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ComboBox.SelectedIndexChanged Event

Occurs when the SelectedIndex property has changed.

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

public event EventHandler SelectedIndexChanged

You can create an event handler for this event to determine when the selected index in the ComboBox has been changed. This can be useful when you need to display information in other controls based on the current selection in the ComboBox. You can use the event handler for this event to load the information in the other controls.

For more information about handling events, see Handling and Raising Events.

The following code example demonstrates how to initialize a ComboBox control by setting the MaxDropDownItems and DropDownStyle properties and using the FindStringExact methods to search the ComboBox. It also shows handling the SelectedIndexChanged event.

using System.Windows.Forms;

public class Form1:

	public Form1() : base()
		this.Label1 = new System.Windows.Forms.Label();
		this.Label1.Location = new System.Drawing.Point(8, 24);
		this.Label1.Name = "Label1";
		this.Label1.Size = new System.Drawing.Size(120, 32);
		this.Label1.TabIndex = 1;
		this.Label1.Text = "Use drop-down to choose a name:";
		this.Label1.TextAlign = System.Drawing.ContentAlignment.MiddleRight;
		this.ClientSize = new System.Drawing.Size(292, 266);
		this.Name = "Form1";
		this.Text = "Form1";

	public static void Main()
		Application.Run(new Form1());

	internal System.Windows.Forms.Label Label1;

	// Declare and initialize the text box. 
	// This text box text will be update programmatically. The user is not  
	// allowed to update it, so the ReadOnly property is set to true. 
	internal System.Windows.Forms.TextBox TextBox1;

	private void InitializeTextBox()
		this.TextBox1 = new System.Windows.Forms.TextBox();
		this.TextBox1.ScrollBars = ScrollBars.Vertical;
		this.TextBox1.Location = new System.Drawing.Point(64, 128);
		this.TextBox1.Multiline = true;
		this.TextBox1.Name = "TextBox1";
		this.TextBox1.ReadOnly = true;
		this.TextBox1.Size = new System.Drawing.Size(184, 120);
		this.TextBox1.TabIndex = 4;
		this.TextBox1.Text = "Employee and Number of Awards:";

	// Declare comboBox1 as a ComboBox. 
	internal System.Windows.Forms.ComboBox ComboBox1;

	// This method initializes the combo box, adding a large string array 
	// but limiting the drop-down size to six rows so the combo box doesn't  
	// cover other controls when it expands. 
	private void InitializeComboBox()
		this.ComboBox1 = new System.Windows.Forms.ComboBox();
		string[] employees = new string[]{"Hamilton, David", "Hensien, Kari",
				"Hammond, Maria", "Harris, Keith", "Henshaw, Jeff D.", 
				"Hanson, Mark", "Harnpadoungsataya, Sariya", 
				"Harrington, Mark", "Harris, Keith", "Hartwig, Doris", 
				"Harui, Roger", "Hassall, Mark", "Hasselberg, Jonas", 
				"Harnpadoungsataya, Sariya", "Henshaw, Jeff D.", 
				"Henshaw, Jeff D.", "Hensien, Kari", "Harris, Keith", 
				"Henshaw, Jeff D.", "Hensien, Kari", "Hasselberg, Jonas",
				"Harrington, Mark", "Hedlund, Magnus", "Hay, Jeff", 
				"Heidepriem, Brandon D."};

		this.ComboBox1.Location = new System.Drawing.Point(136, 32);
        this.ComboBox1.IntegralHeight = false;
        this.ComboBox1.MaxDropDownItems = 5;
		this.ComboBox1.DropDownStyle = ComboBoxStyle.DropDownList;
		this.ComboBox1.Name = "ComboBox1";
		this.ComboBox1.Size = new System.Drawing.Size(136, 81);
		this.ComboBox1.TabIndex = 0;
		// Associate the event-handling method with the  
		// SelectedIndexChanged event. 
		this.ComboBox1.SelectedIndexChanged += 
			new System.EventHandler(ComboBox1_SelectedIndexChanged);

	// This method is called when the user changes his or her selection. 
	// It searches for all occurrences of the selected employee's 
	// name in the Items array and adds the employee's name and  
	// the number of occurrences to TextBox1.Text. 

	// CAUTION   This code exposes a known bug: If the index passed to the  
	// FindStringExact(searchString, index) method is the last index  
	// of the array, the code throws an exception. 
	private void ComboBox1_SelectedIndexChanged(object sender, 
		System.EventArgs e)

		ComboBox comboBox = (ComboBox) sender;

		// Save the selected employee's name, because we will remove 
		// the employee's name from the list. 
		string selectedEmployee = (string) ComboBox1.SelectedItem;

		int count = 0;
		int resultIndex = -1;

		// Call the FindStringExact method to find the first  
		// occurrence in the list.
		resultIndex = ComboBox1.FindStringExact(selectedEmployee);

		// Remove the name as it is found, and increment the found count.  
		// Then call the FindStringExact method again, passing in the  
		// index of the current found item so the search starts there  
		// instead of at the beginning of the list. 
		while (resultIndex!=-1)
			count += 1;
			resultIndex = ComboBox1.FindStringExact(selectedEmployee, 
		// Update the text in Textbox1.
		TextBox1.Text = TextBox1.Text+ "\r\n" + selectedEmployee + ": "
			+ count;


.NET Framework

Supported in: 4.5.2, 4.5.1, 4.5, 4, 3.5, 3.0, 2.0, 1.1, 1.0

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

Windows 8.1, Windows Server 2012 R2, Windows 8, Windows Server 2012, Windows 7, Windows Vista SP2, Windows Server 2008 (Server Core Role not supported), Windows Server 2008 R2 (Server Core Role supported with SP1 or later; Itanium not supported)

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

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