poco/Foundation/include/Poco/NotificationCenter.h

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2006-10-23 17:48:43 +02:00
//
// NotificationCenter.h
//
2008-01-28 18:23:19 +01:00
// $Id: //poco/svn/Foundation/include/Poco/NotificationCenter.h#2 $
2006-10-23 17:48:43 +02:00
//
// Library: Foundation
// Package: Notifications
// Module: NotificationCenter
//
// Definition of the NotificationCenter class.
//
// Copyright (c) 2004-2006, Applied Informatics Software Engineering GmbH.
// and Contributors.
//
// Permission is hereby granted, free of charge, to any person or organization
// obtaining a copy of the software and accompanying documentation covered by
// this license (the "Software") to use, reproduce, display, distribute,
// execute, and transmit the Software, and to prepare derivative works of the
// Software, and to permit third-parties to whom the Software is furnished to
// do so, all subject to the following:
//
// The copyright notices in the Software and this entire statement, including
// the above license grant, this restriction and the following disclaimer,
// must be included in all copies of the Software, in whole or in part, and
// all derivative works of the Software, unless such copies or derivative
// works are solely in the form of machine-executable object code generated by
// a source language processor.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE, TITLE AND NON-INFRINGEMENT. IN NO EVENT
// SHALL THE COPYRIGHT HOLDERS OR ANYONE DISTRIBUTING THE SOFTWARE BE LIABLE
// FOR ANY DAMAGES OR OTHER LIABILITY, WHETHER IN CONTRACT, TORT OR OTHERWISE,
// ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
// DEALINGS IN THE SOFTWARE.
//
#ifndef Foundation_NotificationCenter_INCLUDED
#define Foundation_NotificationCenter_INCLUDED
#include "Poco/Foundation.h"
#include "Poco/Mutex.h"
#include <list>
namespace Poco {
class Notification;
class AbstractObserver;
class Foundation_API NotificationCenter
/// A NotificationCenter is essentially a notification dispatcher.
/// It notifies all observers of notifications meeting specific criteria.
/// This information is encapsulated in Notification objects.
/// Client objects register themselves with the notification center as observers of
/// specific notifications posted by other objects. When an event occurs, an object
/// posts an appropriate notification to the notification center. The notification
/// center invokes the registered method on each matching observer, passing the notification
/// as argument.
///
/// The order in which observers receive notifications is undefined.
/// It is possible for the posting object and the observing object to be the same.
/// The NotificationCenter delivers notifications to observers synchronously.
/// In other words the postNotification() method does not return until all observers have
/// received and processed the notification.
/// If an observer throws an exception while handling a notification, the NotificationCenter
/// stops dispatching the notification and postNotification() rethrows the exception.
///
/// In a multithreaded scenario, notifications are always delivered in the thread in which the
/// notification was posted, which may not be the same thread in which an observer registered itself.
///
/// The NotificationCenter class is basically a C++ implementation of the NSNotificationCenter class
/// found in Apple's Cocoa (or OpenStep).
///
/// While handling a notification, an observer can unregister itself from the notification center,
/// or it can register or unregister other observers. Observers added during a dispatch cycle
/// will not receive the current notification.
///
/// The method receiving the notification must be implemented as
/// void handleNotification(MyNotification* pNf);
/// The handler method gets co-ownership of the Notification object
/// and must release it when done. This is best done with an AutoPtr:
/// void MyClass::handleNotification(MyNotification* pNf)
/// {
/// AutoPtr<MyNotification> nf(pNf);
/// ...
/// }
///
/// Alternatively, the NObserver class template can be used to register a callback
/// method. In this case, the callback method receives the Notification in an
/// AutoPtr and thus does not have to deal with object ownership issues:
/// void MyClass::handleNotification(const AutoPtr<MyNotification>& pNf)
/// {
/// ...
/// }
{
public:
NotificationCenter();
/// Creates the NotificationCenter.
~NotificationCenter();
/// Destroys the NotificationCenter.
void addObserver(const AbstractObserver& observer);
/// Registers an observer with the NotificationCenter.
/// Usage:
/// Observer<MyClass, MyNotification> obs(*this, &MyClass::handleNotification);
/// notificationCenter.addObserver(obs);
///
/// Alternatively, the NObserver template class can be used instead of Observer.
void removeObserver(const AbstractObserver& observer);
/// Unregisters an observer with the NotificationCenter.
void postNotification(Notification* pNotification);
/// Posts a notification to the NotificationCenter.
/// The NotificationCenter then delivers the notification
/// to all interested observers.
/// If an observer throws an exception, dispatching terminates
/// and the exception is rethrown to the caller.
/// Ownership of the notification object is claimed and the
/// notification is released before returning. Therefore,
/// a call like
/// notificationCenter.postNotification(new MyNotification);
/// does not result in a memory leak.
bool hasObservers() const;
/// Returns true iff there is at least one registered observer.
///
/// Can be used to improve performance if an expensive notification
/// shall only be created and posted if there are any observers.
static NotificationCenter& defaultCenter();
/// Returns a reference to the default
/// NotificationCenter.
private:
typedef std::list<AbstractObserver*> ObserverList;
ObserverList _observers;
mutable Mutex _mutex;
};
} // namespace Poco
#endif // Foundation_NotificationCenter_INCLUDED