Question

This is really more of an academic question, but where is this function defined? Within .NET, I’m used to working in an object oriented manner. However, if I define a VB.NET class as follows:

Public Class foo
    Public Sub showmessagebox()
        Dim i As Integer
        i = MsgBox("Message")
    End Sub
End Class

Is MsgBox defined in a class? I am not required to reference a static class or inherit from another class. I’m not even required to import a namespace. I did find this link from msdn. But my question remains, where is this defined and how does the CLR just load up a function?

Answer 1

If you enter MsgBox into Visual Studio and hit F12, you will see that it is in the Microsoft.VisualBasic namespace, in the Interaction module.

In fact, this information is also available (although a bit hidden) at the bottom of the MSDN page you referenced:

Namespace: Microsoft.VisualBasic
Module: Interaction
Assembly: Visual Basic Runtime Library (in Microsoft.VisualBasic.dll)

If you look into the References section of your project properties, you’ll see that the Microsoft.VisualBasic namespace is automatically imported. Since Interaction is a module, you can use its methods without having to qualify the module name (as opposed to static/Shared methods of a class).

As a side note: If you add a reference to Microsoft.VisualBasic.dll to a C# project, you can use Microsoft.VisualBasic.Interaction.MsgBox("Hello World"); there as well (although most C# users will prefer using the MessageBox class).