C# Listbox Item Double Click Event

void listBox1_MouseDoubleClick(object sender, MouseEventArgs e)
{
    int index = this.listBox1.IndexFromPoint(e.Location);
    if (index != System.Windows.Forms.ListBox.NoMatches)
    {
        MessageBox.Show(index.ToString());
    }
}

This should work...check

WinForms

Add an event handler for the Control.DoubleClick event for your ListBox, and in that event handler open up a MessageBox displaying the selected item.

E.g.:

 private void ListBox1_DoubleClick(object sender, EventArgs e)
 {
     if (ListBox1.SelectedItem != null)
     {
         MessageBox.Show(ListBox1.SelectedItem.ToString());
     }
 }

Where ListBox1 is the name of your ListBox.

Note that you would assign the event handler like this:

ListBox1.DoubleClick += new EventHandler(ListBox1_DoubleClick);

---

WPF
Pretty much the same as above, but you'd use the MouseDoubleClick event instead:

ListBox1.MouseDoubleClick += new RoutedEventHandler(ListBox1_MouseDoubleClick);

And the event handler:

 private void ListBox1_MouseDoubleClick(object sender, RoutedEventArgs e)
 {
     if (ListBox1.SelectedItem != null)
     {
         MessageBox.Show(ListBox1.SelectedItem.ToString());
     }
 }

---

Edit: Sisya's answer checks to see if the double-click occurred over an item, which would need to be incorporated into this code to fix the issue mentioned in the comments (MessageBox shown if ListBox is double-clicked while an item is selected, but not clicked over an item).

Hope this helps!

I know this question is quite old, but I was looking for a solution to this problem too. The accepted solution is for WinForms not WPF which I think many who come here are looking for.

For anyone looking for a WPF solution, here is a great approach (via Oskar's answer here):

private void myListBox_MouseDoubleClick(object sender, MouseButtonEventArgs e)
{
    DependencyObject obj = (DependencyObject)e.OriginalSource;

    while (obj != null && obj != myListBox)
    {
        if (obj.GetType() == typeof(ListBoxItem))
        {
             // Do something
             break;
         }
         obj = VisualTreeHelper.GetParent(obj);
    }
}

Basically, you walk up the VisualTree until you've either found a parent item that is a ListBoxItem, or you ascend up to the actual ListBox (and therefore did not click a ListBoxItem).