Home > Articles > Programming > Windows Programming

  • Print
  • + Share This
This chapter is from the book

7.4 ListBox, CheckedListBox, and ComboBox Classes

The ListBox Class

The ListBox control is used to provide a list of items from which the user may select one or more items. This list is typically text but can also include images and objects. Other features of the ListBox include methods to perform text-based searches, sorting, multi-column display, horizontal and vertical scroll bars, and an easy way to override the default appearance and create owner-drawn ListBox items.

constructor: public ListBox()

The constructor creates an empty ListBox. The code to populate a ListBox is typically placed in the containing form’s constructor or Form.Load event handler. If the ListBox.Sorted property is set to true, ListBox items are sorted alphabetically in ascending order. Also, vertical scroll bars are added automatically if the control is not long enough to display all items.

Adding Items to a ListBox

A ListBox has an Items collection that contains all elements of the list. Elements can be added by binding the ListBox to a data source (described in Chapter 11, "ADO.NET") or manually by using the Add method. If the Sorted property is false, the items are listed in the order they are entered. There is also an Insert method that places an item at a specified location.

lstArtists.Items.Add("Monet");
lstArtists.Items.Add("Rembrandt");
lstArtists.Items.Add("Manet");
lstArtists.Items.Insert(0, "Botticelli"); //Place at top 

List boxes may also contain objects. Because an object may have many members, this raises the question of what is displayed in the TextBox list. Because by default a ListBox displays the results of an item’s ToString method, it is necessary to override this System.Object method to return the string you want displayed. The following class is used to create ListBox items:

// Instances of this class will be placed in a ListBox
public class Artist
{
  public string BDate, DDate, Country;
  private string firstname;
  private string lastname;
  public Artist(string birth, string death, string fname,
         string lname, string ctry)
  {
   BDate = birth;
   DDate = death;
   Country = ctry;
   firstname = fname;
   lastname = lname;
  }
  public override string ToString() {
   return (lastname+" , "+firstname);
  }
  public string GetLName  {
   get{ return lastname;} 
  }
  public string GetFName  {
   get{ return firstname;} 
  }
}

ToString has been overridden to return the artist’s last and first names, which are displayed in the ListBox. The ListBox (Figure 7-9) is populated using these statements:

lstArtists.Items.Add
  (new Artist("1832", "1883", "Edouard", "Manet","Fr" ));
lstArtists.Items.Add
  (new Artist("1840", "1926", "Claude", "Monet","Fr"));
lstArtists.Items.Add
  (new Artist("1606", "1669", "Von Rijn", "Rembrandt","Ne"));
lstArtists.Items.Add
(new Artist("1445", "1510", "Sandre", "Botticelli","It"));
Figure 7-9

Figure 7-9 ListBox items: (A) Default and (B) Custom drawn

Selecting and Searching for Items in a ListBox

The SelectionMode property determines the number of items a ListBox allows to be selected at one time. It takes four values from the SelectionMode enumeration: None, Single, MultiSingle, and MultiExtended. MultiSingle allows selection by clicking an item or pressing the space bar; MultiExtended permits the use of the Shift and Ctrl keys.

The SelectedIndexChanged event provides an easy way to detect when an item in a ListBox is selected. It is fired when the user clicks on an item or uses the arrow keys to traverse a list. A common use is to display further information about the selection in other controls on the form. Here is code that displays an artist’s dates of birth and death when the artist’s name is selected from the ListBox in Figure 7-9:

// Set up event handler in constructor
lstArtists.SelectedIndexChanged += new EventHandler(ShowArtist);
//
private void ShowArtist(object sender, EventArgs e)
{
  // Cast to artist object in order to access properties
  Artist myArtist = lstArtists.SelectedItem as Artist;
  if (myArtist != null) {
   txtBirth.Text = myArtist.Dob; // Place dates in text boxes
   txtDeath.Text = myArtist.Dod;
  }
}

The SelectedItem property returns the item selected in the ListBox. This object is assigned to myArtist using the as operator, which ensures the object is an Artist type. The SelectedIndex property can also be used to reference the selected item:

myArtist = lstArtists.Items[lstArtists.SelectedIndex] as Artist;

Working with a multi-selection ListBox requires a different approach. You typically do not want to respond to a selection event until all items have been selected. One approach is to have the user click a button to signal that all choices have been made and the next action is required. All selections are exposed as part of the SelectedItems collection, so it is an easy matter to enumerate the items:

foreach (Artist a in lstArtists.SelectedItems)
  MessageBox.Show(a.GetLName);

