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annotate org.eclipse.core.databinding.observable/src/org/eclipse/core/databinding/observable/value/ComputedValue.d @ 96:b74ac5dfcc06

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package to module and java.lang.all import
author Frank Benoit <benoit@tionex.de>
date Tue, 21 Apr 2009 11:03:33 +0200
parents 6208d4f6a277
children c86eb8b3098e
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1 /*******************************************************************************
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2 * Copyright (c) 2005, 2008 IBM Corporation and others.
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3 * All rights reserved. This program and the accompanying materials
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4 * are made available under the terms of the Eclipse Public License v1.0
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5 * which accompanies this distribution, and is available at
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6 * http://www.eclipse.org/legal/epl-v10.html
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7 *
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8 * Contributors:
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9 * IBM Corporation - initial API and implementation
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10 * Brad Reynolds - bug 116920
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11 * Brad Reynolds - bug 147515
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12 *******************************************************************************/
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13 module org.eclipse.core.databinding.observable.value.ComputedValue;
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14
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15 import java.lang.all;
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16
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17 import org.eclipse.core.databinding.observable.ChangeEvent;
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18 import org.eclipse.core.databinding.observable.IChangeListener;
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19 import org.eclipse.core.databinding.observable.IObservable;
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20 import org.eclipse.core.databinding.observable.IStaleListener;
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21 import org.eclipse.core.databinding.observable.ObservableTracker;
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22 import org.eclipse.core.databinding.observable.Realm;
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23 import org.eclipse.core.databinding.observable.StaleEvent;
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24
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25 /**
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26 * A Lazily calculated value that automatically computes and registers listeners
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27 * on its dependencies as long as all of its dependencies are IObservable
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28 * objects
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29 * <p>
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30 * This class is thread safe. All state accessing methods must be invoked from
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31 * the {@link Realm#isCurrent() current realm}. Methods for adding and removing
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32 * listeners may be invoked from any thread.
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33 * </p>
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34 *
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35 * @since 1.0
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36 */
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37 public abstract class ComputedValue : AbstractObservableValue {
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38
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39 private bool dirty = true;
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40
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41 private bool stale = false;
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42
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43 private Object cachedValue = null;
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44
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45 /**
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46 * Array of observables this computed value depends on. This field has a
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47 * value of <code>null</code> if we are not currently listening.
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48 */
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49 private IObservable[] dependencies = null;
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50
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51 /**
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52 *
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53 */
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54 public this() {
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55 this(Realm.getDefault(), null);
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56 }
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57
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58 /**
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59 * @param valueType
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60 * can be <code>null</code>
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61 */
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62 public this(Object valueType) {
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63 this(Realm.getDefault(), valueType);
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64 }
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65
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66 /**
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67 * @param realm
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68 *
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69 */
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70 public this(Realm realm) {
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71 this(realm, null);
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72 }
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73
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74 /**
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75 * @param realm
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76 * @param valueType
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77 */
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78 public this(Realm realm, Object valueType) {
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79 super(realm);
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80 this.valueType = valueType;
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81 }
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82
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83 /**
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84 * Inner class that implements interfaces that we don't want to expose as
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85 * public API. Each interface could have been implemented using a separate
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86 * anonymous class, but we combine them here to reduce the memory overhead
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87 * and number of classes.
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88 *
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89 * <p>
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90 * The Runnable calls computeValue and stores the result in cachedValue.
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91 * </p>
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92 *
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93 * <p>
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94 * The IChangeListener stores each observable in the dependencies list. This
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95 * is registered as the listener when calling ObservableTracker, to detect
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96 * every observable that is used by computeValue.
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97 * </p>
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98 *
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99 * <p>
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100 * The IChangeListener is attached to every dependency.
