Extensibility Question
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I'm creating a control that inherits from a combobox (infragistics 2 be exact). I am implementing most recently used functionality, where the last five entries entered into the combobox are persisted across all control instances in the application and are synced up at all times. All this is working fine and dandy, but I am having trouble coming up with a way to allow this to be fully extendable. I guess the biggest opstacle I see is that I am using a shared, derived queue class to manage the entries and a shared event used internally to allow the controls to allways be notified when to resync their list. I'm sure there is probably an easy way to accomodate this, but I have been looking at this screen way to long. 
Here is the source:
Imports Infragistics.Win.UltraWinEditors
Namespace Controls
''' -----------------------------------------------------------------------------
''' Project : Sheakley.Evolution.Windows.UI.Controls
''' Class : Evolution.Windows.UI.MRUComboBox
'''
''' Copyright (C) 2004, All Rights Reserved
''' -----------------------------------------------------------------------------
''' <summary>
''' Extends the EvolutionComboBox control in order to add mru list functionality.
''' </summary>
''' <remarks>
''' </remarks>
''' <history>
''' mpaul 12/10/2004 Created
''' </history>
''' -----------------------------------------------------------------------------
Public Class PolicyComboBox
Inherits UltraComboEditor
''' -----------------------------------------------------------------------------
''' Project : Sheakley.Evolution.Windows.UI.Controls
''' Class : Evolution.Windows.UI.Controls.MRUComboBox.MRUQueue
'''
''' Copyright (C) 2004, All Rights Reserved
''' -----------------------------------------------------------------------------
''' <summary>
''' Extends the System.Collections.Queue class in order to automatically purge items when the queue is full.
''' </summary>
''' <remarks>
''' </remarks>
''' <history>
''' mpaul 12/10/2004 Created
''' </history>
''' -----------------------------------------------------------------------------
Friend Class MRUQueue
Inherits System.Collections.Queue
''' -----------------------------------------------------------------------------
''' <summary>
''' Private attributes.
''' </summary>
''' <remarks>
''' </remarks>
''' <history>
''' mpaul 12/10/2004 Created
''' </history>
''' -----------------------------------------------------------------------------
Private _max As Integer
''' -----------------------------------------------------------------------------
''' <summary>
''' Ctor.
''' </summary>
''' <param name="max">Maximum allowed items in the queue at any given time</param>
''' <remarks>
''' </remarks>
''' <history>
''' mpaul 12/10/2004 Created
''' </history>
''' -----------------------------------------------------------------------------
Public Sub New(ByVal max As Integer)
_max = max
End Sub
''' -----------------------------------------------------------------------------
''' <summary>
''' Adds the item to the queue.
''' </summary>
''' <param name="obj">Object to add to the queue</param>
''' <remarks>
''' Removes the last item added if the maximum allowed items is reached.
''' </remarks>
''' <history>
''' mpaul 12/10/2004 Created
''' </history>
''' -----------------------------------------------------------------------------
Public Overrides Sub Enqueue(ByVal value As Object)
If Me.Count >= _max Then Me.Dequeue()
MyBase.Enqueue(value)
End Sub
End Class
''' -----------------------------------------------------------------------------
''' <summary>
''' Private attributes.
''' </summary>
''' <remarks>
''' </remarks>
''' <history>
''' mpaul 12/10/2004 Created
''' </history>
''' -----------------------------------------------------------------------------
Private Shared _mostRecentlyUsedList As MRUQueue
''' -----------------------------------------------------------------------------
''' <summary>
''' Public events.
''' </summary>
''' <remarks>
''' </remarks>
''' <history>
''' mpaul 12/10/2004 Created
''' </history>
''' -----------------------------------------------------------------------------
Private Shared Event ListChanged(ByVal sender As Object, ByVal e As EventArgs)
''' -----------------------------------------------------------------------------
''' <summary>
''' Private shared ctor.
''' </summary>
''' <remarks>
''' This constructor is only called once, the first time an instance of this class is requested.
''' </remarks>
''' <history>
''' mpaul 12/10/2004 Created
''' </history>
''' -----------------------------------------------------------------------------
Shared Sub New()
_mostRecentlyUsedList = New MRUQueue(10)
End Sub
''' -----------------------------------------------------------------------------
''' <summary>
''' Ctor.
