Introduction to the Checked List Boxes

Description

A checked list box combines the functionalities of the list box and the check box controls. As a list box, it displays each of its items on a line. If there are too many items than the control can display, it would be equipped with a vertical scroll bar.

To select an item in the list, the user can click the desired string. The most important and obvious characteristic of the checked list box is that each item displays a check box on its left. This box allows the user to select or deselect each item. To select an item, the user must click its box and not its string, to indicate an explicit selection. This draws a check mark in the box. As described with the check box control, the user can deselect an item by removing the check mark. The check mark indicates that an item is selected and the absence of the check mark indicates the contrary. Like the check box control, you can allow the user to indicate a "half-checked" item. In this case, a check box can appear unchecked, checked, or grayed.

1. Start a new Windows Application named AltairRealtors1
2. On the main menu, click Project ->Add Class...
3. Set the Name to AvailableProperty and click Add
4. Change the file as follows:
    

   Public Class AvailableProperty Private propNbr As Long Private propType As String Private adrs As String Private ct As String Private stt As String Private zip As Integer Private beds As Byte Private baths As Single Private mValue As Double Public Property PropertyNumber() As Long Get Return propNbr End Get Set(ByVal value As Long) propNbr = value End Set End Property Public Property PropertyType() As String Get Return propType End Get Set(ByVal value As String) propType = value End Set End Property Public Property Address() As String Get Return adrs End Get Set(ByVal value As String) adrs = value End Set End Property Public Property City() As String Get Return ct End Get Set(ByVal value As String) ct = value End Set End Property Public Property State() As String Get Return stt End Get Set(ByVal value As String) stt = value End Set End Property Public Property ZIPCode() As Integer Get Return zip End Get Set(ByVal value As Integer) zip = value End Set End Property Public Property Bedrooms() As Byte Get Return beds End Get Set(ByVal value As Byte) beds = value End Set End Property Public Property Bathrooms() As Single Get Return baths End Get Set(ByVal value As Single) baths = value End Set End Property Public Property MarketValue() As Double Get Return mValue End Get Set(ByVal value As Double) mValue = value End Set End Property Public Sub New() End Sub Public Sub New(ByVal code As Long, ByVal type As String, _ ByVal addrs As String, ByVal cty As String, _ ByVal states As String, ByVal zCode As Integer, _ ByVal bedroom As Byte, ByVal bathroom As Single, _ ByVal value As Double) propNbr = code propType = type adrs = Address ct = City stt = State zip = zCode beds = bedroom baths = bathroom mValue = value End Sub End Class

5. In the Solution Explorer, right-click Form1.vb and click Rename
6. Type RealEstate.vb and press Enter twice

To support checked list boxes, the .NET Framework provides the CheckedListBox class. At design time, to add a checked list box to your application, from the Common Controls section of the Toolbox, click the CheckedListBox button and click the form or the container that would host the control. To programmatically create a checked list box, declare a variable of type CheckedListBox, use the new operator to allocate memory for it, and add it to the Controls collection of its parent. Here is an example:

Imports System.Drawing
Imports System.Windows.Forms

Module Exercise

    Public Class Starter
        Inherits Form

        private lbxPersonalRelationships as   CheckedListBox

        Dim components As System.ComponentModel.Container

        Public Sub New()
            InitializeComponent()
        End Sub

        Public Sub InitializeComponent()

            lbxPersonalRelationships = New CheckedListBox()
            lbxPersonalRelationships.Location = New Point(12, 12)

            Controls.Add(lbxPersonalRelationships)

        End Sub

    End Class

    Function Main() As Integer

        Dim frmStart As Starter = New Starter

        Application.Run(frmStart)

        Return 0
    End Function

End Module

This would produce:

1. Design the form as follows:
    

   Control Text Name Other Properties Label Altair Realtors   BorderStyle: FixedSingle Font: Times New Roman, 21.75pt, style=Bold AutoSize: False TextAlign: MiddleCenter Label Types to Show     CheckedListBox   lbxPropertiesTypes   Button Show btnShow   Label Properties_______   Font: Garamond, 15.75pt, style=Bold Label Prop #     Label Address     Label City     Label State     Label ZIP Code     Label Beds     Label Baths     Label Market Value     ListBox   lbxPropertyNumbers   ListBox   lbxAddresses   ListBox   lbxCities   ListBox   lbxStates   ListBox   lbxZIPCodes   ListBox   lbxBedrooms   ListBox   lbxBathrooms   ListBox   lbxMarketValues   Button Close btnClose

