1 /*
2 * Copyright (c) 2010, 2017, 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.scene.control;
27
28 import javafx.beans.InvalidationListener;
29 import javafx.beans.Observable;
30 import javafx.beans.property.BooleanProperty;
31 import javafx.beans.property.ObjectProperty;
32 import javafx.beans.property.SimpleBooleanProperty;
33 import javafx.beans.property.SimpleObjectProperty;
34 import javafx.collections.ObservableList;
35 import javafx.scene.Node;
36 import javafx.scene.layout.GridPane;
37 import javafx.scene.layout.HBox;
38 import javafx.scene.shape.Rectangle;
39 import javafx.css.PseudoClass;
40 import javafx.beans.property.ReadOnlyBooleanProperty;
41 import javafx.beans.property.ReadOnlyBooleanWrapper;
42 import javafx.beans.value.WritableValue;
43 import javafx.css.StyleableProperty;
44
45 /**
46 * The Cell API is used for virtualized controls such as {@link ListView},
47 * {@link TreeView}, and {@link TableView}.
48 * A Cell is a {@link Labeled} {@link Control}, and is used to render a single
49 * "row" inside a ListView, TreeView or TableView. Cells are also used for each
50 * individual 'cell' inside a TableView (i.e. each row/column intersection). See
51 * the JavaDoc for each control separately for more detail.
52 * <p>
53 * Every Cell is associated with a single data item (represented by the
54 * {@link #itemProperty() item} property). The Cell is responsible for
55 * rendering that item and, where appropriate, for editing the item. An item
56 * within a Cell may be represented by text or some other control such as a
57 * {@link CheckBox}, {@link ChoiceBox} or any other {@link Node} such as a
58 * {@link HBox}, {@link GridPane}, or even a {@link Rectangle}.
59 * <p>
60 * Because TreeView, ListView, TableView and other such controls can potentially
61 * be used for displaying incredibly large amounts of data, it is not feasible
62 * to create an actual Cell for every single item in the control.
63 * We represent extremely large data sets using only very few Cells. Each Cell
64 * is "recycled", or reused. This is what we mean when we say that these controls
65 * are virtualized.
66 * <p>
67 * Since Cell is a Control, it is essentially a "model". Its Skin is responsible
68 * for defining the look and layout, while the Behavior is responsible for
69 * handling all input events and using that information to modify the Control
70 * state. Also, the Cell is styled from CSS just like any other Control.
71 * However, it is not necessary to implement a Skin for most uses of a Cell.
72 * This is because a cell factory can be set - this is detailed more shortly.
73 * <p>
74 * Because by far the most common use case for cells is to show text to a user,
75 * this use case is specially optimized for within Cell. This is done by Cell
76 * extending from {@link Labeled}. This means that subclasses of Cell need only
77 * set the {@link #textProperty() text} property, rather than create a separate
78 * {@link Label} and set that within the Cell. However, for situations where
79 * something more than just plain text is called for, it is possible to place
80 * any {@link Node} in the Cell {@link #graphicProperty() graphic} property.
81 * Despite the term, a graphic can be any Node, and will be fully interactive.
82 * For example, a ListCell might be configured with a {@link Button} as its
83 * graphic. The Button text could then be bound to the cells
84 * {@link #itemProperty() item} property. In this way, whenever the item in the
85 * Cell changes, the Button text is automatically updated.
86 * <p>
87 * Cell sets focusTraversable to false.
88 * </p>
89 * <p>
90 * <b>Cell Factories</b>
91 * <p>
92 * The default representation of the Cell <code>item</code> is up to the various
93 * virtualized container's skins to render. For example, the ListView by default
94 * will convert the item to a String and call {@link #setText(java.lang.String)}
95 * with this value. If you want to specialize the Cell used for the
96 * ListView (for example), then you must provide an implementation of the
97 * {@link ListView#cellFactoryProperty() cellFactory} callback function defined
98 * on the ListView. Similar API exists on most controls that use Cells (for example,
99 * {@link TreeView#cellFactoryProperty() TreeView},
100 * {@link TableView#rowFactoryProperty() TableView},
101 * {@link TableColumn#cellFactoryProperty() TableColumn} and
102 * {@link ListView#cellFactoryProperty() ListView}.
103 * <p>
104 * The cell factory is called by the platform whenever it determines that a new
105 * cell needs to be created. For example, perhaps your ListView has 10 million
106 * items. Creating all 10 million cells would be prohibitively expensive. So
107 * instead the ListView skin implementation might only create just enough cells
108 * to fit the visual space. If the ListView is resized to be larger, the system
109 * will determine that it needs to create some additional cells. In this case
110 * it will call the cellFactory callback function (if one is provided) to create
111 * the Cell implementation that should be used. If no cell factory is provided,
112 * the built-in default implementation will be used.
