Interfaces sind

Public Interface PlugIn
    Function Load() As Boolean
 
    Function Show() As Boolean
 
    Function Close() As Boolean
End Interface

Public Class Form1
    Inherits System.Windows.Forms.Form
 
#Region " Vom Windows Form Designer generierter Code "
 
    Private PlugIn As MyInterFaces.PlugIn
 
    Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As _
      System.EventArgs) Handles MyBase.Load
        ' alle PlugIns müssen in den anwendungsordner -> unterordner PlugIns
        Dim PlugIns() As String = Directory.GetFiles(Application.StartupPath & _
          "\PlugIns")
        If PlugIns.Length = 0 Then
            ' kein PlugIn gefunden
        Else
            ' mindestens ein PlugIn gefunden
            ' ich berücksichtige hier auch nur eines!!
            Dim f1 As FileStream = New FileStream(PlugIns(0), FileMode.Open)
            Dim rawAssemblyBytes1(f1.Length) As Byte
            f1.Read(rawAssemblyBytes1, 0, CType(f1.Length, Integer))
            f1.Close()
            Dim a As [Assembly] = AppDomain.CurrentDomain.Load( _
              rawAssemblyBytes1)
 
            PlugIn = a.CreateInstance(a.EntryPoint.ReflectedType.Namespace & _
              ".PlugInClass")
        End If
    End Sub
 
    Private Sub btnLoad_Click(ByVal sender As System.Object, ByVal e As _
      System.EventArgs) Handles btnLoad.Click
        PlugIn.Load()
    End Sub
 
    Private Sub btnShow_Click(ByVal sender As System.Object, ByVal e As _
      System.EventArgs) Handles btnShow.Click
        PlugIn.Show()
    End Sub
 
    Private Sub btnClose_Click(ByVal sender As System.Object, ByVal e As _
      System.EventArgs) Handles btnClose.Click
        PlugIn.Close()
    End Sub
End Class

Public Class PlugInClass
    Implements MyInterFaces.PlugIn
 
    Private frm As FrmMain
    Public Function Close() As Boolean Implements MyInterFaces.PlugIn.Close
        Try
            frm.Close()
            frm.Dispose()
            frm = Nothing
            Return True
        Catch ex As Exception
            Return False
        End Try
    End Function
 
    Public Function Load() As Boolean Implements MyInterFaces.PlugIn.Load
        Try
            frm = New FrmMain
            Return True
        Catch ex As Exception
            Return False
        End Try
 
    End Function
 
    Public Function Show() As Boolean Implements MyInterFaces.PlugIn.show
        Try
            frm.ShowDialog()
            Return True
        Catch ex As Exception
            Return False
        End Try
    End Function
End Class