2. Save the form

The CheckedListBox class is derived from the ListBox class. This means that the checked list box possesses all the public (and protected) characteristics of the list box and its parent the ListControl class. This control also uses the HorizontalScrollbar and the HorizontalExtent properties that behave exactly as we reviewed for the list box. It also uses the SelectionMode property with the same behavior as that of the list box.

As seen for the list box, the primary aspect of a checked list box is its list of items. At design time, to create the list of items of a checked list box, access its Properties window, and click the ellipsis button to open the String Collection Editor. Type each item followed by a carriage return. After creating the list, click OK. To programmatically create the list of items, access the Items property. The list is created from the nested ObjectCollection class that implements the IList, the ICollection, and the IEnumerable interfaces. This means that the CheckedListBox.ObjectCollection class behaves the same as the ListBox.ObjectCollection class. Here is an example:

Public Sub InitializeComponent()

            lbxPersonalRelationships = New CheckedListBox()
            lbxPersonalRelationships.Location = New Point(12, 12)

            lbxPersonalRelationships.Items.Add("Family Member")
            lbxPersonalRelationships.Items.Add("Friend")
            lbxPersonalRelationships.Items.Add("Classmate")
            lbxPersonalRelationships.Items.Add("Business Partner")
            lbxPersonalRelationships.Items.Add("Simple Acquaintance")
            lbxPersonalRelationships.Items.Add("Undefined")

            Controls.Add(lbxPersonalRelationships)

End Sub

This would produce:

Remember that you can also add an array of items by calling the AddRange() and you can insert an item using the Insert() method.

1. On the form, click the checked list box
2. In the Properties window, click Items and click its ellipsis button
3. In the String Collection Editor, type Single Families and press Enter
4. Type Townhouses and press Enter
5. Type Condominiums and press Enter
6. Type Trailers and click OK

As mentioned already, the main difference between a list box and a checked list is the presence of check marks in the former. When using the control, the user can click one or more check boxes. Here is an example:

After the user has clicked a few check boxes, you may want to find out which ones are checked. The checked list box provides two techniques you can use.

As seen for the list box, each item of the control has an index. When one, a few, or all items have been checked (those that display a check mark), the indices of the checked items are stored in a collection represented by the CheckedIndices property. This property is based on the nested CheckedIndexCollection collection class. The CheckedIndexCollection class implements the IList, the ICollection, and the IEnumerable interfaces.

The identifications of the checked items are stored in a collection represented by the CheckedItems property. This property is based on the nested CheckedItemCollection class. The CheckedItemCollection class implements the IList, the ICollection, and the IEnumerable interfaces. This implies that you can use it to get the number of selected items.

When the user has clicked item to put a check mark on it, the control fires the ItemCheck event.

As you can see, the event is carried by the ItemCheckEventArgs class.

One of the most important operations to perform on a list of selected items is to find out whether a particular item is checked. To get this information, the CheckedItemCollection class provides a method named Contains. Its syntax is:

Public Function Contains(item As Object) As Boolean

This method takes as argument a value that can identify an item from the checked list box. If the item is found and it is checked, this method returns true. Otherwise, it returns false. 