The SetSelected method provides a way to programatically select an item or items in a ListBox. It highlights the item(s) and fires the SelectedIndexChanged event. In this example, SetSelected is used to highlight all artists who were born in France:

lstArtists.ClearSelected();  // Clear selected items
for (int ndx =0; ndx < lstArtists.Items.Count-1; ndx ++)
{
  Artist a = lstArtists.Items[ndx] as Artist;
  if (a.country == "Fr") lstArtists.SetSelected(ndx,true);
}

Customizing the Appearance of a ListBox

The ListBox, along with the ComboBox, MenuItem, and TabControl controls, is an owner-drawn control. This means that by setting a control property, you can have it fire an event when the control’s contents need to be drawn. A custom event handler takes care of the actual drawing.

To enable owner drawing of the ListBox, the DrawMode property must be set to one of two DrawMode enumeration values: OwnerDrawFixed or OwnerDrawVariable. The former draws each item a fixed size; the latter permits variable-sized items. Both of these cause the DrawItem event to be fired and rely on its event handler to perform the drawing.

Using the ListBox from the previous example, we can use the constructor to set DrawMode and register an event handler for the DrawItem event:

lstArtists.DrawMode = DrawMode.OwnerDrawFixed;
lstArtists.ItemHeight = 16; // Height (pixels) of item
lstArtists.DrawItem += new DrawItemEventHandler(DrawList);

The DrawItemEventHandler delegate has two parameters: the familiar sender object and the DrawItemEventArgs object. The latter is of more interest. It contains properties related to the control’s appearance and state as well as a couple of useful drawing methods. Table 7-2 summarizes these.

Table 7-2 DrawItemEventArgs Properties

Member

Description

BackColor

Background color assigned to the control.

Bounds

Defines the coordinates of the item to be drawn as a Rectangle object.

Font

Returns the font assigned to the item being drawn.

ForeColor

Foreground color of the control. This is the color of the text displayed.

Graphics

Represents the surface (as a Graphics object) on which the drawing occurs.

Index

The index in the control where the item is being drawn.

State

The state of the item being drawn. This value is a DrawItemState enumeration. For a ListBox, its value is Selected (1) or None(0).

DrawBackground()

Draws the default background.

DrawFocusRectangle()

Draws the focus rectangle around the item if it has focus.

Index is used to locate the item. Font, BackColor, and ForeColor return the current preferences for each. Bounds defines the rectangular area circumscribing the item and is used to indicate where drawing should occur. State is useful for making drawing decisions based on whether the item is selected. This is particularly useful when the ListBox supports multiple selections. We looked at the Graphics object briefly in the last chapter when demonstrating how to draw on a form. Here, it is used to draw in the Bounds area. Finally, the two methods, DrawBackground and DrawFocusRectangle, are used as their name implies.

The event handler to draw items in the ListBox is shown in Listing 7-3. Its behavior is determined by the operation being performed: If an item has been selected, a black border is drawn in the background to highlight the selection; if an item is added, the background is filled with a color corresponding to the artist’s country, and the first and last names of the artist are displayed.

The routine does require knowledge of some GDI+ concepts (see Chapter 8, ".NET Graphics Using GDI+"). However, the purpose of the methods should be clear from their name and context: FillRectangle fills a rectangular area defined by the Rectangle object, and DrawString draws text to the Graphics object using a font color defined by the Brush object. Figure 7-9(B) shows the output.

Listing 7-3 Event Handler to Draw Items in a ListBox

private void DrawList(object sender, DrawItemEventArgs e)
{
  // Draw ListBox Items
  string ctry;
  Rectangle rect = e.Bounds;
  Artist a = lstArtists.Items[e.Index] as Artist;
  string artistName = a.ToString();
  if ( (e.State & DrawItemState.Selected) == 
          DrawItemState.Selected )
  {
   // Draw Black border around the selected item
   e.Graphics.DrawRectangle(Pens.Black,rect); 
  } else {
   ctry = a.Country;
   Brush b;  // Object used to define backcolor
   // Each country will have a different backcolor
   b = Brushes.LightYellow;   // Netherlands
   if (ctry == "Fr") b = Brushes.LightGreen;
   if (ctry == "It") b = Brushes.Yellow;
   e.Graphics.FillRectangle(b,rect);}
   e.Graphics.DrawString(artistName,e.Font,
              Brushes.Black,rect);
  }
}

Other List Controls: the ComboBox and the CheckedListBox

The ComboBox control is a hybrid control combining a ListBox with a TextBox (see Figure 7-10). Like the ListBox, it derives from the ListControl and thus possesses most of the same properties.

