1 /*
2 * Copyright (c) 2010, 2013, Oracle and/or its affiliates. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 *
5 * This code is free software; you can redistribute it and/or modify it
6 * under the terms of the GNU General Public License version 2 only, as
7 * published by the Free Software Foundation. Oracle designates this
8 * particular file as subject to the "Classpath" exception as provided
9 * by Oracle in the LICENSE file that accompanied this code.
10 *
11 * This code is distributed in the hope that it will be useful, but WITHOUT
12 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
13 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
14 * version 2 for more details (a copy is included in the LICENSE file that
15 * accompanied this code).
16 *
17 * You should have received a copy of the GNU General Public License version
18 * 2 along with this work; if not, write to the Free Software Foundation,
19 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
20 *
21 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
22 * or visit www.oracle.com if you need additional information or have any
23 * questions.
24 */
25
26 package javafx.beans.binding;
27
28 import javafx.beans.InvalidationListener;
29 import javafx.beans.Observable;
30 import javafx.beans.value.ChangeListener;
31 import javafx.collections.FXCollections;
32 import javafx.collections.ObservableList;
33 import com.sun.javafx.collections.annotations.ReturnsUnmodifiableCollection;
34
35 import com.sun.javafx.binding.BindingHelperObserver;
36 import com.sun.javafx.binding.ExpressionHelper;
37
38 /**
39 * Base class that provides most of the functionality needed to implement a
40 * {@link Binding} of a {@code double} value.
41 * <p>
42 * {@code DoubleBinding} provides a simple invalidation-scheme. An extending
43 * class can register dependencies by calling {@link #bind(Observable...)}.
44 * If One of the registered dependencies becomes invalid, this
45 * {@code DoubleBinding} is marked as invalid. With
46 * {@link #unbind(Observable...)} listening to dependencies can be stopped.
47 * <p>
48 * To provide a concrete implementation of this class, the method
49 * {@link #computeValue()} has to be implemented to calculate the value of this
50 * binding based on the current state of the dependencies. It is called when
51 * {@link #get()} is called for an invalid binding.
52 * <p>
53 * Below is a simple example of a {@code DoubleBinding} calculating the square-
54 * root of a {@link javafx.beans.value.ObservableNumberValue} {@code moo}.
55 *
56 * <pre>
57 * <code>
58 * final ObservableDoubleValue moo = ...;
59 *
60 * DoubleBinding foo = new DoubleBinding() {
61 *
62 * {
63 * super.bind(moo);
64 * }
65 *
66 * @Override
67 * protected double computeValue() {
68 * return Math.sqrt(moo.getValue());
69 * }
70 * };
71 * </code>
72 * </pre>
73 *
74 * Following is the same example with implementations for the optional methods
75 * {@link Binding#getDependencies()} and {@link Binding#dispose()}.
76 *
77 * <pre>
78 * <code>
79 * final ObservableDoubleValue moo = ...;
80 *
81 * DoubleBinding foo = new DoubleBinding() {
82 *
83 * {
84 * super.bind(moo);
85 * }
86 *
87 * @Override
88 * protected double computeValue() {
89 * return Math.sqrt(moo.getValue());
90 * }
91 *
92 * @Override
93 * public ObservableList<?> getDependencies() {
94 * return FXCollections.singletonObservableList(moo);
95 * }
96 *
97 * @Override
98 * public void dispose() {
99 * super.unbind(moo);
100 * }
101 * };
102 * </code>
103 * </pre>
104 *
105 * @see Binding
106 * @see NumberBinding
107 * @see javafx.beans.binding.DoubleExpression
108 *
109 *
110 * @since JavaFX 2.0
111 */
112 public abstract class DoubleBinding extends DoubleExpression implements
113 NumberBinding {
114
115 private double value;
116 private boolean valid;
117 private BindingHelperObserver observer;
118 private ExpressionHelper<Number> helper = null;
119
120 @Override
121 public void addListener(InvalidationListener listener) {
122 helper = ExpressionHelper.addListener(helper, this, listener);
123 }
124
125 @Override
126 public void removeListener(InvalidationListener listener) {
127 helper = ExpressionHelper.removeListener(helper, listener);
128 }
129
130 @Override
131 public void addListener(ChangeListener<? super Number> listener) {
132 helper = ExpressionHelper.addListener(helper, this, listener);
133 }
134
135 @Override
136 public void removeListener(ChangeListener<? super Number> listener) {
137 helper = ExpressionHelper.removeListener(helper, listener);
138 }
139
140 /**
141 * Start observing the dependencies for changes. If the value of one of the
142 * dependencies changes, the binding is marked as invalid.
143 *
144 * @param dependencies
145 * the dependencies to observe
146 */
147 protected final void bind(Observable... dependencies) {
148 if ((dependencies != null) && (dependencies.length > 0)) {
149 if (observer == null) {
150 observer = new BindingHelperObserver(this);
151 }
152 for (final Observable dep : dependencies) {
153 dep.addListener(observer);
154 }
155 }
156 }
157
158 /**
159 * Stop observing the dependencies for changes.
160 *
161 * @param dependencies
162 * the dependencies to stop observing
163 */
164 protected final void unbind(Observable... dependencies) {
165 if (observer != null) {
166 for (final Observable dep : dependencies) {
167 dep.removeListener(observer);
168 }
169 observer = null;
170 }
171 }
172
173 /**
174 * A default implementation of {@code dispose()} that is empty.
175 */
176 @Override
177 public void dispose() {
178 }
179
180 /**
181 * A default implementation of {@code getDependencies()} that returns an
182 * empty {@link javafx.collections.ObservableList}.
183 *
184 * @return an empty {@code ObservableList}
185 */
186 @Override
187 @ReturnsUnmodifiableCollection
188 public ObservableList<?> getDependencies() {
189 return FXCollections.emptyObservableList();
190 }
191
192 /**
193 * Returns the result of {@link #computeValue()}. The method
194 * {@code computeValue()} is only called if the binding is invalid. The
195 * result is cached and returned if the binding did not become invalid since
196 * the last call of {@code get()}.
197 *
198 * @return the current value
199 */
200 @Override
201 public final double get() {
202 if (!valid) {
203 value = computeValue();
204 valid = true;
205 }
206 return value;
207 }
208
209 /**
210 * The method onInvalidating() can be overridden by extending classes to
211 * react, if this binding becomes invalid. The default implementation is
212 * empty.
213 */
214 protected void onInvalidating() {
215 }
216
217 @Override
218 public final void invalidate() {
219 if (valid) {
220 valid = false;
221 onInvalidating();
222 ExpressionHelper.fireValueChangedEvent(helper);
223 }
224 }
225
226 @Override
227 public final boolean isValid() {
228 return valid;
229 }
230
231 /**
232 * Calculates the current value of this binding.
233 * <p>
234 * Classes extending {@code DoubleBinding} have to provide an implementation
235 * of {@code computeValue}.
236 *
237 * @return the current value
238 */
239 protected abstract double computeValue();
240
241 /**
242 * Returns a string representation of this {@code DoubleBinding} object.
243 * @return a string representation of this {@code DoubleBinding} object.
244 */
245 @Override
246 public String toString() {
247 return valid ? "DoubleBinding [value: " + get() + "]"
248 : "DoubleBinding [invalid]";
249 }
250 }