1. Double-click an unoccupied area of the form to generate its Load event
2. Change the file as follows:
    

   Public Class RealEstate Private Properties(14) As AvailableProperty Private Sub RealEstate_Load(ByVal sender As System.Object, _ ByVal e As System.EventArgs) _ Handles MyBase.Load Properties(0) = New AvailableProperty() Properties(0).PropertyNumber = 602138 Properties(0).PropertyType = "Single Family" Properties(0).Address = "11604 Aldora Avenue" Properties(0).City = "Baltimore" Properties(0).State = "MD" Properties(0).ZIPCode = 21205 Properties(0).Bedrooms = 5 Properties(0).Bathrooms = 3.5F Properties(0).MarketValue = 265880 Properties(1) = New AvailableProperty() Properties(1).PropertyNumber = 749562 Properties(1).PropertyType = "Townhouse" Properties(1).Address = "495 Parker House Terrace" Properties(1).City = "Gettysburg" Properties(1).State = "WV" Properties(1).ZIPCode = 26201 Properties(1).Bedrooms = 3 Properties(1).Bathrooms = 2.5F Properties(1).MarketValue = 225500 Properties(2) = New AvailableProperty() Properties(2).PropertyNumber = 304750 Properties(2).PropertyType = "Condominium" Properties(2).Address = "5900 24th Street NW #812" Properties(2).City = "Washington" Properties(2).State = "DC" Properties(2).ZIPCode = 20008 Properties(2).Bedrooms = 1 Properties(2).Bathrooms = 1.0F Properties(2).MarketValue = 388665 Properties(3) = New AvailableProperty() Properties(3).PropertyNumber = 682630 Properties(3).PropertyType = "Single Family" Properties(3).Address = "6114 Costinna Avenue" Properties(3).City = "Martinsburg" Properties(3).State = "WV" Properties(3).ZIPCode = 25401 Properties(3).Bedrooms = 4 Properties(3).Bathrooms = 3.5F Properties(3).MarketValue = 325000 Properties(4) = New AvailableProperty() Properties(4).PropertyNumber = 480750 Properties(4).PropertyType = "Condominium" Properties(4).Address = "10710 Desprello Street #10D" Properties(4).City = "Rockville" Properties(4).State = "MD" Properties(4).ZIPCode = 20856 Properties(4).Bedrooms = 1 Properties(4).Bathrooms = 1.0F Properties(4).MarketValue = 528445 Properties(5) = New AvailableProperty() Properties(5).PropertyNumber = 209475 Properties(5).PropertyType = "Single Family" Properties(5).Address = "519D Estuardo Way" Properties(5).City = "Silver Spring" Properties(5).State = "MD" Properties(5).ZIPCode = 20906 Properties(5).Bedrooms = 2 Properties(5).Bathrooms = 1.0F Properties(5).MarketValue = 325995 Properties(6) = New AvailableProperty() Properties(6).PropertyNumber = 304185 Properties(6).PropertyType = "Townhouse" Properties(6).Address = "10116 Lottsford Drive" Properties(6).City = "Takoma Park" Properties(6).State = "MD" Properties(6).ZIPCode = 20910 Properties(6).Bedrooms = 4 Properties(6).Bathrooms = 3.5F Properties(6).MarketValue = 450500 Properties(7) = New AvailableProperty() Properties(7).PropertyNumber = 93857 Properties(7).PropertyType = "Single Family" Properties(7).Address = "9047 Woodyard Road" Properties(7).City = "York" Properties(7).State = "PA" Properties(7).ZIPCode = 17405 Properties(7).Bedrooms = 4 Properties(7).Bathrooms = 2.5F Properties(7).MarketValue = 326885 Properties(8) = New AvailableProperty() Properties(8).PropertyNumber = 930755 Properties(8).PropertyType = "Condominium" Properties(8).Address = "3842 Accolade Avenue #1206" Properties(8).City = "Alexandria" Properties(8).State = "VA" Properties(8).ZIPCode = 22231 Properties(8).Bedrooms = 3 Properties(8).Bathrooms = 2.0F Properties(8).MarketValue = 525885 Properties(9) = New AvailableProperty() Properties(9).PropertyNumber = 240875 Properties(9).PropertyType = "Townhouse" Properties(9).Address = "842 Hempton Street" Properties(9).City = "Charlestown" Properties(9).State = "WV" Properties(9).ZIPCode = 25414 Properties(9).Bedrooms = 3 Properties(9).Bathrooms = 2.5F Properties(9).MarketValue = 212500 Properties(10) = New AvailableProperty() Properties(10).PropertyNumber = 940075 Properties(10).PropertyType = "Single Family" Properties(10).Address = "4813 Woodland Court" Properties(10).City = "Falls Church" Properties(10).State = "VA" Properties(10).ZIPCode = 22042 Properties(10).Bedrooms = 5 Properties(10).Bathrooms = 3.5F Properties(10).MarketValue = 645860 Properties(11) = New AvailableProperty() Properties(11).PropertyNumber = 931475 Properties(11).PropertyType = "Townhouse" Properties(11).Address = "5030 Goodson Road" Properties(11).City = "Arlington" Properties(11).State = "VA" Properties(11).ZIPCode = 22203 Properties(11).Bedrooms = 4 Properties(11).Bathrooms = 3.5F Properties(11).MarketValue = 435775 Properties(12) = New AvailableProperty() Properties(12).PropertyNumber = 248095 Properties(12).PropertyType = "Condominium" Properties(12).Address = "9182 Weston Ave NW #F14" Properties(12).City = "Washington" Properties(12).State = "DC" Properties(12).ZIPCode = 20016 Properties(12).Bedrooms = 2 Properties(12).Bathrooms = 1.0F Properties(12).MarketValue = 425665 Properties(13) = New AvailableProperty() Properties(13).PropertyNumber = 293705 Properties(13).PropertyType = "Single Family" Properties(13).Address = "12404 Livingston Boulevard" Properties(13).City = "Martinsburg" Properties(13).State = "WV" Properties(13).ZIPCode = 25401 Properties(13).Bedrooms = 4 Properties(13).Bathrooms = 2.5F Properties(13).MarketValue = 225660 Properties(14) = New AvailableProperty() Properties(14).PropertyNumber = 937905 Properties(14).PropertyType = "Condominium" Properties(14).Address = "2039 Gonnard Road E5" Properties(14).City = "Laurel" Properties(14).State = "MD" Properties(14).ZIPCode = 20747 Properties(14).Bedrooms = 2 Properties(14).Bathrooms = 2 Properties(14).MarketValue = 275880 End Sub End Class

