VB.Net/Language Basics/nullable

Check if nullable is null

  

Option Explicit On
Option Strict On
Class MyClass1
    Public numericValue As Integer?
    Public boolValue As Boolean? = True
    Public Function GetIntFromDatabase() As Integer?
        Return numericValue
    End Function
    Public Function GetBoolFromDatabase() As Boolean?
        Return boolValue
    End Function
End Class
Module Program
    Sub Main()
        Dim dr As New MyClass1()
        Dim i As Integer? = dr.GetIntFromDatabase()
        If (i.HasValue) Then
            Console.WriteLine("Value of "i" is: {0}", i.Value)
        Else
            Console.WriteLine("Value of "i" is undefined.")
        End If
        Dim b As Boolean? = dr.GetBoolFromDatabase()
        If (b.HasValue) Then
            Console.WriteLine("Value of "b" is: {0}", b.Value)
        Else
            Console.WriteLine("Value of "b" is undefined.")
        End If
    End Sub
End Module

Main with Nullable (Of T)

  
Class MyClass1
    Public numericValue As Nullable(Of Integer)
    Public boolValue As Nullable(Of Boolean) = True
    Public Function GetIntFromDatabase() As Nullable(Of Integer)
        Return numericValue
    End Function
    Public Function GetBoolFromDatabase() As Nullable(Of Boolean)
        Return boolValue
    End Function
    Public Shared Sub Main()
        Dim dr As New MyClass1()
        Dim i As Nullable(Of Integer) = dr.GetIntFromDatabase()
        If (i.HasValue) Then
            Console.WriteLine("Value of "i" is: {0}", i.Value)
        Else
            Console.WriteLine("Value of "i" is undefined.")
        End If
        Dim b As Nullable(Of Boolean) = dr.GetBoolFromDatabase()
        If (b.HasValue) Then
            Console.WriteLine("Value of "b" is: {0}", b.Value)
        Else
            Console.WriteLine("Value of "b" is undefined.")
        End If
    End Sub
End Class