113 * <p>
114 * The implementation of the cell factory is then responsible not just for
115 * creating a Cell instance, but also configuring that Cell such that it reacts
116 * to changes in its state. For example, if I were to create
117 * a custom Cell which formatted Numbers such that they would appear as currency
118 * types, I might do so like this:
119 *
120 * <pre>
121 * public class MoneyFormatCell extends ListCell<Number> {
122 *
123 * public MoneyFormatCell() { }
124 *
125 * @Override protected void updateItem(Number item, boolean empty) {
126 * // calling super here is very important - don't skip this!
127 * super.updateItem(item, empty);
128 *
129 * // format the number as if it were a monetary value using the
130 * // formatting relevant to the current locale. This would format
131 * // 43.68 as "$43.68", and -23.67 as "-$23.67"
132 * setText(item == null ? "" : NumberFormat.getCurrencyInstance().format(item));
133 *
134 * // change the text fill based on whether it is positive (green)
135 * // or negative (red). If the cell is selected, the text will
136 * // always be white (so that it can be read against the blue
137 * // background), and if the value is zero, we'll make it black.
138 * if (item != null) {
139 * double value = item.doubleValue();
140 * setTextFill(isSelected() ? Color.WHITE :
141 * value == 0 ? Color.BLACK :
142 * value < 0 ? Color.RED : Color.GREEN);
143 * }
144 * }
145 * }</pre>
146 *
147 * This class could then be used inside a ListView as such:
148 *
149 * <pre>
150 * ObservableList<Number> money = ...;
151 * final ListView<Number> listView = new ListView<Number>(money);
152 * listView.setCellFactory(new Callback<ListView<Number>, ListCell<Number>>() {
153 * @Override public ListCell<Number> call(ListView<Number> list) {
154 * return new MoneyFormatCell();
155 * }
156 * });</pre>
157 *
158 * In this example an anonymous inner class is created, that simply returns
159 * instances of MoneyFormatCell whenever it is called. The MoneyFormatCell class
160 * extends {@link ListCell}, overriding the
161 * {@link #updateItem(java.lang.Object, boolean) updateItem} method. This method
162 * is called whenever the item in the cell changes, for example when the user
163 * scrolls the ListView or the content of the underlying data model changes
164 * (and the cell is reused to represent some different item in the ListView).
165 * Because of this, there is no need to manage bindings - simply react to the
166 * change in items when this method occurs. In the example above, whenever the
167 * item changes, we update the cell text property, and also modify the text fill
168 * to ensure that we get the correct visuals. In addition, if the cell is "empty"
169 * (meaning it is used to fill out space in the ListView but doesn't have any
170 * data associated with it), then we just use the empty String.
171 * <p>
172 * Note that there are additional
173 * methods prefixed with 'update' that may be of interest, so be
174 * sure to read the API documentation for Cell, and subclasses of Cell, closely.
175 * <p>
176 * Of course, we can also use the binding API rather than overriding the
177 * 'update' methods. Shown below is a very trivial example of how this could
178 * be achieved.
179 *
180 *
181 * <pre>
182 * public class BoundLabelCell extends ListCell<String> {
183 *
184 * public BoundLabelCell() {
185 * textProperty().bind(itemProperty());
186 * }
187 * }
188 * </pre>
189 *
190 * <h3>Key Design Goals</h3>
191 * <ul>
192 * <li>Both time and memory efficient for large data sets</li>
193 * <li>Easy to build and use libraries for custom cells</li>
194 * <li>Easy to customize cell visuals</li>
195 * <li>Easy to customize display formatting (12.34 as $12.34 or 1234% etc)</li>
196 * <li>Easy to extend for custom visuals</li>
197 * <li>Easy to have "panels" of data for the visuals</li>
198 * <li>Easy to animate the cell size or other properties</li>
199 * </ul>
200 *
201 * <h3>Key Use Cases</h3>
202 * Following are a number of key use cases used to drive the Cell API design,
203 * along with code examples showing how those use cases are satisfied by this
204 * API. This is by no means to be considered the definitive list of capabilities
205 * or features supported, but rather, to provide some guidance as to how to use
206 * the Cell API. The examples below are focused on the ListView, but the same
207 * philosophy applies to TreeCells or other kinds of cells.