3. In the Class Name combo box, select btnShow
4. In the Method Name combo box, select Click and implement the event as follows:
    

   Private Sub btnShow_Click(ByVal sender As Object, _ ByVal e As System.EventArgs) _ Handles btnShow.Click lbxPropertyNumbers.Items.Clear() lbxAddresses.Items.Clear() lbxCities.Items.Clear() lbxStates.Items.Clear() lbxZIPCodes.Items.Clear() lbxBedrooms.Items.Clear() lbxBathrooms.Items.Clear() lbxMarketValues.Items.Clear() If lbxPropertiesTypes.CheckedItems.Contains("Single Families") Then For Each prop As AvailableProperty In Properties If prop.PropertyType = "Single Family" Then lbxPropertyNumbers.Items.Add(CStr(prop.PropertyNumber)) lbxAddresses.Items.Add(prop.Address) lbxCities.Items.Add(prop.City) lbxStates.Items.Add(prop.State) lbxZIPCodes.Items.Add(prop.ZIPCode) lbxBedrooms.Items.Add(prop.Bedrooms) lbxBathrooms.Items.Add(prop.Bathrooms) lbxMarketValues.Items.Add(prop.MarketValue) End If Next End If If lbxPropertiesTypes.CheckedItems.Contains("Townhouses") Then For Each prop As AvailableProperty In Properties If prop.PropertyType = "Townhouse" Then lbxPropertyNumbers.Items.Add(prop.PropertyNumber.ToString()) lbxAddresses.Items.Add(prop.Address) lbxCities.Items.Add(prop.City) lbxStates.Items.Add(prop.State) lbxZIPCodes.Items.Add(prop.ZIPCode) lbxBedrooms.Items.Add(prop.Bedrooms) lbxBathrooms.Items.Add(prop.Bathrooms) lbxMarketValues.Items.Add(prop.MarketValue) End If Next End If If lbxPropertiesTypes.CheckedItems.Contains("Condominiums") Then For Each prop As AvailableProperty In Properties If prop.PropertyType = "Condominium" Then lbxPropertyNumbers.Items.Add(prop.PropertyNumber.ToString()) lbxAddresses.Items.Add(prop.Address) lbxCities.Items.Add(prop.City) lbxStates.Items.Add(prop.State) lbxZIPCodes.Items.Add(prop.ZIPCode) lbxBedrooms.Items.Add(prop.Bedrooms) lbxBathrooms.Items.Add(prop.Bathrooms) lbxMarketValues.Items.Add(prop.MarketValue) End If Next End If End Sub

