How to mimic the locked property of combobox in visual basic .net?

Try this:

Private comboLocked As Boolean
Private comboIndex As Integer = 1

    Private Sub ComboBox1_SelectedIndexChanged(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles ComboBox1.SelectedIndexChanged

        If comboLocked Then
            ComboBox1.SelectedIndex = comboIndex
        Else
            comboIndex = ComboBox1.SelectedIndex
        End If
    End Sub

SoMoS

An addition to SoMoS code:

Private comboLocked As Boolean
Private comboIndex As Integer

'Capture the selected index in the mousedown
Private Sub ComboBox1_MouseDown(ByVal sender As Object, ByVal e As System.Windows.Forms.MouseEventArgs) Handles ComboBox1.MouseDown
         comboIndex = ComboBox1.SelectedIndex
    End Sub

    Private Sub ComboBox1_SelectedIndexChanged(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles ComboBox1.SelectedIndexChanged

        If comboLocked Then
            ComboBox1.SelectedIndex = comboIndex
        End If
    End Sub

This is a workable solution, but I think Microsoft's note is better, simply don't allow user to select the
item, just like in vb6, user even can't move the mouse over the items.
But I don't know how to do that in MouseDown event.

    Private m_ReadOnly As Boolean

    'TODO stimulate Canceling the selection in the MouseDown Event.
    Private m_intSelectedValue As Integer = -1

    Public Property MyReadOnly() As Boolean
        Get
            Return m_ReadOnly
        End Get
        Set(ByVal Value As Boolean)
            m_ReadOnly = Value
            If m_ReadOnly Then
                Me.DropDownStyle = ComboBoxStyle.DropDownList
                'Me.Enabled = False

            Else
                Me.DropDownStyle = ComboBoxStyle.DropDown
                'Me.Enabled = True

            End If
        End Set
    End Property

    Private Sub ComboBoxEx_MouseDown(ByVal sender As Object, ByVal e As System.Windows.Forms.MouseEventArgs) Handles MyBase.MouseDown
        m_intSelectedValue = CType(sender, ComboBox).SelectedIndex
    End Sub

    Private Sub ComboBoxEx_SelectedIndexChanged(ByVal sender As Object, ByVal e As System.EventArgs) Handles MyBase.SelectedIndexChanged
        If m_ReadOnly Then
            If m_intSelectedValue <> -1 Then
                CType(sender, ComboBox).SelectedIndex = m_intSelectedValue
                m_intSelectedValue = -1
            End If
        End If
    End Sub