When you populate a combo you load it with data that normally comes in the form of a code and a description - but the combo is only interested in the description. By creating a class derived from a combo, with additional properties, you can use it to keep the codes as well. When the user selects a description, you can get the code from the control. Here's how I do it:
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Public Class ComboControl : Inherits System.Windows.Forms.ComboBox
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Private _CodeDescriptions As New Dictionary(Of String, String)
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Private _DescriptionCodes As New Dictionary(Of String, String)
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Private _AllowNone As Boolean
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Private _AllowAny As Boolean
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Private _ContextFlag As String
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Public Sub Clear()
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_CodeDescriptions.Clear()
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_DescriptionCodes.Clear()
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Me.Items.Clear()
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End Sub
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Public Property AllowAny() As Boolean
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Get
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AllowAny = _AllowAny
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End Get
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Set(ByVal value As Boolean)
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_AllowAny = value
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End Set
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End Property
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Public Property AllowNone() As Boolean
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Get
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AllowNone = _AllowNone
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End Get
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Set(ByVal value As Boolean)
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_AllowNone = value
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End Set
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End Property
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Public Property ContextFlag() As String
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Get
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ContextFlag = _ContextFlag
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End Get
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Set(ByVal value As String)
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_ContextFlag = value
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End Set
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End Property
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Public Sub Add(ByVal Code As String, ByVal Description As String)
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If _CodeDescriptions.Count = 0 And AllowNone Then
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Me.Items.Add("<None>")
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End If
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If _CodeDescriptions.Count = 0 And AllowAny Then
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Me.Items.Add("<Any>")
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End If
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Me.Items.Add(Description)
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_CodeDescriptions.Add(Code, Description)
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If Not _DescriptionCodes.ContainsKey(Description) Then ' suppress duplicates
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_DescriptionCodes.Add(Description, Code)
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End If
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End Sub
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Public Property Code() As String
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Get
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If Me.SelectedItem IsNot Nothing AndAlso Me.SelectedItem.ToString <> "" Then
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If _DescriptionCodes.ContainsKey(Me.SelectedItem.ToString) Then
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Return (_DescriptionCodes(Me.SelectedItem.ToString))
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Else
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Return ""
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End If
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Else
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Return ""
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End If
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End Get
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Set(ByVal value As String)
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Dim SelectedItem As String = ""
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If value <> "" Then
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If _CodeDescriptions.TryGetValue(value, SelectedItem) Then
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Me.SelectedItem = SelectedItem
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Else
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Add(value, "Unknown code " & value)
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Me.SelectedItem = value
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End If
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End If
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End Set
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End Property
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Public Sub RemoveElement(ByVal Name As String)
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Code = Name
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Items.RemoveAt(SelectedIndex)
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Dim Description = _CodeDescriptions(Name)
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_CodeDescriptions.Remove(Name)
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_DescriptionCodes.Remove(Description)
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End Sub
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End Class
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Loading the combo is easy. Here's an example:
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ccDefaultFrequencies.Clear()
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For Each objFrequency In objVisitFrequencies.Values
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With objFrequency
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ccDefaultFrequencies.Add(.FrequencyId, .Description)
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End With
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Next
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Having loaded the combo, it is easy to set an appropriate value:
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ccDefaultFrequencies.Code = "WEEK"
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- and picking up a selected value is correspondingly straightforward:
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DefaultFrequency = ccDefaultFrequencies.Code
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AllowAny and AllowNone permit the user to select either Any or None (but not both, they are mutually exclusive. Both return an empty string for the code.