208 * <p>
209 * <b>Changing the Cell's Colors</b>
210 * <p>
211 * This should be extraordinarily simple in JavaFX. Each Cell can be styled
212 * directly from CSS. So for example, if you wanted to change the default
213 * background of every cell in a ListView to be WHITE you could do the
214 * following CSS:
215 *
216 * <pre>
217 * .list-cell {
218 * -fx-padding: 3 3 3 3;
219 * -fx-background-color: white;
220 * }</pre>
221 *
222 * If you wanted to set the color of selected ListView cells to be blue, you
223 * could add this to your CSS file:
224 *
225 * <pre>
226 * .list-cell:selected {
227 * -fx-background-color: blue;
228 * }</pre>
229 *
230 * Most Cell implementations extend from {@link IndexedCell} rather than Cell.
231 * IndexedCell adds two other pseudoclass states: "odd" and "even". Using this
232 * you can get alternate row striping by doing something like this in your CSS
233 * file:
234 *
235 * <pre>
236 * .list-cell:odd {
237 * -fx-background-color: grey;
238 * }</pre>
239 *
240 * Each of these examples require no code changes. Simply update your CSS
241 * file to alter the colors. You can also use the "hover" and other
242 * pseudoclasses in CSS the same as with other controls.
243 * <p>
244 * Another approach to the first example above (formatting a list of numbers) would
245 * be to use style classes. Suppose you had an {@link ObservableList} of Numbers
246 * to display in a ListView and wanted to color all of the negative values red
247 * and all positive or 0 values black.
248 * One way to achieve this is with a custom cellFactory which changes the
249 * styleClass of the Cell based on whether the value is negative or positive. This
250 * is as simple as adding code to test if the number in the cell is negative,
251 * and adding a "negative" styleClass. If the number is not negative, the "negative"
252 * string should be removed. This approach allows for the colors to be defined
253 * from CSS, allowing for simple customization. The CSS file would then include
254 * something like the following:
255 *
256 * <pre>
257 * .list-cell {
258 * -fx-text-fill: black;
259 * }
260 *
261 * .list-cell .negative {
262 * -fx-text-fill: red;
263 * }</pre>
264 *
265 * <h3>Editing</h3>
266 * <p>Most virtualized controls that use the Cell architecture (e.g. {@link ListView},
267 * {@link TreeView}, {@link TableView} and {@link TreeTableView}) all support
268 * the notion of editing values directly via the cell. You can learn more about
269 * the control-specific details by going to the 'editing' section in the class
270 * documentation for the controls linked above. The remainder of this section
271 * will cover some of the finer details of editing with cells.</p>
272 *
273 * <p>The general flow of editing is as follows (note that in these steps the
274 * {@link ListView} control is used as an example, but similar API exists for
275 * all controls mentioned above, and the process is exactly the same in general):</p>
276 *
277 * <ol>
278 * <li>User requests a cell enter editing mode (via keyboard or mouse commands),
279 * or the developer requests that a cell enter editing mode (by calling a
280 * method such as the ListView {@link ListView#edit(int) edit} method.
281 * <strong>Note:</strong> If the user double-clicks or fires an appropriate
282 * keyboard command to initiate editing, then they are effectively calling
283 * the appropriate edit method on the control (i.e. the entry method for
284 * user-initiated and developer-initiated editing is the same).</li>
285 * <li>Each cell in the visible region of the control is notified that the
286 * current {@link javafx.scene.control.ListView#editingIndexProperty() editing cell}
287 * has changed, and checks to see if it is itself. At this point one of three
288 * things can happen:
289 * <ol>
290 * <li>If the editing index is the same index as the cell,
291 * {@link #startEdit()} will be called on this cell. Some pointers:
292 * <ol>
293 * <li>It is recommended that subclasses of Cell override the {@link #startEdit()}
294 * method to update the visuals of the cell when enters the editing state. Note
295 * however that it is very important that subclasses that override the
296 * {@link #startEdit()} method continue to call {@code super.startEdit()} so
297 * that parent classes can update additional state that is necessary for
298 * editing to be successful.</li>
299 * <li>Within the {@link #startEdit()} method is an ideal
300 * time to change the visuals of the cell. For example (and
301 * note that this example is more fleshed out in the UI control
302 * javadocs for {@link ListView}, etc), you may set the
303 * {@link #graphicProperty()} of the cell to a
304 * {@link TextField} and set the {@link #textProperty()}
305 * to null. This would allow end users to then type in input
306 * and make changes to your data model.</li>
307 * <li>When the user has completed editing, they will want
308 * to commit or cancel their change. This is your responsibility
309 * to handle (e.g. by having the Enter key
310 * {@link #commitEdit(Object) commit the edit}
311 * and the ESC key {@link #cancelEdit() cancel the edit}).
