title: Vb.net windows form, cannot open another main form when it is already open
body: <p>In this case, after I click the button from the second form, it open the another mainform even it already exists. what should i do?</p>
  <p>//MainForm form</p>
  <pre><code>Private Sub Button2_Click(sender As Object, e As EventArgs) Handles btn_meron.Click
      Dim vartxt = &quot;Meron&quot;
      Dim frm_docpopup As New frm_Docs_PopUp(vartxt)
      frm_docpopup.ShowDialog()
  End Sub
  </code></pre>
  <p>//Second Form</p>
  <pre><code>Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
      Dim vartxt = Label5.Text
      Dim totalAmount = Label3.Text
      Dim frm_mainform As New MainForm(vartxt, totalAmount)
      frm_mainform.Show()
      Me.Hide()
  End Sub
  </code></pre>