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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
/** @event */
public void add_SelectedIndexChanged (EventHandler value)

/** @event */
public void remove_SelectedIndexChanged (EventHandler value)

JScript supports the use of events, but not the declaration of new ones.

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 Consuming 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. To run the example, paste the following code in a form that contains a TextBox named TextBox1 and call the InitializeComboBox method in the form's constructor or Load event.

	// 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."};

		ComboBox1.Items.AddRange(employees);
		this.ComboBox1.Location = new System.Drawing.Point(136, 32);
		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;
		this.Controls.Add(this.ComboBox1);
		
		// 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)
		{
			ComboBox1.Items.RemoveAt(resultIndex);
			count += 1;
			resultIndex = ComboBox1.FindStringExact(selectedEmployee, 
				resultIndex);
		}
		// Update the text in Textbox1.
		TextBox1.Text = TextBox1.Text+ "\r\n" + selectedEmployee + ": "
			+ count;
	}

    // Declare comboBox1 as a ComboBox.
    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." };

        comboBox1.get_Items().AddRange(employees);
        this.comboBox1.set_Location(new System.Drawing.Point(136, 32));
        this.comboBox1.set_MaxDropDownItems(5);
        this.comboBox1.set_DropDownStyle(ComboBoxStyle.DropDownList);
        this.comboBox1.set_Name("comboBox1");
        this.comboBox1.set_Size(new System.Drawing.Size(136, 81));
        this.comboBox1.set_TabIndex(0);
        this.get_Controls().Add(this.comboBox1);
        // Associate the event-handling method with the 
        // SelectedIndexChanged event.
        this.comboBox1.add_SelectedIndexChanged(new System.EventHandler(
            comboBox1_SelectedIndexChanged));
    } //InitializeComboBox
...    // 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.get_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) {
            comboBox1.get_Items().RemoveAt(resultIndex);
            count += 1;
            resultIndex = comboBox1.FindStringExact(selectedEmployee, 
                resultIndex);
        }
        // Update the text in textBox1.
        textBox1.set_Text(textBox1.get_Text() + "\r\n" + selectedEmployee 
            + ": " + count);
    } //comboBox1_SelectedIndexChanged

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
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