MDI Form

總之作法大致就是這樣
把 Form 的 property 設一下, Menu 裡面的 Item click event 就是這麼寫…

Private Sub MenuItem3_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles MenuItem3.Click
  Dim frm As Form3 = New Form3
  If check(frm) Then Return
  frm.MdiParent = Me
  frm.Show()
End Sub

Private Function CeckExist(ByVal compareFrom As Form) As Boolean
  For Each f As Form In Me.MdiChildren
    If f.GetType().Equals(compareFrom.GetType()) Then
      f.BringToFront() ‘ f.Focus() 也可以
      Return True
    End If
  Next
  Return False
End Function