/// <summary>
/// Registers an event handler that works with a weak reference to the target object.
/// Access to the event and to the real event handler is done through lambda expressions.
/// The code holds strong references to these expressions, so they must not capture any
/// variables!
/// </summary>
/// <example>
/// <code>
/// WeakEventHandler.Register(
/// textDocument,
/// (d, eh) => d.Changed += eh,
/// (d, eh) => d.Changed -= eh,
/// this,
/// (me, sender, args) => me.OnDocumentChanged(sender, args)
/// );
/// </code>
/// </example>
public static WeakEventHandler Register <TEventSource, TEventListener>(
TEventSource senderObject,
ZetaAction <TEventSource, EventHandler> registerEvent,
ZetaAction <TEventSource, EventHandler> deregisterEvent,
TEventListener listeningObject,
ZetaAction <TEventListener, object, EventArgs> forwarderAction
)
where TEventSource : class
where TEventListener : class
{
if (senderObject == null)
{
throw new ArgumentNullException(nameof(senderObject));
}
if (listeningObject == null)
{
throw new ArgumentNullException(nameof(listeningObject));
}
VerifyDelegate(registerEvent, @"registerEvent");
VerifyDelegate(deregisterEvent, @"deregisterEvent");
VerifyDelegate(forwarderAction, @"forwarderAction");
var weh = new WeakEventHandler(listeningObject);
var eh = weh.MakeDeregisterCodeAndWeakEventHandler(senderObject, deregisterEvent, forwarderAction);
registerEvent(senderObject, eh);
return(weh);
}
EventHandler MakeDeregisterCodeAndWeakEventHandler
<TEventSource, TEventListener>
(
TEventSource senderObject,
ZetaAction <TEventSource, EventHandler> deregisterEvent,
ZetaAction <TEventListener, object, EventArgs> forwarderAction
)
where TEventSource : class
where TEventListener : class
{
EventHandler eventHandler = null;
DeregisterCode = () => deregisterEvent(senderObject, eventHandler);
eventHandler = (sender, args) =>
{
var listeningObject = (TEventListener)ListeningReference.Target;
if (listeningObject != null)
{
forwarderAction(listeningObject, sender, args);
}
else
{
Deregister();
}
};
return(eventHandler);
}
/// <summary>
/// Deregisters the event handler.
/// </summary>
public void Deregister()
{
if (DeregisterCode != null)
{
DeregisterCode();
DeregisterCode = null;
}
}
