Introduction

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 class Exercise : System.Windows.Forms.Form
{
    CheckedListBox lbxPersonalRelationships;

    public Exercise()
    {
        InitializeComponent();
    }

    private void 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);
    }
}

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. Its formula is:

private void lbxPropertiesTypes_ItemCheck(object sender, ItemCheckEventArgs e)
{

}

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 bool Contains(object item);

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:
    

   using System; using System.Collections.Generic; using System.ComponentModel; using System.Data; using System.Drawing; using System.Text; using System.Windows.Forms; namespace AltairRealtors1 { public partial class RealEstate : Form { AvailableProperty[] properties = new AvailableProperty[15]; public RealEstate() { InitializeComponent(); } private void RealEstate_Load(object sender, EventArgs e) { 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 = 2.50F; 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; } } }

3. Return to the form
4. On the form, double-click the Show button and implement its Click event as follows:
    

   private void btnShow_Click(object sender, EventArgs e) { 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")) { foreach (AvailableProperty prop in properties) { if (prop.PropertyType == "Single Family") { 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); } } } if (lbxPropertiesTypes.CheckedItems.Contains("Townhouses")) { foreach (AvailableProperty prop in properties) { if (prop.PropertyType == "Townhouse") { 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); } } } if (lbxPropertiesTypes.CheckedItems.Contains("Condominiums")) { foreach (AvailableProperty prop in properties) { if (prop.PropertyType == "Condominium") { 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); } } } }

5. Return to the form and double-click the Close button
6. Implement its event as follows:
    

   private void btnClose_Click(object sender, EventArgs e) { Close(); }

7. Execute the application and test the checked list box
    
8. Close the form and return to your programming environment
9. To make sure that when a user clicks an item in one list box, the corresponding item gets selected in the other list boxes, on the form, click the Prop # list box
10. Press and hold Shift
11. Click each of the other list boxes
12. Release Shift
13. In the Properties window, click the Events button and double-click SelectedIndexChanged
14. Implement the event as follows:
     

    private void lbxPropertyNumbers_SelectedIndexChanged(object sender, EventArgs e) { lbxMarketValues.SelectedIndex = lbxBathrooms.SelectedIndex = lbxBedrooms.SelectedIndex = lbxZIPCodes.SelectedIndex = lbxStates.SelectedIndex = lbxCities.SelectedIndex = lbxAddresses.SelectedIndex = lbxPropertyNumbers.SelectedIndex; }

15. Return to the form

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. 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