Figure 7-10

Figure 7-10 ComboBox and CheckedListBox controls are variations on ListBox

Visually, the ComboBox control consists of a text box whose contents are available through its Text property and a drop-down list from which a selected item is available through the SelectedItem property. When an item is selected, its textual representation is displayed in the text box window. A ComboBox can be useful in constructing questionnaires where the user selects an item from the drop-down list or, optionally, types in his own answer. Its construction is similar to the ListBox:

ComboBox cbArtists = new ComboBox();
cbArtists.Size = new System.Drawing.Size(120, 21);
cbArtists.MaxDropDownItems= 4; // Max number of items to display
cbArtists.DropDownWidth = 140; // Width of drop-down portion
cbArtists.Items.Add(new Artist("1832", "1883",
                "Edouard", "Manet","Fr" ));
// Add other items here...

The CheckedListBox is a variation on the ListBox control that adds a check box to each item in the list. The default behavior of the control is to select an item on the first click, and check or uncheck it on the second click. To toggle the check on and off with a single click, set the CheckOnClick property to true.

Although it does not support multiple selections, the CheckedListBox does allow multiple items to be checked and includes them in a CheckedItems collection. The code here loops through a collection of Artist objects that have been checked on the control:

// List all items with checked box.
foreach (Artist a in clBox.CheckedItems)
  MessageBox.Show(a.ToString()); //  –> Monet, Claude

You can also iterate through the collection and explicitly determine the checked state:

For (int i=0; I< clBox.Items.Count; i++)
{
  if(clBox.GetItemCheckState(i) == CheckState.Checked) 
  { Do something } else {do something if not checked }
}
  • + Share This
  • 🔖 Save To Your Account

InformIT Promotional Mailings & Special Offers

I would like to receive exclusive offers and hear about products from InformIT and its family of brands. I can unsubscribe at any time.

Overview


Pearson Education, Inc., 221 River Street, Hoboken, New Jersey 07030, (Pearson) presents this site to provide information about products and services that can be purchased through this site.

This privacy notice provides an overview of our commitment to privacy and describes how we collect, protect, use and share personal information collected through this site. Please note that other Pearson websites and online products and services have their own separate privacy policies.

Collection and Use of Information


To conduct business and deliver products and services, Pearson collects and uses personal information in several ways in connection with this site, including:

Questions and Inquiries

For inquiries and questions, we collect the inquiry or question, together with name, contact details (email address, phone number and mailing address) and any other additional information voluntarily submitted to us through a Contact Us form or an email. We use this information to address the inquiry and respond to the question.

Online Store

For orders and purchases placed through our online store on this site, we collect order details, name, institution name and address (if applicable), email address, phone number, shipping and billing addresses, credit/debit card information, shipping options and any instructions. We use this information to complete transactions, fulfill orders, communicate with individuals placing orders or visiting the online store, and for related purposes.

Surveys

Pearson may offer opportunities to provide feedback or participate in surveys, including surveys evaluating Pearson products, services or sites. Participation is voluntary. Pearson collects information requested in the survey questions and uses the information to evaluate, support, maintain and improve products, services or sites, develop new products and services, conduct educational research and for other purposes specified in the survey.

Contests and Drawings

Occasionally, we may sponsor a contest or drawing. Participation is optional. Pearson collects name, contact information and other information specified on the entry form for the contest or drawing to conduct the contest or drawing. Pearson may collect additional personal information from the winners of a contest or drawing in order to award the prize and for tax reporting purposes, as required by law.

Newsletters

If you have elected to receive email newsletters or promotional mailings and special offers but want to unsubscribe, simply email information@informit.com.

Service Announcements

On rare occasions it is necessary to send out a strictly service related announcement. For instance, if our service is temporarily suspended for maintenance we might send users an email. Generally, users may not opt-out of these communications, though they can deactivate their account information. However, these communications are not promotional in nature.

Customer Service

We communicate with users on a regular basis to provide requested services and in regard to issues relating to their account we reply via email or phone in accordance with the users' wishes when a user submits their information through our Contact Us form.

Other Collection and Use of Information


Application and System Logs

Pearson automatically collects log data to help ensure the delivery, availability and security of this site. Log data may include technical information about how a user or visitor connected to this site, such as browser type, type of computer/device, operating system, internet service provider and IP address. We use this information for support purposes and to monitor the health of the site, identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents and appropriately scale computing resources.