''' </summary>
''' <remarks>
''' </remarks>
''' <history>
''' mpaul 12/10/2004 Created
''' </history>
''' -----------------------------------------------------------------------------
Public Sub New()
MyBase.New()
' first thing we need to do is load up our items collection from the shared queue.
LoadItemsFromQueue()
MyBase.MaxLength = 8 ' Policy #'s cannot be greater than eight digits.
MyBase.DropDownStyle = Infragistics.Win.DropDownStyle.DropDown
' wire up our event handler in order to be notified whenever the internal list changes.
AddHandler Me.ListChanged, AddressOf Me.MRUComboBox_ListChanged
End Sub
''' -----------------------------------------------------------------------------
''' <summary>
''' Handles the ListChanged event and re-populates the items collection from the queue.
''' </summary>
''' <remarks>
''' </remarks>
''' <history>
''' mpaul 12/10/2004 Created
''' </history>
''' -----------------------------------------------------------------------------
Private Sub MRUComboBox_ListChanged(ByVal sender As Object, ByVal e As EventArgs)
LoadItemsFromQueue()
End Sub
''' -----------------------------------------------------------------------------
''' <summary>
''' Adds the controls text value to the mru list.
''' </summary>
''' <remarks>
''' By default, uses the controls text value.
''' </remarks>
''' <history>
''' mpaul 12/10/2004 Created
''' </history>
''' -----------------------------------------------------------------------------
Public Overloads Sub Push()
Me.Push(MyBase.Text.Trim)
End Sub
''' -----------------------------------------------------------------------------
''' <summary>
''' Adds the specified value to the mru list.
''' </summary>
''' <remarks>
''' </remarks>
''' <history>
''' mpaul 12/10/2004 Created
''' </history>
''' -----------------------------------------------------------------------------
Public Overridable Overloads Sub Push(ByVal value As String)
If value.Trim <> String.Empty AndAlso Not _mostRecentlyUsedList.Contains(value) Then
' push our item to the queue and broadcast the event to notify all instances their
' internal lists need refreshed from the queue.
_mostRecentlyUsedList.Enqueue(value)
RaiseEvent ListChanged(Me, EventArgs.Empty)
End If
End Sub
''' -----------------------------------------------------------------------------
''' <summary>
''' Loads the items collections from the internal queue.
''' </summary>
''' <remarks>
''' </remarks>
''' <history>
''' mpaul 12/10/2004 Created
''' </history>
''' -----------------------------------------------------------------------------
Protected Overridable Sub LoadItemsFromQueue()
' this is added as a pre-caution. it seems that every so often, we lose the
' initial text value after this method runs.
Dim origVal As String = MyBase.Text
' first thing we need to do is wipe out our most recently used collection
' and grab a reference to the enumerator object.
MyBase.Items.Clear()
Dim enumerator As IEnumerator = _mostRecentlyUsedList.GetEnumerator()
' next, simply enumerate our collection and add our items to our list.
While enumerator.MoveNext()
MyBase.Items.Insert(0, enumerator.Current, enumerator.Current)
End While
MyBase.Text = origVal
End Sub
''' -----------------------------------------------------------------------------
''' <summary>
''' We need to discard any characters that are not numeric or control chars.
''' </summary>
''' <param name="e"></param>
''' <remarks>
''' </remarks>
''' <history>
''' mpaul 12/10/2004 Created
''' </history>
''' -----------------------------------------------------------------------------
Protected Overrides Sub OnKeyPress(ByVal e As System.Windows.Forms.KeyPressEventArgs)
If Not Char.IsDigit(e.KeyChar) AndAlso Not Char.IsControl(e.KeyChar) AndAlso Not Char.IsWhiteSpace(e.KeyChar) Then
e.Handled = True
End If
End Sub
''' -----------------------------------------------------------------------------
''' <summary>
''' Gets the policy number.
''' </summary>
''' <value></value>
''' <remarks>
''' </remarks>
''' <history>
''' mpaul 12/10/2004 Created
''' </history>
''' -----------------------------------------------------------------------------
Public Shadows ReadOnly Property Value() As Long
Get
Dim tryParse As Long = 0
If MyBase.Text.Trim <> String.Empty Then
If IsNumeric(MyBase.Text.Trim) Then
Try
tryParse = System.Int64.Parse(MyBase.Text.Trim)
Catch ex As Exception
MyBase.Text = String.Empty
End Try
Else
MyBase.Text = String.Empty
End If
End If
Return tryParse
End Get
End Property
End Class
End Namespace