Public Class frmMain
 
    Private Sub M_BuchungEinlagerung_Click(ByVal sender As System.Object, ByVal _
      e As System.EventArgs) Handles M_BuchungEinlagerung.Click
        Try
            Dim sFormName As String = "frmEinlagerung"
            If Not FormIsLoaded(sFormName) Then
                Dim oForm As New frmEinlagerung
                With oForm
                    .MdiParent = Me
                    .Show()
                End With
            Else
                frmEinlagerung.BringToFront()
            End If
        Catch ex As Exception
            MessageBox.Show(ex.Message, "Fehler", MessageBoxButtons.OK, _
              MessageBoxIcon.Stop)
        End Try
    End Sub
 
    Private Sub M_BuchungAuslagerung_Click(ByVal sender As System.Object, ByVal _
      e As System.EventArgs) Handles M_BuchungAuslagerung.Click
        Try
            Dim sFormName As String = "frmAuslagerung"
            If Not FormIsLoaded(sFormName) Then
                Dim oForm As New frmAuslagerung
                With oForm
                    .MdiParent = Me
                    .Show()
                End With
            Else
                frmAuslagerung.BringToFront()
            End If
        Catch ex As Exception
            MessageBox.Show(ex.Message, "Fehler", MessageBoxButtons.OK, _
              MessageBoxIcon.Stop)
        End Try
    End Sub
 
End Class

Module modRoutinen
 
    Public Function FormIsLoaded(ByVal sName As String) As Boolean
 
        Dim bResult As Boolean = False
 
        ' alle geöffneten Forms durchlauden
        For Each oForm As Form In Application.OpenForms
            If oForm.Name.ToLower = sName.ToLower Then
                bResult = True
                Exit For
            End If
        Next
 
        Return (bResult)
 
    End Function
 
End Module