Web Analytics

Pearson may use third party web trend analytical services, including Google Analytics, to collect visitor information, such as IP addresses, browser types, referring pages, pages visited and time spent on a particular site. While these analytical services collect and report information on an anonymous basis, they may use cookies to gather web trend information. The information gathered may enable Pearson (but not the third party web trend services) to link information with application and system log data. Pearson uses this information for system administration and to identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents, appropriately scale computing resources and otherwise support and deliver this site and its services.

Cookies and Related Technologies

This site uses cookies and similar technologies to personalize content, measure traffic patterns, control security, track use and access of information on this site, and provide interest-based messages and advertising. Users can manage and block the use of cookies through their browser. Disabling or blocking certain cookies may limit the functionality of this site.

Do Not Track

This site currently does not respond to Do Not Track signals.

Security


Pearson uses appropriate physical, administrative and technical security measures to protect personal information from unauthorized access, use and disclosure.

Children


This site is not directed to children under the age of 13.

Marketing


Pearson may send or direct marketing communications to users, provided that

  • Pearson will not use personal information collected or processed as a K-12 school service provider for the purpose of directed or targeted advertising.
  • Such marketing is consistent with applicable law and Pearson's legal obligations.
  • Pearson will not knowingly direct or send marketing communications to an individual who has expressed a preference not to receive marketing.
  • Where required by applicable law, express or implied consent to marketing exists and has not been withdrawn.

Pearson may provide personal information to a third party service provider on a restricted basis to provide marketing solely on behalf of Pearson or an affiliate or customer for whom Pearson is a service provider. Marketing preferences may be changed at any time.

Correcting/Updating Personal Information


If a user's personally identifiable information changes (such as your postal address or email address), we provide a way to correct or update that user's personal data provided to us. This can be done on the Account page. If a user no longer desires our service and desires to delete his or her account, please contact us at customer-service@informit.com and we will process the deletion of a user's account.

Choice/Opt-out


Users can always make an informed choice as to whether they should proceed with certain services offered by InformIT. If you choose to remove yourself from our mailing list(s) simply visit the following page and uncheck any communication you no longer want to receive: www.informit.com/u.aspx.

Sale of Personal Information


Pearson does not rent or sell personal information in exchange for any payment of money.

While Pearson does not sell personal information, as defined in Nevada law, Nevada residents may email a request for no sale of their personal information to NevadaDesignatedRequest@pearson.com.

Supplemental Privacy Statement for California Residents


California residents should read our Supplemental privacy statement for California residents in conjunction with this Privacy Notice. The Supplemental privacy statement for California residents explains Pearson's commitment to comply with California law and applies to personal information of California residents collected in connection with this site and the Services.

Sharing and Disclosure


Pearson may disclose personal information, as follows:

  • As required by law.
  • With the consent of the individual (or their parent, if the individual is a minor)
  • In response to a subpoena, court order or legal process, to the extent permitted or required by law
  • To protect the security and safety of individuals, data, assets and systems, consistent with applicable law
  • In connection the sale, joint venture or other transfer of some or all of its company or assets, subject to the provisions of this Privacy Notice
  • To investigate or address actual or suspected fraud or other illegal activities
  • To exercise its legal rights, including enforcement of the Terms of Use for this site or another contract
  • To affiliated Pearson companies and other companies and organizations who perform work for Pearson and are obligated to protect the privacy of personal information consistent with this Privacy Notice
  • To a school, organization, company or government agency, where Pearson collects or processes the personal information in a school setting or on behalf of such organization, company or government agency.

Links


This web site contains links to other sites. Please be aware that we are not responsible for the privacy practices of such other sites. We encourage our users to be aware when they leave our site and to read the privacy statements of each and every web site that collects Personal Information. This privacy statement applies solely to information collected by this web site.

Requests and Contact


Please contact us about this Privacy Notice or if you have any requests or questions relating to the privacy of your personal information.

Changes to this Privacy Notice


We may revise this Privacy Notice through an updated posting. We will identify the effective date of the revision in the posting. Often, updates are made to provide greater clarity or to comply with changes in regulatory requirements. If the updates involve material changes to the collection, protection, use or disclosure of Personal Information, Pearson will provide notice of the change through a conspicuous notice on this site or other appropriate way. Continued use of the site after the effective date of a posted revision evidences acceptance. Please contact us if you have questions or concerns about the Privacy Notice or any objection to any revisions.

Last Update: November 17, 2020