Public Class CBcustom
    Inherits ComboBox

    Dim pCBtasti As New List(Of Keys)

    ''' <summary>
    ''' Aggiunge un tasto che non chiude
    ''' la DopDownList
    ''' </summary>
    ''' <param name="Tasto">Keys.ecc</param>
    Public Sub TastoAdd(ByVal Tasto As Keys)
        pCBtasti.Add(Tasto)
    End Sub

    ''' <summary>
    ''' Rimuove un tasto che non chiude
    ''' la DopDownList
    ''' </summary>
    ''' <param name="Tasto">Keys.ecc</param>
    Public Sub TastoRemove(ByVal Tasto As Keys)
        pCBtasti.Remove(Tasto)
    End Sub

    Sub New()
        Me.DropDownStyle = ComboBoxStyle.DropDown
        Me.AutoCompleteMode = AutoCompleteMode.Suggest
        Me.AutoCompleteSource = AutoCompleteSource.ListItems
    End Sub

    Protected Overrides Function ProcessCmdKey(ByRef msg As System.Windows.Forms.Message, ByVal keyData As System.Windows.Forms.Keys) As Boolean
        If pCBtasti.Contains(keyData) = False Then
            Me.DroppedDown = False
        End If
        Return MyBase.ProcessCmdKey(msg, keyData)
    End Function

    Private Sub mostraDPList() Handles Me.TextChanged
        If Me.Focused Then
            If Me.Text = "" Then
                Me.DroppedDown = True
            End If
        End If
    End Sub

End Class