vb.net - Why is my Nullable(Of Int32) = 0 after I set it to Nothing? -

i think i'm missing fundamental nullable types. example open new understanding, @ least, maybe can 1 thing working right.

in class (a dialog form), declare:

property productstructureheaderkey int32? 

in class, declare instance of dialog , attempt set property line:

    dr.productstructureheaderkey = if(parentrow.cells(1).value nothing, nothing, int32.parse(parentrow.cells(1).value)) 

when line assigns nothing property, property equal 0. (and later, it's passing 0 db when want passing null.)

that's not expect , keep finding code (so, msdn, etc) looks i'm doing things right, clearly, i'm not. so, friends, doing wrong? how employ nullable types meet needs?

that's 1 of differences between c# , vb.net. in vb.net nothing not mean null default. assigning default value of int32 property 0. caused if-operator has infer type 2 values not property want assign.

instead use either if...else:

if parentrow.cells(1).value nothing     dr.productstructureheaderkey = nothing ' it's not 0 nothing else     dr.productstructureheaderkey = int32.parse(parentrow.cells(1).value) end if 

or force nullable new nullable(of int32):

dr.productstructureheaderkey = if(parentrow.cells(1).value nothing, new nullable(of int32), int32.parse(parentrow.cells(1).value)) 

further read: why there difference in checking null against value in vb.net , c#?