Private Sub TextBox3_KeyPress(ByVal sender As Object, ByVal e As _
      System.Windows.Forms.KeyPressEventArgs) Handles TextBox3.KeyPress
        Zeichne()
    End Sub

    Public Sub Zeichne()
        If TextBox1.Text <> "" And TextBox2.Text <> "" And TextBox3.Text _
          <> "" And TextBox4.Text <> "" And TextBox5.Text <> "" And _
          TextBox6.Text <> "" Then
 
            ' Wenn alle Textboxen einen Wert haben. 
            Dim Pen As New Pen(Color.Blue, 2)
            Dim g As Graphics = Me.TabControl1.CreateGraphics
 
            ' Zeichne
            With g
                .DrawLine(Pen, 100, 100, 220, 300)
            End With
        End If
    End Sub

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