Public Class MDIForm
    Inherits System.Windows.Forms.Form
#Region " Vom Windows Form Designer generierter Code "
    Public Sub New()
        MyBase.New()
        InitializeComponent()
    End Sub
    Protected Overloads Overrides Sub Dispose(ByVal disposing As Boolean)
        If disposing Then
            If Not (components Is Nothing) Then
                components.Dispose()
            End If
        End If
        MyBase.Dispose(disposing)
    End Sub
    Private components As System.ComponentModel.IContainer
    Friend WithEvents btnPaste As System.Windows.Forms.Button
    Friend WithEvents btnOpenMDIChild As System.Windows.Forms.Button
    <System.Diagnostics.DebuggerStepThrough()> Private Sub InitializeComponent()
        Me.btnPaste = New System.Windows.Forms.Button
        Me.btnOpenMDIChild = New System.Windows.Forms.Button
        Me.SuspendLayout()
        Me.btnPaste.Location = New System.Drawing.Point(96, 0)
        Me.btnPaste.Name = "btnPaste"
        Me.btnPaste.Size = New System.Drawing.Size(96, 32)
        Me.btnPaste.TabIndex = 0
        Me.btnPaste.Text = "Einfügen"
        Me.btnOpenMDIChild.Location = New System.Drawing.Point(0, 0)
        Me.btnOpenMDIChild.Name = "btnOpenMDIChild"
        Me.btnOpenMDIChild.Size = New System.Drawing.Size(96, 32)
        Me.btnOpenMDIChild.TabIndex = 0
        Me.btnOpenMDIChild.Text = "Öffne MDIChild"
        Me.AutoScaleBaseSize = New System.Drawing.Size(5, 13)
        Me.ClientSize = New System.Drawing.Size(912, 477)
        Me.Controls.Add(Me.btnPaste)
        Me.Controls.Add(Me.btnOpenMDIChild)
        Me.IsMdiContainer = True
        Me.Name = "MDIForm"
        Me.Text = "MDIParent"
        Me.ResumeLayout(False)
    End Sub
#End Region
    Private Sub btnOpenMDIChild_Click(ByVal sender As System.Object, ByVal e As _
      System.EventArgs) Handles btnOpenMDIChild.Click
        ' MDI Child Form erstellen und zeigen
        Dim f As New frmMdiChild
        f.MdiParent = Me 'dem FrmChild mitteilen, zu welchem MDI Container es 
        ' gehört
        f.Show()
    End Sub
    Private Sub btnPaste_Click(ByVal sender As System.Object, ByVal e As _
      System.EventArgs) Handles btnPaste.Click
        For Each form As Form In Me.MdiChildren ' mit For Each durch das 
        ' Children Forms Array "gehen"; die var. "Form" ist vom Type "Form"
            If form.GetType Is GetType(frmMdiChild) Then ' ist die gefundene 
            ' Form vom Type "frmMdiChild"
                Dim path As String = Environment.GetEnvironmentVariable( _
                  "SYSTEMROOT") + "\winnt.bmp" ' Pfad für ein Bild
                CType(form, frmMdiChild).torbox.Image = Image.FromFile(path)
                CType(form, frmMdiChild).Label1.Text = path
                ' CType(form, frmMdiChild) = Die Var. "Form" ist vom Type Form, 
                ' da aber das MDI Child vom Type "frmMdiChild" ist, muss 
                ' diese in diesen Type umgewandelt werden. Da ja ein PictureBox 
                ' mit Namen "torbox" nur auf der Form "frmMdiChild" vorhanden 
                ' ist.
            End If
        Next
    End Sub
End Class

Public Class frmMdiChild
    Inherits System.Windows.Forms.Form
#Region " Vom Windows Form Designer generierter Code "
    Public Sub New()
        MyBase.New()
        InitializeComponent()
    End Sub
    Protected Overloads Overrides Sub Dispose(ByVal disposing As Boolean)
        If disposing Then
            If Not (components Is Nothing) Then
                components.Dispose()
            End If
        End If
        MyBase.Dispose(disposing)
    End Sub
    Private components As System.ComponentModel.IContainer
    Friend WithEvents Label1 As System.Windows.Forms.Label
    Friend WithEvents torbox As System.Windows.Forms.PictureBox
    <System.Diagnostics.DebuggerStepThrough()> Private Sub InitializeComponent()
        Me.Label1 = New System.Windows.Forms.Label
        Me.torbox = New System.Windows.Forms.PictureBox
        Me.SuspendLayout()
        Me.Label1.Location = New System.Drawing.Point(8, 320)
        Me.Label1.Name = "Label1"
        Me.Label1.Size = New System.Drawing.Size(824, 24)
        Me.Label1.TabIndex = 0
        Me.torbox.Location = New System.Drawing.Point(8, 8)
        Me.torbox.Name = "torbox"
        Me.torbox.Size = New System.Drawing.Size(424, 304)
        Me.torbox.TabIndex = 1
        Me.torbox.TabStop = False
        Me.AutoScaleBaseSize = New System.Drawing.Size(5, 13)
        Me.ClientSize = New System.Drawing.Size(848, 357)
        Me.Controls.Add(Me.torbox)
        Me.Controls.Add(Me.Label1)
        Me.Name = "frmMdiChild"
        Me.Text = "frmMdiChild"
        Me.ResumeLayout(False)
    End Sub
#End Region
End Class