ComboBox Class

Represents a Windows combo box control.

Namespace: System.Windows.Forms
Assembly: System.Windows.Forms (in

<ClassInterfaceAttribute(ClassInterfaceType.AutoDispatch)> _
<ComVisibleAttribute(True)> _
Public Class ComboBox
	Inherits ListControl
Dim instance As ComboBox

/** @attribute ClassInterfaceAttribute(ClassInterfaceType.AutoDispatch) */ 
/** @attribute ComVisibleAttribute(true) */ 
public class ComboBox extends ListControl
public class ComboBox extends ListControl

A ComboBox displays a text box edit field combined with a ListBox, enabling the user to select items from the list or to enter new text. The default behavior of ComboBox displays an edit field with a hidden drop-down list. The DropDownStyle property determines the style of combo box to display. You can enter a value that provides a simple drop-down, where the list always displays, a drop-down list box, where the text portion is not editable and you must select an arrow to view the drop-down list box, or the default drop-down list box, where the text portion is editable and the user must press the arrow key to view the list. To display a list that the user cannot edit, use a ListBox control.

To add objects to the list at run time, assign an array of object references with the AddRange method. The list then displays the default string value for each object. You can add individual objects with the Add method.

In addition to display and selection functionality, the ComboBox also provides features that enable you to efficiently add items to the ComboBox and to find text within the items of the list. With the BeginUpdate and EndUpdate methods, you can add a large number of items to the ComboBox without the control being repainted each time an item is added to the list. The FindString and FindStringExact methods enable you to search for an item in the list that contains a specific search string.

You can use these properties to manage the currently selected item in the list, the Text property to specify the string displayed in the editing field, the SelectedIndex property to get or set the current item, and the SelectedItem property to get or set a reference to the object.


If you have a ListBox, ComboBox, or CheckedListBox on a base Windows Forms page and want to modify the string collections of those controls in a derived form, the string collections of those controls in the base form must be empty. If the string collections are not empty, they become read-only when you derive another form.

The following code example is a complete application showing how you can use the Add method to add items to a ComboBox, the FindString method to find items in a ComboBox, and the BeginUpdate and EndUpdate methods to efficiently add a large number items to a ComboBox.

Imports System
Imports System.Windows.Forms

Namespace ComboBoxSampleNamespace

    Public Class ComboBoxSample
        Inherits System.Windows.Forms.Form

        Private addButton As System.Windows.Forms.Button
        Private textBox2 As System.Windows.Forms.TextBox
        Private addGrandButton As System.Windows.Forms.Button
        Private comboBox1 As System.Windows.Forms.ComboBox
        Private showSelectedButton As System.Windows.Forms.Button
        Private textBox1 As System.Windows.Forms.TextBox
        Private findButton As System.Windows.Forms.Button
        Private label1 As System.Windows.Forms.Label

        Public Sub New()
        End Sub

        <System.STAThreadAttribute()> Public Shared Sub Main()
            System.Windows.Forms.Application.Run(New ComboBoxSample())
        End Sub

