Build a Better CheckedListBox Control

• Download source files - 4.74 Kb
• Download demo project - 6.39 Kb
• Download redistributable DLL - 3.5 Kb

Problems

• Control forgets checked status of items when using a TabControl.
• Users are able to check or uncheck items.
• Cannot reference an item based on its index.

Solution

All of these problems can be rectified by using a custom control.

Custom Control

The code below adds the AutoCheck property, the same property that the CheckBox control has, to the CheckedListBox control. It also implements a bug fix, plus allows to reference items in the control just like you can reference them in a ComboBox. To create our BetterCheckedListBox control, create a new VB.NET Class Library Project and copy the following code into Class1.vb.

'Show the CheckedListBox icon in the Toolbox for our component

<ToolboxBitmap(GetType(CheckedListBox))> _
Public Class BetterCheckedListBox
Inherits System.Windows.Forms.CheckedListBox
'----------------------------------------------------------

' Class level variables 

'----------------------------------------------------------

 Dim AllowChecks As Boolean 'Controls whether checkstate can be changed

 Dim ChkMember As String 'The DataColumn to use for checkstate

 Dim dt As DataTable 'Data to display

'----------------------------------------------------------

' Bug Fix

'----------------------------------------------------------

' When the CheckedListBox control is in a Tabcontrol 

' and that the Datasource property is used to fill

' up the item list, setting the clb's visible property

' to false, then to true, or flipping the tabs would

' cause the clb to "forget" the checks.

'

' Implement Carl Mercier's workaround

' http://www.codeproject.com/cs/combobox/FixedCheckedListBox.asp

'----------------------------------------------------------

 Public Overloads Property DataSource() As Object
  Get
   'Return our datatable variable

   DataSource = CType(dt, Object)
  End Get
  Set(ByVal value As Object)
   'Set our datatable variable

   dt = CType(value, DataTable)
   LoadData()
  End Set
 End Property
 Private Function LoadData()
  Dim bufAllowChecks = AllowChecks
  If AllowChecks = False Then
   'This is needed so we can change checkstates

    AllowChecks = True
  End If
  'Clear items

  MyBase.Items.Clear()
  'Fill it again

  Dim i As Integer
  For i = 0 To dt.DefaultView.Count - 1
   'Determine whether to check each item or not

   If dt.Rows(i).Item(ChkMember) = "1" Or _
     dt.Rows(i).Item(ChkMember) = "True" Then
    MyBase.Items.Add(dt.DefaultView.Item(i), True)
   Else
    MyBase.Items.Add(dt.DefaultView.Item(i), False)
   End If
  Next
  AllowChecks = bufAllowChecks
 End Function
 'Added or deleted records won't show without a refresh

 Public Overrides Sub Refresh()
  LoadData()
 End Sub
'----------------------------------------------------------

' Allow / Lock Checkstate Functionality

'----------------------------------------------------------

' Only let users check or uncheck items when you let them. 

' Note that you can't programmatically check or uncheck

' items either unless AllowChecks is True.

'

' This is an emulation of the Checkbox control's AutoCheck

' property.

'----------------------------------------------------------

'Show our property under the Behavior section of the Properties window

'So that it can be set at design time

<System.ComponentModel.Description("Allow checkstate to be changed"), _
System.ComponentModel.Category("Behavior")> _
 Public Property AutoCheck() As Boolean
  Get
   'Return our checkstate variable

   AutoCheck = AllowChecks
  End Get
  Set(ByVal value As Boolean)
   'Set our checkstate variable

   AllowChecks = value
  End Set
 End Property
 'Override the ItemCheck event with our own

 Protected Overrides Sub OnItemCheck(ByVal ice As _
           System.Windows.Forms.ItemCheckEventArgs)
  'Allow checks to be changed only if AutoCheck = True

  If AllowChecks = False Then
   ice.NewValue = ice.CurrentValue
  End If
 End Sub
'----------------------------------------------------------

' Reference Item By It's Index Functionality

'----------------------------------------------------------

' Wouldn't it be nice if you could reference items in a

' CheckedListBox control just like you can with a 

' ComboBox? Well now you can!

'

' Obtain Checkstatus, Text, and Values via an items index

'----------------------------------------------------------

<System.ComponentModel.Description("Gets or sets the CheckMember")> _
 Public Property CheckMember() As String
  Get
   CheckMember = ChkMember
  End Get
  Set(ByVal value As String)
   ChkMember = value
  End Set
 End Property
<System.ComponentModel.Description("Gets or sets an items's checkstate")> _
 Public Property Checked(ByVal index As Integer) As Boolean
  Get
   'Search for the item in CheckedIndices to see if its checked or not

   If MyBase.CheckedIndices.IndexOf(index) <> -1 Then
    Checked = True
   Else
    Checked = False
   End If
  End Get
  Set(ByVal value As Boolean)
   'Set item's checkstate

