Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As _
      System.EventArgs) Handles Button1.Click, Button2.Click
        Dim btn As Button = CType(sender, Button)
        If btn.Tag Is Nothing Then
            Dim frm = New Form2
            frm.Text = "Form2/" & btn.Name
            btn.Tag = frm
            frm.Tag = btn
            AddHandler frm.FormClosed, AddressOf frm_FormClosed
            frm.ControlBox = False
            frm.Show()
        End If
    End Sub
 
    Private Sub frm_FormClosed(ByVal sender As Object, ByVal e As _
      System.Windows.Forms.FormClosedEventArgs)
        Dim frm As Form = CType(sender, Form)
        CType(frm.Tag, Button).Tag = Nothing
    End Sub

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