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
41class BMessenger;
42
43#include "cortex_defs.h"
44__BEGIN_CORTEX_NAMESPACE
45
46class IObservable {
47
48public:
49	IObservable() { }
50	virtual ~IObservable() { }
51public:											// *** 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
58public:											// *** accessors
59	// return true if release() has been called, false otherwise.
60	virtual bool isReleased() const=0;
61
62protected:									// *** 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
75protected:									// *** 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__*/
90