Visual Basic: dynamically create objects using a string as the name

Question

Is there a way to dynamically create an object using a string as the class name?

I\'ve been off VB for several years now, but to solve a problem in another language,

Answer 1

Here is a really easy way I have found while rummaging through the internet:

dynamicControl = Activator.CreateInstance(Type.GetType("MYASSEMBLYNAME." + controlNameString))

Answer 2

I'm pretty sure Activator is used for remoting. What you want to do is use reflection to get the constor and invoke it here's an example http://www.eggheadcafe.com/articles/20050717.asp

EDIT: I was misguided about Activator until jwsample corrected me.

I think the problem your having is that your assembly is the one that GetType is using to try and find Button. You need to call it from the right assembly.

This should do it

Dim asm As System.Reflection.Assembly = System.Reflection.Assembly.LoadWithPartialName("System.Windows.Forms")


Dim obj As Object = Activator.CreateInstance(asm.GetType("System.Windows.Forms.Button"))

Answer 3

This will likely do what you want / tested working; switch the type comment at the top to see.

Imports System.Reflection

Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
    '            Dim fullyQualifiedClassName as String = "System.Windows.Forms.TextBox"
    Dim fullyQualifiedClassName As String = "System.Windows.Forms.Button"
    Dim o = fetchInstance(fullyQualifiedClassName)
    ' sometime later where you can narrow down the type or interface...
    Dim b = CType(o, Control)
    b.Text = "test"
    b.Top = 10
    b.Left = 10
    Controls.Add(b)
End Sub

Private Function fetchInstance(ByVal fullyQualifiedClassName As String) As Object
    Dim nspc As String = fullyQualifiedClassName.Substring(0, fullyQualifiedClassName.LastIndexOf("."c))
    Dim o As Object = Nothing
    Try
        For Each ay In Assembly.GetExecutingAssembly().GetReferencedAssemblies()
            If (ay.Name = nspc) Then
                o = Assembly.Load(ay).CreateInstance(fullyQualifiedClassName)
                Exit For
            End If
        Next
    Catch
    End Try
    Return o
End Function

Answer 4

Take a look at the Activator.CreateInstance(Type) method.

If your input is the name of a class you should be able do this:

Dim obj As Object = Activator.CreateInstance(GetType("Name_Of_Your_Class")) 

You'll have to fiddle with the GetType call to make sure you give it enough information but for most cases just the name of the class should work.