Question

How to raise the SelectedIndexChanged event of an asp.net List control in a codebehind using C#?

Answer 1

If you’re asking how to manually fire the event so that it can run whatever logic is attached: don’t.

Your event handlers should be slim. If you need to perform the same operation from multiple places, then extract that functionality into its own method and have the event handler invoke that. For example:

private void CountryListBox_SelectedIndexChanged(object sender, EventArgs e)
{
    UpdateStates(ListBox1.SelectedItem.Text);
}

private void UpdateStates(string country)
{
    StateListBox.DataSource = GetStates(country);
    StateListBox.DataBind();
}

Now instead of trying to fire the SelectedIndexChanged event, you just invoke the method that this event handler refers to, i.e.

private void Page_Load(object sender, EventArgs e)
{
    UpdateStates("USA");
}

Don’t put complex logic in event handlers and try to raise those events from unexpected places. Instead, put the complex logic in its own method, so that you can perform the associated actions from elsewhere.