Attached propedrties in WPF and event wiring

I have an attached property (e.g. its capitalizing the text inside a TextBox). Obvoiusly I must subscribe to the TextBox's TextChanged event to capitalize it every time text updates.

public class Capitalize
{
    // this is for enabling/disabling capitalization
    public static readonly DependencyProperty EnabledProperty;
    private static void OnEnabledChanged(
        DependencyObject d, 
        DependencyPropertyChangedEventArgs e)
    {
        var tb = d as TextBox;
        if ((bool)e.NewValue)
        {
            tb.Text开发者_运维百科Changed += new TextChangedEventHandler(tb_TextChanged);
        }
        else
        {
            tb.TextChanged -= new TextChangedEventHandler(tb_TextChanged);
        }
    }
}

As we see we add event handlers to the TextBox which (if I understand correctly) creates a strong reference. Does this also mean that because of that strong ref the GC cannot collect the TextBox? If yes - at which point should I unwire the event so that the TextBox can be collected?

The reference goes the other way around, i.e. the text box holds the reference to the event handler. So there is no possibility for memory leaks.