src/apps/cortex/support/IObservable.h

   1 /*
   2  * Copyright (c) 1999-2000, Eric Moon.
   3  * All rights reserved.
   4  *
   5  * Redistribution and use in source and binary forms, with or without
   6  * modification, are permitted provided that the following conditions
   7  * are met:
   8  *
   9  * 1. Redistributions of source code must retain the above copyright
  10  *    notice, this list of conditions, and the following disclaimer.
  11  *
  12  * 2. Redistributions in binary form must reproduce the above copyright
  13  *    notice, this list of conditions, and the following disclaimer in the
  14  *    documentation and/or other materials provided with the distribution.
  15  *
  16  * 3. The name of the author may not be used to endorse or promote products
  17  *    derived from this software without specific prior written permission.
  18  *
  19  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR "AS IS" AND ANY EXPRESS OR
  20  * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
  21  * OF TITLE, NON-INFRINGEMENT, MERCHANTABILITY AND FITNESS FOR A PARTICULAR
  22  * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY
  23  * DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
  24  * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
  25  * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
  26  * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR
  27  * TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
  28  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  29  */
  30
  31
  32 // IObservable.h
  33 // * PURPOSE
  34 //   Defines a general observable-object interface.
  35 // * HISTORY
  36 //   e.moon             19aug99         Begun
  37
  38 #ifndef __IObservable_H__
  39 #define __IObservable_H__
  40
  41 class BMessenger;
  42
  43 #include "cortex_defs.h"
  44 __BEGIN_CORTEX_NAMESPACE
  45
  46 class IObservable {
  47
  48 public:
  49         IObservable() { }
  50         virtual ~IObservable() { }
  51 public:                                                                                 // *** deletion
  52         // clients must call release() rather than deleting,
  53         // to ensure that all observers are notified of the
  54         // object's demise.  if the object has already been
  55         // released, return an error.
  56         virtual status_t release()=0;
  57
  58 public:                                                                                 // *** accessors
  59         // return true if release() has been called, false otherwise.
  60         virtual bool isReleased() const=0;
  61
  62 protected:                                                                      // *** hooks
  63         // must be called after an observer has been added (this is a good
  64         // place to send an acknowledgement)
  65         virtual void observerAdded(
  66                 const BMessenger&                               observer) {TOUCH(observer);}
  67
  68         // must be called after an observer has been removed
  69         virtual void observerRemoved(
  70                 const BMessenger&                               observer) {TOUCH(observer);}
  71
  72         // must be called once all observers have been removed
  73         virtual void releaseComplete() {}
  74
  75 protected:                                                                      // *** operations
  76         // call to send the given message to all observers.
  77         // Responsibility for deletion of the message remains with
  78         // the caller.
  79         virtual status_t notify(
  80                 BMessage*                                                               message)=0;
  81
  82         // must be called by release() if targets remain to be
  83         // released.  should notify all targets with an appropriate
  84         // release-notification message (such as M_RELEASE_OBSERVABLE).
  85         virtual void notifyRelease()=0;
  86 };
  87
  88 __END_CORTEX_NAMESPACE
  89 #endif /*__IObservable_H__*/