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combobox-control-overview-windows-forms.md

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title description ms.date f1_keywords helpviewer_keywords ms.assetid
ComboBox Control Overview
Learn about a the ComboBox control in Windows Forms, which is used to display data in a drop-down combo box.
03/30/2017
ComboBox
drop-down lists [Windows Forms], Windows Forms
ComboBox control [Windows Forms], about ComboBox control
drop-down lists [Windows Forms], ComboBox control
combo boxes [Windows Forms], about combo boxes
a58b393f-a614-45d1-8961-857a024b5acd

ComboBox Control Overview (Windows Forms)

The Windows Forms xref:System.Windows.Forms.ComboBox control is used to display data in a drop-down combo box. By default, the xref:System.Windows.Forms.ComboBox control appears in two parts: the top part is a text box that allows the user to type a list item. The second part is a list box that displays a list of items from which the user can select one. For more information on other styles of combo box, see When to Use a Windows Forms ComboBox Instead of a ListBox.

The xref:System.Windows.Forms.ComboBox.SelectedIndex%2A property returns an integer value that corresponds to the selected list item. You can programmatically change the selected item by changing the xref:System.Windows.Forms.ComboBox.SelectedIndex%2A value in code; the corresponding item in the list will appear in the text box portion of the combo box. If no item is selected, the xref:System.Windows.Forms.ComboBox.SelectedIndex%2A value is -1. If the first item in the list is selected, then the xref:System.Windows.Forms.ComboBox.SelectedIndex%2A value is 0. The xref:System.Windows.Forms.ComboBox.SelectedItem%2A property is similar to xref:System.Windows.Forms.ComboBox.SelectedIndex%2A , but returns the item itself, usually a string value. The xref:System.Windows.Forms.ComboBox.ObjectCollection.Count%2A property reflects the number of items in the list, and the value of the xref:System.Windows.Forms.ComboBox.ObjectCollection.Count%2A property is always one more than the largest possible xref:System.Windows.Forms.ComboBox.SelectedIndex%2A value because xref:System.Windows.Forms.ComboBox.SelectedIndex%2A is zero-based.

To add or delete items in a xref:System.Windows.Forms.ComboBox control, use the xref:System.Windows.Forms.ComboBox.ObjectCollection.Add%2A, xref:System.Windows.Forms.ComboBox.ObjectCollection.Insert%2A, xref:System.Windows.Forms.ComboBox.ObjectCollection.Clear%2A or xref:System.Windows.Forms.ComboBox.ObjectCollection.Remove%2A method. Alternatively, you can add items to the list by using the xref:System.Windows.Forms.ComboBox.Items%2A property in the designer.

See also