5. In the Class Name combo box, select btnClose
6. In the Method Name combo box, select Click and implement the event as follows:
    

   Private Sub btnClose_Click(ByVal sender As Object, _ ByVal e As System.EventArgs) _ Handles btnClose.Click End End Sub

7. Execute the application and test the checked list box
    
8. Close the form and return to your programming environment

From its default implementation, when a checked list box is presented to the user, when an item is clicked, its string gets highlighted but no check mark is put in the box. To put a check mark on the item, the user must click it again. This is not an anomaly. It is purposely so the user would know the difference between an item that is selected and one that is checked.

To support the ability to automatically put a check mark on an item when the user clicks it, the CheckedListBox provides the CheckOnClick Boolean property. Its default value is False. If you want the items to be automatically checked, set this property to true.

On an existing checked list box, to find out if the its items are automatically checked, get the value of the CheckOnClick property.

1. On the form, click the checked list box
2. In the Properties window, double-click CheckOnClick to set its value to True
3. To make sure that when the user selects an item in one list box, the corresponding index is selected in the other text boxes, write the following events:
    

   Private Sub lbxPropertyNumbers_SelectedIndexChanged(ByVal sender As Object, _ ByVal e As System.EventArgs) _ Handles lbxPropertyNumbers.SelectedIndexChanged lbxAddresses.SelectedIndex = lbxPropertyNumbers.SelectedIndex lbxMarketValues.SelectedIndex = lbxPropertyNumbers.SelectedIndex lbxBathrooms.SelectedIndex = lbxPropertyNumbers.SelectedIndex lbxBedrooms.SelectedIndex = lbxPropertyNumbers.SelectedIndex lbxZIPCodes.SelectedIndex = lbxPropertyNumbers.SelectedIndex lbxStates.SelectedIndex = lbxPropertyNumbers.SelectedIndex lbxCities.SelectedIndex = lbxPropertyNumbers.SelectedIndex End Sub Private Sub lbxAddresses_SelectedIndexChanged(ByVal sender As Object, _ ByVal e As System.EventArgs) _ Handles lbxAddresses.SelectedIndexChanged lbxPropertyNumbers.SelectedIndex = lbxAddresses.SelectedIndex lbxMarketValues.SelectedIndex = lbxPropertyNumbers.SelectedIndex lbxBathrooms.SelectedIndex = lbxPropertyNumbers.SelectedIndex lbxBedrooms.SelectedIndex = lbxPropertyNumbers.SelectedIndex lbxZIPCodes.SelectedIndex = lbxPropertyNumbers.SelectedIndex lbxStates.SelectedIndex = lbxPropertyNumbers.SelectedIndex lbxCities.SelectedIndex = lbxPropertyNumbers.SelectedIndex End Sub Private Sub lbxCities_SelectedIndexChanged(ByVal sender As Object, _ ByVal e As System.EventArgs) _ Handles lbxCities.SelectedIndexChanged lbxPropertyNumbers.SelectedIndex = lbxCities.SelectedIndex lbxMarketValues.SelectedIndex = lbxPropertyNumbers.SelectedIndex lbxBathrooms.SelectedIndex = lbxPropertyNumbers.SelectedIndex lbxBedrooms.SelectedIndex = lbxPropertyNumbers.SelectedIndex lbxZIPCodes.SelectedIndex = lbxPropertyNumbers.SelectedIndex lbxStates.SelectedIndex = lbxPropertyNumbers.SelectedIndex lbxAddresses.SelectedIndex = lbxPropertyNumbers.SelectedIndex