สอบถามเกี่ยวกับ ComboBox , Dropdown ใส่ข้อมูลแล้วไม่ขึ้นครับ

 Private Sub Button4_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button4.Click
        CorralBindingSource.MovePrevious()
    End Sub

    Private Sub Button5_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button5.Click
        CorralBindingSource.MoveNext()
    End Sub

    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
        CorralBindingSource.AddNew()
    End Sub

    Private Sub Button2_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button2.Click
        CorralBindingSource.EndEdit()
        CorralTableAdapter.Update(DatabasProjectDataSet.Corral)
    End Sub

    Private Sub Button3_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button3.Click
        CorralBindingSource.RemoveCurrent()
    End Sub

    Private Sub Button6_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button6.Click
        Me.Close()
    End Sub

    Private Sub CorralIDComboBox_SelectedIndexChanged(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles CorralIDComboBox.SelectedIndexChanged
        Dim cor As String = CorralIDComboBox.Text
        CorralIDComboBox.Items.Add(CorralIDComboBox.Text)
    End Sub
End Class