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NotificationCenter.h

//
// NotificationCenter.h
//
// $Id: //poco/1.3/Foundation/include/Poco/NotificationCenter.h#3 $
//
// 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/Notification.h"
#include "Poco/Mutex.h"
#include "Poco/SharedPtr.h"
#include <vector>
#include <cstddef>


namespace Poco {


class AbstractObserver;


00057 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::Ptr 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.
            
      std::size_t countObservers() const;
            /// Returns the number of registered observers.
            
      static NotificationCenter& defaultCenter();
            /// Returns a reference to the default
            /// NotificationCenter.

private:
00147       typedef Poco::SharedPtr<AbstractObserver> AbstractObserverPtr;
      typedef std::vector<AbstractObserverPtr> ObserverList;

      ObserverList  _observers;
      mutable Mutex _mutex;
};


} // namespace Poco


#endif // Foundation_NotificationCenter_INCLUDED

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