1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
|
/*******************************************************************************
* Copyright (c) 2005, 2006 IBM Corporation and others.
* All rights reserved. This program and the accompanying materials
* are made available under the terms of the Eclipse Public License v1.0
* which accompanies this distribution, and is available at
* http://www.eclipse.org/legal/epl-v10.html
*
* Contributors:
* IBM Corporation - initial API and implementation
* Brad Reynolds - bug 116920
* Brad Reynolds - bug 147515
*******************************************************************************/
package org.eclipse.core.databinding.observable.value;
import org.eclipse.core.databinding.observable.ChangeEvent;
import org.eclipse.core.databinding.observable.IChangeListener;
import org.eclipse.core.databinding.observable.IObservable;
import org.eclipse.core.databinding.observable.IStaleListener;
import org.eclipse.core.databinding.observable.ObservableTracker;
import org.eclipse.core.databinding.observable.Realm;
import org.eclipse.core.databinding.observable.StaleEvent;
/**
* A Lazily calculated value that automatically computes and registers listeners
* on its dependencies as long as all of its dependencies are IObservable
* objects
*
* @since 1.0
*/
public abstract class ComputedValue extends AbstractObservableValue {
private boolean dirty = true;
private boolean stale = false;
private Object cachedValue = null;
/**
* Dependencies list. This is a collection that contains no duplicates. It
* is normally an ArrayList to conserve memory, but if it ever grows above a
* certain number of elements, a HashSet is substited to conserve runtime.
*/
private IObservable[] dependencies = new IObservable[0];
/**
*
*/
public ComputedValue() {
this(Realm.getDefault(), null);
}
/**
* @param valueType can be <code>null</code>
*/
public ComputedValue(Object valueType) {
this(Realm.getDefault(), valueType);
}
/**
* @param realm
*
*/
public ComputedValue(Realm realm) {
this(realm, null);
}
/**
* @param realm
* @param valueType
*/
public ComputedValue(Realm realm, Object valueType) {
super(realm);
this.valueType = valueType;
}
/**
* Inner class that implements interfaces that we don't want to expose as
* public API. Each interface could have been implemented using a separate
* anonymous class, but we combine them here to reduce the memory overhead
* and number of classes.
*
* <p>
* The Runnable calls computeValue and stores the result in cachedValue.
* </p>
*
* <p>
* The IChangeListener stores each observable in the dependencies list.
* This is registered as the listener when calling ObservableTracker, to
* detect every observable that is used by computeValue.
* </p>
*
* <p>
* The IChangeListener is attached to every dependency.
* </p>
*
*/
private class PrivateInterface implements Runnable, IChangeListener,
IStaleListener {
public void run() {
cachedValue = calculate();
}
public void handleStale(StaleEvent event) {
if (!dirty && !stale) {
stale = true;
fireStale();
}
}
public void handleChange(ChangeEvent event) {
makeDirty();
}
}
private PrivateInterface privateInterface = new PrivateInterface();
private Object valueType;
protected final Object doGetValue() {
if (dirty) {
// This line will do the following:
// - Run the calculate method
// - While doing so, add any observable that is touched to the
// dependencies list
IObservable[] newDependencies = ObservableTracker.runAndMonitor(
privateInterface, privateInterface, null);
stale = false;
for (int i = 0; i < newDependencies.length; i++) {
IObservable observable = newDependencies[i];
// Add a change listener to the new dependency.
if (observable.isStale()) {
stale = true;
} else {
observable.addStaleListener(privateInterface);
}
}
dependencies = newDependencies;
dirty = false;
}
return cachedValue;
}
/**
* Subclasses must override this method to provide the object's value.
*
* @return the object's value
*/
protected abstract Object calculate();
protected final void makeDirty() {
if (!dirty) {
dirty = true;
// Stop listening for dependency changes.
for (int i = 0; i < dependencies.length; i++) {
IObservable observable = dependencies[i];
observable.removeChangeListener(privateInterface);
observable.removeStaleListener(privateInterface);
}
// copy the old value
final Object oldValue = cachedValue;
// Fire the "dirty" event. This implementation recomputes the new
// value lazily.
fireValueChange(new ValueDiff() {
public Object getOldValue() {
return oldValue;
}
public Object getNewValue() {
return getValue();
}
});
}
}
public boolean isStale() {
// we need to recompute, otherwise staleness wouldn't mean anything
getValue();
return stale;
}
public Object getValueType() {
return valueType;
}
public void addChangeListener(IChangeListener listener) {
super.addChangeListener(listener);
// If somebody is listening, we need to make sure we attach our own
// listeners
getValue();
}
public void addValueChangeListener(IValueChangeListener listener) {
super.addValueChangeListener(listener);
// If somebody is listening, we need to make sure we attach our own
// listeners
getValue();
}
}
|