End Sub Private Sub lbxStates_SelectedIndexChanged(ByVal sender As Object, _ ByVal e As System.EventArgs) _ Handles lbxStates.SelectedIndexChanged lbxPropertyNumbers.SelectedIndex = lbxStates.SelectedIndex lbxMarketValues.SelectedIndex = lbxPropertyNumbers.SelectedIndex lbxBathrooms.SelectedIndex = lbxPropertyNumbers.SelectedIndex lbxBedrooms.SelectedIndex = lbxPropertyNumbers.SelectedIndex lbxZIPCodes.SelectedIndex = lbxPropertyNumbers.SelectedIndex lbxCities.SelectedIndex = lbxPropertyNumbers.SelectedIndex lbxAddresses.SelectedIndex = lbxPropertyNumbers.SelectedIndex End Sub Private Sub lbxZIPCodes_SelectedIndexChanged(ByVal sender As Object, _ ByVal e As System.EventArgs) _ Handles lbxZIPCodes.SelectedIndexChanged lbxPropertyNumbers.SelectedIndex = lbxZIPCodes.SelectedIndex lbxMarketValues.SelectedIndex = lbxPropertyNumbers.SelectedIndex lbxBathrooms.SelectedIndex = lbxPropertyNumbers.SelectedIndex lbxBedrooms.SelectedIndex = lbxPropertyNumbers.SelectedIndex lbxStates.SelectedIndex = lbxPropertyNumbers.SelectedIndex lbxCities.SelectedIndex = lbxPropertyNumbers.SelectedIndex lbxAddresses.SelectedIndex = lbxPropertyNumbers.SelectedIndex End Sub Private Sub lbxBedrooms_SelectedIndexChanged(ByVal sender As Object, _ yVal e As System.EventArgs) _ Handles lbxBedrooms.SelectedIndexChanged lbxPropertyNumbers.SelectedIndex = lbxBedrooms.SelectedIndex lbxMarketValues.SelectedIndex = lbxPropertyNumbers.SelectedIndex lbxBathrooms.SelectedIndex = lbxPropertyNumbers.SelectedIndex lbxZIPCodes.SelectedIndex = lbxPropertyNumbers.SelectedIndex lbxStates.SelectedIndex = lbxPropertyNumbers.SelectedIndex lbxCities.SelectedIndex = lbxPropertyNumbers.SelectedIndex lbxAddresses.SelectedIndex = lbxPropertyNumbers.SelectedIndex End Sub Private Sub lbxBathrooms_SelectedIndexChanged(ByVal sender As Object, _ ByVal e As System.EventArgs) _ Handles lbxBathrooms.SelectedIndexChanged lbxPropertyNumbers.SelectedIndex = lbxBathrooms.SelectedIndex lbxMarketValues.SelectedIndex = lbxPropertyNumbers.SelectedIndex lbxBedrooms.SelectedIndex = lbxPropertyNumbers.SelectedIndex lbxZIPCodes.SelectedIndex = lbxPropertyNumbers.SelectedIndex lbxStates.SelectedIndex = lbxPropertyNumbers.SelectedIndex lbxCities.SelectedIndex = lbxPropertyNumbers.SelectedIndex lbxAddresses.SelectedIndex = lbxPropertyNumbers.SelectedIndex End Sub Private Sub lbxMarketValues_SelectedIndexChanged(ByVal sender As Object, _ ByVal e As System.EventArgs) _ Handles lbxMarketValues.SelectedIndexChanged lbxPropertyNumbers.SelectedIndex = lbxMarketValues.SelectedIndex lbxBathrooms.SelectedIndex = lbxPropertyNumbers.SelectedIndex lbxBedrooms.SelectedIndex = lbxPropertyNumbers.SelectedIndex lbxZIPCodes.SelectedIndex = lbxPropertyNumbers.SelectedIndex lbxStates.SelectedIndex = lbxPropertyNumbers.SelectedIndex lbxCities.SelectedIndex = lbxPropertyNumbers.SelectedIndex lbxAddresses.SelectedIndex = lbxPropertyNumbers.SelectedIndex End Sub

4. Save the form

After creating the list, each item appears with a flat check box to its left. If you want a 3-D check box, you can change the Boolean ThreeDCheckBoxes property from its False default to a True value:

ThreeDCheckBoxes
False	True