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ListBox.SelectedIndexChanged Event

Occurs when the SelectedIndex property or the SelectedIndices collection 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 ListBox has been changed. This can be useful when you need to display information in other controls based on the current selection in the ListBox. You can use the event handler for this event to load the information in the other controls.

If the SelectionMode property is set to SelectionMode.MultiSimple or SelectionMode.MultiExtended, any change to the SelectedIndices collection, including removing an item from the selection, will raise this event.

For more information about handling events, see Consuming Events.

The following code example demonstrates how to use the SelectedIndexChanged event to search for and select an item in a different ListBox control. The example uses the SelectedIndexChanged event to determine when the selected item in the ListBox is changed. The example code then reads the text of the item using the SelectedItem property and calls the FindString method on a different ListBox using the text returned by SelectedItem in the first ListBox. If an item is found in the other ListBox, the item is selected. This example requires that two ListBox controls, named listBox1 and listBox2, have been added to a form and that both ListBox controls contain items that are identical. The example also requires that the event-handling method defined in the example is connected to the SelectedIndexChanged event of listBox1.

private void listBox1_SelectedIndexChanged(object sender, System.EventArgs e)
   // Get the currently selected item in the ListBox.
   string curItem = listBox1.SelectedItem.ToString();

   // Find the string in ListBox2.
   int index = listBox2.FindString(curItem);
   // If the item was not found in ListBox 2 display a message box, otherwise select it in ListBox2.
   if(index == -1)
      MessageBox.Show("Item is not available in ListBox2");

.NET Framework

Supported in: 4, 3.5, 3.0, 2.0, 1.1, 1.0

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

Windows 7, Windows Vista SP1 or later, Windows XP SP3, Windows XP SP2 x64 Edition, Windows Server 2008 (Server Core not supported), Windows Server 2008 R2 (Server Core supported with SP1 or later), Windows Server 2003 SP2

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