   Dim bufAllowChecks = AllowChecks
   If AllowChecks = False Then
    AllowChecks = True
   End If
   MyBase.SetItemChecked(index, value)
   AllowChecks = bufAllowChecks
  End Set
 End Property
<System.ComponentModel.Description("Gets or sets an items's DisplayMember")> _
 Public Overloads Property Text(ByVal index As Integer) As String
  Get
   Text = dt.Rows(index).Item(MyBase.DisplayMember)
  End Get
  Set(ByVal value As String)
   dt.Rows(index).Item(MyBase.DisplayMember) = value
  End Set
 End Property
<System.ComponentModel.Description("Gets or sets an items's ValueMember")> _
 Public Property Value(ByVal index As Integer) As String
  Get
   Value = dt.Rows(index).Item(MyBase.ValueMember)
  End Get
  Set(ByVal value As String)
   dt.Rows(index).Item(MyBase.ValueMember) = value
  End Set
 End Property
End Class

Once this project is compiled, copy the output, BetterCheckedListBox.dll, to C:\Program Files\Microsoft Visual Studio .NET 2003\Common7\IDE\PublicAssemblies\.

Then right click on the Toolbox, choose 'Add/Remove', select BetterCheckedListBox, and click OK to add our custom control to the Toolbox.

Demo Project

To create our demo project, start a new VB.NET Windows Application Project and copy the following code into Form1.vb. Run the project, a screen shot of the demo is also shown below.

Public Class Form1
Inherits System.Windows.Forms.Form
#Region " Windows Form Designer generated code "
 Public Sub New()
  MyBase.New()
  InitializeComponent()
 End Sub
 Protected Overloads Overrides Sub _
   Dispose(ByVal disposing As Boolean)
  If disposing Then
   If Not (components Is Nothing) Then
    components.Dispose()
   End If
  End If
  MyBase.Dispose(disposing)
 End Sub
 Private components As System.ComponentModel.IContainer
 Friend WithEvents Button1 As System.Windows.Forms.Button
 Friend WithEvents BetterCheckedListBox1 As _
        BetterCheckedListBox.BetterCheckedListBox
 Friend WithEvents CheckBox1 As System.Windows.Forms.CheckBox
 Friend WithEvents TextBox1 As System.Windows.Forms.TextBox
 Friend WithEvents Label1 As System.Windows.Forms.Label
 Friend WithEvents Label2 As System.Windows.Forms.Label
 Friend WithEvents Label3 As System.Windows.Forms.Label
 Friend WithEvents TextBox2 As System.Windows.Forms.TextBox
 Friend WithEvents Label4 As System.Windows.Forms.Label
 Friend WithEvents TextBox3 As System.Windows.Forms.TextBox
<System.Diagnostics.DebuggerStepThrough()>_
 Private Sub InitializeComponent()
  Me.Button1 = New System.Windows.Forms.Button
  Me.BetterCheckedListBox1 = New _
    BetterCheckedListBox.BetterCheckedListBox
  Me.CheckBox1 = New System.Windows.Forms.CheckBox
  Me.TextBox1 = New System.Windows.Forms.TextBox
  Me.Label1 = New System.Windows.Forms.Label
  Me.Label2 = New System.Windows.Forms.Label
  Me.Label3 = New System.Windows.Forms.Label
  Me.TextBox2 = New System.Windows.Forms.TextBox
  Me.Label4 = New System.Windows.Forms.Label
  Me.TextBox3 = New System.Windows.Forms.TextBox
  Me.SuspendLayout()
  Me.Button1.Location = New System.Drawing.Point(24, 144)
  Me.Button1.Name = "Button1"
  Me.Button1.Size = New System.Drawing.Size(120, 23)
  Me.Button1.TabIndex = 2
  Me.Button1.Text = "Add New Person"
  Me.BetterCheckedListBox1.AutoCheck = True
  Me.BetterCheckedListBox1.CheckMember = Nothing
  Me.BetterCheckedListBox1.Location = New System.Drawing.Point(24, 24)
  Me.BetterCheckedListBox1.Name = "BetterCheckedListBox1"
  Me.BetterCheckedListBox1.Size = New System.Drawing.Size(120, 94)
  Me.BetterCheckedListBox1.TabIndex = 3
  Me.CheckBox1.Location = New System.Drawing.Point(24, 120)
  Me.CheckBox1.Name = "CheckBox1"
  Me.CheckBox1.Size = New System.Drawing.Size(120, 16)
  Me.CheckBox1.TabIndex = 5
  Me.CheckBox1.Text = "Lock CheckBoxes"
  Me.TextBox1.Location = New System.Drawing.Point(152, 24)
  Me.TextBox1.Name = "TextBox1"
  Me.TextBox1.TabIndex = 6
  Me.TextBox1.Text = ""
  Me.Label1.Location = New System.Drawing.Point(152, 8)
  Me.Label1.Name = "Label1"
  Me.Label1.Size = New System.Drawing.Size(100, 16)
  Me.Label1.TabIndex = 7
  Me.Label1.Text = "Checked:"
  Me.Label2.Location = New System.Drawing.Point(24, 8)
  Me.Label2.Name = "Label2"
  Me.Label2.Size = New System.Drawing.Size(100, 16)
  Me.Label2.TabIndex = 8
  Me.Label2.Text = "People:"
  Me.Label3.Location = New System.Drawing.Point(152, 56)
  Me.Label3.Name = "Label3"
  Me.Label3.Size = New System.Drawing.Size(100, 16)
  Me.Label3.TabIndex = 10
  Me.Label3.Text = "Text:"
  Me.TextBox2.Location = New System.Drawing.Point(152, 72)
  Me.TextBox2.Name = "TextBox2"
  Me.TextBox2.TabIndex = 9
  Me.TextBox2.Text = ""
  Me.Label4.Location = New System.Drawing.Point(152, 104)
  Me.Label4.Name = "Label4"
  Me.Label4.Size = New System.Drawing.Size(100, 16)
  Me.Label4.TabIndex = 12
  Me.Label4.Text = "Value:"
  Me.TextBox3.Location = New System.Drawing.Point(152, 120)
  Me.TextBox3.Name = "TextBox3"
  Me.TextBox3.TabIndex = 11
  Me.TextBox3.Text = ""
  Me.AutoScaleBaseSize = New System.Drawing.Size(5, 13)
  Me.ClientSize = New System.Drawing.Size(272, 190)
  Me.Controls.Add(Me.Label4)
  Me.Controls.Add(Me.TextBox3)
  Me.Controls.Add(Me.Label3)
  Me.Controls.Add(Me.TextBox2)
  Me.Controls.Add(Me.Label2)
  Me.Controls.Add(Me.Label1)
  Me.Controls.Add(Me.TextBox1)
  Me.Controls.Add(Me.CheckBox1)
  Me.Controls.Add(Me.BetterCheckedListBox1)
  Me.Controls.Add(Me.Button1)
  Me.Name = "Form1"
  Me.Text = "BetterCheckedListBox Demo"
  Me.ResumeLayout(False)
 End Sub
#End Region
 Dim dt As New DataTable
 Private Sub Button1_Click(ByVal sender As System.Object,_
          ByVal e As System.EventArgs) Handles Button1.Click
  Dim dr As DataRow = dt.NewRow
  dr(0) = "Person " & BetterCheckedListBox1.Items.Count + 1
  dr(1) = "x"
  dr(2) = 0 'Checked is False

