Question

I have this code behind a winforms which simply has a listbox as its only control:

Imports System.Windows.Forms
Public Class Form1

    Public Sub New()

        ' This call is required by the designer.
        InitializeComponent()

        ' Add any initialization after the InitializeComponent() call.
        ListBoxX.Items.Add("hello")
        ListBoxX.Items.Add("world")
        ListBoxX.Items.Add("foo")
        ListBoxX.Items.Add("bar")

    End Sub

    Private Sub ListBoxX_SelectedIndexChanged(sender As System.Object, e As System.EventArgs) Handles ListBoxX.SelectedIndexChanged
        MessageBox.Show("change registered")
    End Sub

    Private Sub ListBoxX_SelectedValueChanged(sender As Object, e As System.EventArgs) Handles ListBoxX.SelectedValueChanged
        MessageBox.Show("change registered X")
    End Sub
End Class

If “hello” is selected and I then click on “hello” then the message box appears – surely if I’m clicking on the same item then the SelectedIndex has not changed – so why is this event firing? How do I ensure it only fires when the index changes?

Answer 1

Check inside the event if it is the same item as selected before,

Save the last selected item each on click.

Private Sub ListBoxX_SelectedIndexChanged(sender As System.Object, e As System.EventArgs) Handles ListBoxX.SelectedIndexChanged
    if Not LastItem = ListBoxX.SelectedItem Then
        MessageBox.Show("change registered")
        LastItem = ListBoxX.SelectedItem 
    end if
End Sub

It’s been a while since I coded in VB, so I hope this code is OK.

I assume that the event will always fires, no matter which item is selected.

Another solution is to override the ListBox User Control, but I think you don;t need that.