and if there is workaround.

    Dim PatientMetricTypeID As Integer? = If(xml.@Type = "null",
                                 Nothing,
                                 CType([Enum].Parse(GetType(PatientMetricTypes), xml.@Type), Integer))

Block # 2: If

In this case, it ends as "No" - the expected behavior.

    Dim PatientMetricTypeID As Integer?

    If xml.@Type = "null" Then
        PatientMetricTypeID = Nothing
    Else
        PatientMetricTypeID = CType([Enum].Parse(GetType(PatientMetricTypes), xml.@Type), Integer)
    End If

Answer 1

If Integer, Integer?.

VB.Net Nothing null; # default(T), T - , .
MSDN:

(Visual Basic)

.

If(..., Nothing, SomeInteger), If Integer, Nothing 0.
If Integer?, Nothing New Integer?().

. .

Answer 2

. :

... = If(xml.@Type = "null", DirectCast(Nothing, Integer?), ...)

Microsoft :

• https://connect.microsoft.com/VisualStudio/feedback/details/496905/if-operator-not-returning-a-nullable-type

VB.

Answer 3

My suggestion is to use Integer?inside CTypeinsteadInteger