  dt.Rows.Add(dr)
  'Force refresh in order to show changes

  BetterCheckedListBox1.Refresh()
 End Sub
 Private Sub Form1_Load(ByVal sender As System.Object,_
       ByVal e As System.EventArgs) Handles MyBase.Load
  'Load some items

  dt.Columns.Add("txt", GetType(String))
  dt.Columns.Add("val", GetType(String))
  dt.Columns.Add("chk", GetType(String))
  Dim i As Integer
  For i = 1 To 5
   Dim dr As DataRow = dt.NewRow
   dr(0) = "Person " & i
   dr(1) = i
   dr(2) = "True"
   dt.Rows.Add(dr)
  Next
  'Set DataBindings

  BetterCheckedListBox1.DisplayMember = "txt"
  BetterCheckedListBox1.ValueMember = "val"
  BetterCheckedListBox1.CheckMember = "chk"
  BetterCheckedListBox1.DataSource = dt
 End Sub
 Private Sub CheckBox1_CheckedChanged(ByVal sender As _
      System.Object, ByVal e As System.EventArgs) _
      Handles CheckBox1.CheckedChanged
  'Allow / Lock items

  BetterCheckedListBox1.AutoCheck = Not CheckBox1.Checked
 End Sub
 Private Sub BetterCheckedListBox1_SelectedIndexChanged(ByVal _
     sender As System.Object, ByVal e As _
     System.EventArgs) Handles _
     BetterCheckedListBox1.SelectedIndexChanged
  'Determine whether item is checked or not

  TextBox1.Text = BetterCheckedListBox1.Checked(BetterCheckedListBox1.SelectedIndex)
  TextBox2.Text = BetterCheckedListBox1.Text(BetterCheckedListBox1.SelectedIndex)
  TextBox3.Text = BetterCheckedListBox1.Value(BetterCheckedListBox1.SelectedIndex)
 End Sub
 Private Sub BetterCheckedListBox1_ItemCheck(ByVal _
        sender As Object, ByVal e As _
        System.Windows.Forms.ItemCheckEventArgs) _
        Handles BetterCheckedListBox1.ItemCheck
  TextBox1.Text = _
   BetterCheckedListBox1.Checked(BetterCheckedListBox1.SelectedIndex)
 End Sub
End Class

Deployment

Make sure the custom control created is strongly named. To do this, you must first generate a key file and tell the compiler to use it.

Generate a key file by running the following command at the Visual Studio Command Prompt:

sn -k C:\Better.snk

Then, add the following as the first line (under the Imports) in the AssemblyInfo.vb file of your Custom control project.

<Assembly: AssemblyKeyFileAttribute("Better.snk")>

That's it. The BetterCheckedListBox control can now be easily deployed to the Global Assembly Cache.