312 * You do this by attaching the appropriate event listeners
313 * to the nodes you show whilst in the editing state.</li>
314 * </ol>
315 * </li>
316 * <li>If the editing index is not the same index as the cell, and
317 * if the cell is currently in the {@link #isEditing() editing state},
318 * {@link #cancelEdit()} will be called on this cell. As with the
319 * {@link #startEdit()} method, you should override this method to
320 * clean up the visuals of the cell (and most probably return the
321 * {@link #graphicProperty()} back to null and set the
322 * {@link #textProperty()} to its (possibly new) value. Again,
323 * be sure to always call {@code super.cancelEdit()} to make sure all
324 * state is correctly updated.</li>
325 * <li>If the editing index is not the same index as the cell, and
326 * if the cell is not currently in the {@link #isEditing()} editing state},
327 * then nothing will happen on this cell.</li>
328 * </ol>
329 * </li>
330 * </ol>
331 *
332 *
333 * @param <T> The type of the item contained within the Cell.
334 *
335 * @since JavaFX 2.0
336 */
337 public class Cell<T> extends Labeled {
338
339 /***************************************************************************
340 * *
341 * Constructors *
342 * *
343 **************************************************************************/
344
345 /**
346 * Creates a default Cell with the default style class of 'cell'.
347 */
348 public Cell() {
349 setText(null); // default to null text, to match the null item
350 // focusTraversable is styleable through css. Calling setFocusTraversable
351 // makes it look to css like the user set the value and css will not
352 // override. Initializing focusTraversable by calling set on the
353 // CssMetaData ensures that css will be able to override the value.
354 ((StyleableProperty<Boolean>)(WritableValue<Boolean>)focusTraversableProperty()).applyStyle(null, Boolean.FALSE);
355 getStyleClass().addAll(DEFAULT_STYLE_CLASS);
356
357 /**
358 * Indicates whether or not this cell has focus. For example, a
359 * ListView defines zero or one cell as being the "focused" cell. This cell
360 * would have focused set to true.
361 */
362 super.focusedProperty().addListener(new InvalidationListener() {
363 @Override public void invalidated(Observable property) {
364 pseudoClassStateChanged(PSEUDO_CLASS_FOCUSED, isFocused()); // TODO is this necessary??
365
366 // The user has shifted focus, so we should cancel the editing on this cell
367 if (!isFocused() && isEditing()) {
368 cancelEdit();
369 }
370 }
371 });
372
373 // initialize default pseudo-class state
374 pseudoClassStateChanged(PSEUDO_CLASS_EMPTY, true);
375 }
376
377
378
379 /***************************************************************************
380 * *
381 * Properties *
382 * *
383 **************************************************************************/
384
385 // --- item
386 private ObjectProperty<T> item = new SimpleObjectProperty<T>(this, "item");
387
388 /**
389 * The data value associated with this Cell. This value is set by the
390 * virtualized Control when the Cell is created or updated. This represents
391 * the raw data value.
392 *
393 * <p>This value should only be set in subclasses of Cell by the virtualised
394 * user interface controls that know how to properly work with the Cell
395 * class.
396 * @return the data value associated with this cell
397 */
398 public final ObjectProperty<T> itemProperty() { return item; }
399
400 /**
401 * Sets the item to the given value - should not be called directly as the
402 * item is managed by the virtualized control.
403 * @param value the new data value to set in this cell
404 */
405 public final void setItem(T value) { item.set(value); }
406
407 /**
408 * Returns the data value associated with this Cell.
409 * @return the data value associated with this cell
410 */
411 public final T getItem() { return item.get(); }
412
413
414
415 // --- empty
416 private ReadOnlyBooleanWrapper empty = new ReadOnlyBooleanWrapper(true) {
417 @Override protected void invalidated() {
418 final boolean active = get();
419 pseudoClassStateChanged(PSEUDO_CLASS_EMPTY, active);
420 pseudoClassStateChanged(PSEUDO_CLASS_FILLED, !active);
421 }
422
423 @Override
424 public Object getBean() {
425 return Cell.this;
426 }
427
428 @Override
429 public String getName() {
430 return "empty";
431 }
432 };
433
434 /**
435 * A property used to represent whether the cell has any contents.
436 * If true, then the Cell contains no data and is not associated with any
437 * data item in the virtualized Control.