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101 * </p>
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102 *
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103 */
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104 private class PrivateInterface : Runnable, IChangeListener,
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105 IStaleListener {
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106 public void run() {
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107 cachedValue = calculate();
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108 }
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109
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110 public void handleStale(StaleEvent event) {
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111 if (!dirty && !stale) {
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112 stale = true;
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113 fireStale();
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114 }
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115 }
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116
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117 public void handleChange(ChangeEvent event) {
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118 makeDirty();
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119 }
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120 }
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121
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122 private PrivateInterface privateInterface = new PrivateInterface();
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123
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124 private Object valueType;
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125
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126 protected final Object doGetValue() {
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127 if (dirty) {
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128 // This line will do the following:
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129 // - Run the calculate method
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130 // - While doing so, add any observable that is touched to the
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131 // dependencies list
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132 IObservable[] newDependencies = ObservableTracker.runAndMonitor(
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133 privateInterface, privateInterface, null);
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134
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135 stale = false;
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136 for (int i = 0; i < newDependencies.length; i++) {
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137 IObservable observable = newDependencies[i];
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138 // Add a change listener to the new dependency.
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139 if (observable.isStale()) {
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140 stale = true;
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141 } else {
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142 observable.addStaleListener(privateInterface);
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143 }
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144 }
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145
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146 dependencies = newDependencies;
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147
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148 dirty = false;
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149 }
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150
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151 return cachedValue;
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152 }
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153
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154 /**
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155 * Subclasses must override this method to provide the object's value.
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156 *
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157 * @return the object's value
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158 */
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159 protected abstract Object calculate();
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160
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161 protected final void makeDirty() {
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162 if (!dirty) {
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163 dirty = true;
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164
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165 stopListening();
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166
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167 // copy the old value
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168 final Object oldValue = cachedValue;
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169 // Fire the "dirty" event. This implementation recomputes the new
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170 // value lazily.
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171 fireValueChange(new class() ValueDiff {
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172
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173 public Object getOldValue() {
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174 return oldValue;
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175 }
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176
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177 public Object getNewValue() {
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178 return getValue();
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179 }
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180 });
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181 }
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182 }
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183
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184 /**
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185 *
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186 */
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187 private void stopListening() {
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188 // Stop listening for dependency changes.
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189 if (dependencies !is null) {
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190 for (int i = 0; i < dependencies.length; i++) {
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191 IObservable observable = dependencies[i];
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192
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193 observable.removeChangeListener(privateInterface);
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194 observable.removeStaleListener(privateInterface);
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195 }
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196 dependencies = null;
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197 }
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198 }
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199
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200 public bool isStale() {
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201 // we need to recompute, otherwise staleness wouldn't mean anything
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202 getValue();
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203 return stale;
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204 }
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205
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206 public Object getValueType() {
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207 return valueType;
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208 }
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209
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210 // this method exists here so that we can call it from the runnable below.
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211 /**
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212 * @since 1.1
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213 */
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214 protected bool hasListeners() {
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215 return super.hasListeners();
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216 }
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217
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218 public synchronized void addChangeListener(IChangeListener listener) {
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219 super.addChangeListener(listener);
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220 // If somebody is listening, we need to make sure we attach our own
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221 // listeners
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222 computeValueForListeners();
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223 }
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224
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225 /**
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226 * Some clients just add a listener and expect to get notified even if they
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227 * never called getValue(), so we have to call getValue() ourselves here to
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228 * be sure. Need to be careful about realms though, this method can be
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229 * called outside of our realm. See also bug 198211. If a client calls this
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230 * outside of our realm, they may receive change notifications before the
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231 * runnable below has been executed. It is their job to figure out what to
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232 * do with those notifications.
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233 */
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234 private void computeValueForListeners() {
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235 getRealm().exec(new class() Runnable {
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236 public void run() {
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237 if (dependencies is null) {
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238 // We are not currently listening.
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239 if (hasListeners()) {
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240 // But someone is listening for changes. Call getValue()
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241 // to make sure we start listening to the observables we
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242 // depend on.
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243 getValue();
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244 }
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245 }
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246 }
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247 });
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248 }
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249
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250 public synchronized void addValueChangeListener(
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251 IValueChangeListener listener) {
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252 super.addValueChangeListener(listener);
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253 // If somebody is listening, we need to make sure we attach our own
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254 // listeners
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255 computeValueForListeners();
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256 }
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257
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258 public synchronized void dispose() {
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259 super.dispose();
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260 stopListening();
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261 }
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262
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263 }