        Private Sub InitializeComponent()
            Me.addButton = New System.Windows.Forms.Button()
            Me.textBox2 = New System.Windows.Forms.TextBox()
            Me.addGrandButton = New System.Windows.Forms.Button()
            Me.comboBox1 = New System.Windows.Forms.ComboBox()
            Me.showSelectedButton = New System.Windows.Forms.Button()
            Me.textBox1 = New System.Windows.Forms.TextBox()
            Me.findButton = New System.Windows.Forms.Button()
            Me.label1 = New System.Windows.Forms.Label()
            Me.addButton.Location = New System.Drawing.Point(248, 32)
            Me.addButton.Size = New System.Drawing.Size(40, 24)
            Me.addButton.TabIndex = 1
            Me.addButton.Text = "Add"
            AddHandler Me.addButton.Click, AddressOf Me.addButton_Click
            Me.textBox2.Location = New System.Drawing.Point(8, 64)
            Me.textBox2.Size = New System.Drawing.Size(232, 20)
            Me.textBox2.TabIndex = 6
            Me.textBox2.Text = ""
            Me.addGrandButton.Location = New System.Drawing.Point(8, 96)
            Me.addGrandButton.Size = New System.Drawing.Size(280, 23)
            Me.addGrandButton.TabIndex = 2
            Me.addGrandButton.Text = "Add 1,000 Items"
            AddHandler Me.addGrandButton.Click, AddressOf Me.addGrandButton_Click
            Me.comboBox1.Anchor = ((System.Windows.Forms.AnchorStyles.Bottom Or System.Windows.Forms.AnchorStyles.Left) _
                        Or System.Windows.Forms.AnchorStyles.Right)
            Me.comboBox1.DropDownWidth = 280
            Me.comboBox1.Items.AddRange(New Object() {"Item 1", "Item 2", "Item 3", "Item 4", "Item 5"})
            Me.comboBox1.Location = New System.Drawing.Point(8, 248)
            Me.comboBox1.Size = New System.Drawing.Size(280, 21)
            Me.comboBox1.TabIndex = 7
            Me.showSelectedButton.Location = New System.Drawing.Point(8, 128)
            Me.showSelectedButton.Size = New System.Drawing.Size(280, 24)
            Me.showSelectedButton.TabIndex = 4
            Me.showSelectedButton.Text = "What Item is Selected?"
            AddHandler Me.showSelectedButton.Click, AddressOf Me.showSelectedButton_Click
            Me.textBox1.Location = New System.Drawing.Point(8, 32)
            Me.textBox1.Size = New System.Drawing.Size(232, 20)
            Me.textBox1.TabIndex = 5
            Me.textBox1.Text = ""
            Me.findButton.Location = New System.Drawing.Point(248, 64)
            Me.findButton.Size = New System.Drawing.Size(40, 24)
            Me.findButton.TabIndex = 3
            Me.findButton.Text = "Find"
            AddHandler Me.findButton.Click, AddressOf Me.findButton_Click
            Me.label1.Location = New System.Drawing.Point(8, 224)
            Me.label1.Size = New System.Drawing.Size(144, 23)
            Me.label1.TabIndex = 0
            Me.label1.Text = "Test ComboBox"
            Me.ClientSize = New System.Drawing.Size(292, 273)
            Me.Controls.AddRange(New System.Windows.Forms.Control() {Me.comboBox1, Me.textBox2, Me.textBox1, Me.showSelectedButton, Me.findButton, Me.addGrandButton, Me.addButton, Me.label1})
            Me.Text = "ComboBox Sample"
        End Sub

        Private Sub addButton_Click(ByVal sender As Object, ByVal e As System.EventArgs)
        End Sub

        Private Sub findButton_Click(ByVal sender As Object, ByVal e As System.EventArgs)
            Dim index As Integer
            index = comboBox1.FindString(textBox2.Text)
            comboBox1.SelectedIndex = index
        End Sub

        Private Sub addGrandButton_Click(ByVal sender As Object, ByVal e As System.EventArgs)
            Dim I As Integer
            For I = 0 To 1000
                comboBox1.Items.Add("Item 1" + i.ToString())
        End Sub

        Private Sub showSelectedButton_Click(ByVal sender As Object, ByVal e As System.EventArgs)
            Dim selectedIndex As Integer
            selectedIndex = comboBox1.SelectedIndex
            Dim selectedItem As Object
            selectedItem = comboBox1.SelectedItem

            MessageBox.Show("Selected Item Text: " & selectedItem.ToString() & Microsoft.VisualBasic.Constants.vbCrLf & _
                                "Index: " & selectedIndex.ToString())
        End Sub
    End Class
End Namespace

package Win32Form1Namespace;

import System.*;
import System.Windows.Forms.*;

public class Win32Form1 extends System.Windows.Forms.Form
    private System.Windows.Forms.Button addButton;
    private System.Windows.Forms.TextBox textBox2;
    private System.Windows.Forms.Button addGrandButton;
    private System.Windows.Forms.ComboBox comboBox1;
    private System.Windows.Forms.Button showSelectedButton;
    private System.Windows.Forms.TextBox textBox1;
    private System.Windows.Forms.Button findButton;
    private System.Windows.Forms.Label label1;

