Removing a control's behavior

In Programming .NET Components, Juval Löwy explains the reasoning behind and how to use the EventHandlerList class (it’s used internally in the Control and derived classes to store event subscriptions).

I found that this architecture easily supports the removal of all behavior*:

public static void ClearEventHandlerList (Component component) {
    if (component == null)
        throw new ArgumentNullException ("component");
    FieldInfo fieldInfo = (typeof (Component)).GetField ("events",
        BindingFlags.Instance |
        BindingFlags.NonPublic |
        BindingFlags.DeclaredOnly |
        BindingFlags.ExactBinding);
    EventHandlerList currentList =
        fieldInfo.GetValue (component) as EventHandlerList;
    if (currentList != null)
        currentList.Dispose ();
    fieldInfo.SetValue (component, null);
}

For example, a security component could easily remove a control’s behavior* when the user does not have permission. Keep in mind that this is not a substitute for declarative or imperative security checks — other methods can continue to refer to the control’s state or subscribe to its events in the future.

Other benefits include the ability for a security component to use a ToolTip to notify the user of access denied (ToolTips do not function on disabled controls).

button.Click += new System.EventHandler (this.button_Click);
// the button_Click method is called when the button is clicked
...
ClearEventHandlerList (button);
// button does not have a click event subscriber anymore
// (button_Click is no longer called when the button is clicked)

* behavior as defined by event subscriptions where the event accessor implementation uses the EventHandlerList class.