    public Win32Form1()
    } //Win32Form1

    /** @attribute System.STAThreadAttribute()
    public static void main(String[] args)
        System.Windows.Forms.Application.Run(new Win32Form1());
    } //main
    private void InitializeComponent()
        this.addButton = new System.Windows.Forms.Button();
        this.textBox2 = new System.Windows.Forms.TextBox();
        this.addGrandButton = new System.Windows.Forms.Button();
        this.comboBox1 = new System.Windows.Forms.ComboBox();
        this.showSelectedButton = new System.Windows.Forms.Button();
        this.textBox1 = new System.Windows.Forms.TextBox();
        this.findButton = new System.Windows.Forms.Button();
        this.label1 = new System.Windows.Forms.Label();
        this.addButton.set_Location(new System.Drawing.Point(248, 32));
        this.addButton.set_Size(new System.Drawing.Size(40, 24));
        this.addButton.add_Click(new System.EventHandler(this.addButton_Click));
        this.textBox2.set_Location(new System.Drawing.Point(8, 64));
        this.textBox2.set_Size(new System.Drawing.Size(232, 20));
        this.addGrandButton.set_Location(new System.Drawing.Point(8, 96));
        this.addGrandButton.set_Size(new System.Drawing.Size(280, 23));
        this.addGrandButton.set_Text("Add 1,000 Items");
        this.addGrandButton.add_Click(new System.EventHandler(
            | System.Windows.Forms.AnchorStyles.Left
            | System.Windows.Forms.AnchorStyles.Right);
        this.comboBox1.get_Items().AddRange(new Object[] 
            { "Item 1", "Item 2", "Item 3", "Item 4", "Item 5" });
        this.comboBox1.set_Location(new System.Drawing.Point(8, 248));
        this.comboBox1.set_Size(new System.Drawing.Size(280, 21));
        this.showSelectedButton.set_Location(new System.Drawing.Point(8, 128));
        this.showSelectedButton.set_Size(new System.Drawing.Size(280, 24));
        this.showSelectedButton.set_Text("What Item is Selected?");
        this.showSelectedButton.add_Click(new System.EventHandler(
        this.textBox1.set_Location(new System.Drawing.Point(8, 32));
        this.textBox1.set_Size(new System.Drawing.Size(232, 20));
        this.findButton.set_Location(new System.Drawing.Point(248, 64));
        this.findButton.set_Size(new System.Drawing.Size(40, 24));
        this.findButton.add_Click(new System.EventHandler(
        this.label1.set_Location(new System.Drawing.Point(8, 224));
        this.label1.set_Size(new System.Drawing.Size(144, 23));
        this.label1.set_Text("Test ComboBox");
        this.set_ClientSize(new System.Drawing.Size(292, 273));
        this.get_Controls().AddRange(new System.Windows.Forms.Control[]
            { this.comboBox1, this.textBox2, this.textBox1,
            this.showSelectedButton, this.findButton, this.addGrandButton,
            this.addButton, this.label1 });
        this.set_Text("ComboBox Sample");
    } //InitializeComponent

    private void addButton_Click(Object sender, System.EventArgs e)
    } //addButton_Click

    private void addGrandButton_Click(Object sender, System.EventArgs e)
        for (int i = 0; i < 1000; i++) {
            comboBox1.get_Items().Add("Item 1" + ((Int32)i).ToString());
    } //addGrandButton_Click

    private void findButton_Click(Object sender, System.EventArgs e)
        int index = comboBox1.FindString(textBox2.get_Text());
    } //findButton_Click

    private void showSelectedButton_Click(Object sender, System.EventArgs e)
        int selectedIndex = comboBox1.get_SelectedIndex();
        Object selectedItem = comboBox1.get_SelectedItem();
        MessageBox.Show("Selected Item Text: " + selectedItem.ToString() 
            + "\n" + "Index: " + ((Int32)selectedIndex).ToString());
    } //showSelectedButton_Click

Any public static (Shared in Visual Basic) members of this type are thread safe. Any instance members are not guaranteed to be thread safe.

Windows 98, Windows 2000 SP4, Windows CE, Windows Millennium Edition, Windows Mobile for Pocket PC, Windows Mobile for Smartphone, Windows Server 2003, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP SP2, Windows XP Starter Edition

The .NET Framework does not support all versions of every platform. For a list of the supported versions, see System Requirements.

.NET Framework

Supported in: 2.0, 1.1, 1.0

.NET Compact Framework

Supported in: 2.0, 1.0