438 *
439 * <p>When a cell is empty, it can be styled differently via the 'empty'
440 * CSS pseudo class state. For example, it may not receive any
441 * alternate row highlighting, or it may not receive hover background
442 * fill when hovered.
443 * @return the representation of whether this cell has any contents
444 */
445 public final ReadOnlyBooleanProperty emptyProperty() { return empty.getReadOnlyProperty(); }
446
447 private void setEmpty(boolean value) { empty.set(value); }
448
449 /**
450 * Returns a boolean representing whether the cell is considered to be empty
451 * or not.
452 * @return true if cell is empty, otherwise false
453 */
454 public final boolean isEmpty() { return empty.get(); }
455
456
457
458 // --- selected
459 private ReadOnlyBooleanWrapper selected = new ReadOnlyBooleanWrapper() {
460 @Override protected void invalidated() {
461 pseudoClassStateChanged(PSEUDO_CLASS_SELECTED, get());
462 }
463
464 @Override
465 public Object getBean() {
466 return Cell.this;
467 }
468
469 @Override
470 public String getName() {
471 return "selected";
472 }
473 };
474
475 /**
476 * Indicates whether or not this cell has been selected. For example, a
477 * ListView defines zero or more cells as being the "selected" cells.
478 * @return the representation of whether this cell has been selected
479 */
480 public final ReadOnlyBooleanProperty selectedProperty() { return selected.getReadOnlyProperty(); }
481
482 void setSelected(boolean value) { selected.set(value); }
483
484 /**
485 * Returns whether this cell is currently selected or not.
486 * @return True if the cell is selected, false otherwise.
487 */
488 public final boolean isSelected() { return selected.get(); }
489
490
491
492 // --- Editing
493 private ReadOnlyBooleanWrapper editing;
494
495 private void setEditing(boolean value) {
496 editingPropertyImpl().set(value);
497 }
498
499 /**
500 * Represents whether the cell is currently in its editing state or not.
501 * @return true if this cell is currently in its editing state, otherwise
502 * false
503 */
504 public final boolean isEditing() {
505 return editing == null ? false : editing.get();
506 }
507
508 /**
509 * Property representing whether this cell is currently in its editing state.
510 * @return the representation of whether this cell is currently in its
511 * editing state
512 */
513 public final ReadOnlyBooleanProperty editingProperty() {
514 return editingPropertyImpl().getReadOnlyProperty();
515 }
516
517 private ReadOnlyBooleanWrapper editingPropertyImpl() {
518 if (editing == null) {
519 editing = new ReadOnlyBooleanWrapper(this, "editing");
520 }
521 return editing;
522 }
523
524
525
526 // --- Editable
527 private BooleanProperty editable;
528
529 /**
530 * Allows for certain cells to not be able to be edited. This is useful in
531 * cases where, say, a List has 'header rows' - it does not make sense for
532 * the header rows to be editable, so they should have editable set to
533 * false.
534 *
535 * @param value A boolean representing whether the cell is editable or not.
536 * If true, the cell is editable, and if it is false, the cell can not
537 * be edited.
538 */
539 public final void setEditable(boolean value) {
540 editableProperty().set(value);
541 }
542
543 /**
544 * Returns whether this cell is allowed to be put into an editing state.
545 * @return true if this cell is allowed to be put into an editing state,
546 * otherwise false
547 */
548 public final boolean isEditable() {
549 return editable == null ? true : editable.get();
550 }
551
552 /**
553 * A property representing whether this cell is allowed to be put into an
554 * editing state. By default editable is set to true in Cells (although for
555 * a subclass of Cell to be allowed to enter its editing state, it may have
556 * to satisfy additional criteria. For example, ListCell requires that the
557 * ListView {@link ListView#editableProperty() editable} property is also
558 * true.
559 * @return the representation of whether this cell is allowed to be put into
560 * an editing state
561 */
562 public final BooleanProperty editableProperty() {
563 if (editable == null) {
564 editable = new SimpleBooleanProperty(this, "editable", true);
565 }
566 return editable;
567 }
568
569
570
571 /***************************************************************************
572 * *
573 * Public API *
574 * *
575 **************************************************************************/
576
577 /**
578 * Call this function to transition from a non-editing state into an editing
579 * state, if the cell is editable. If this cell is already in an editing
580 * state, it will stay in it.
581 */
582 public void startEdit() {
583 if (isEditable() && !isEditing() && !isEmpty()) {
584 setEditing(true);
585 }
586 }
587
588 /**
589 * Call this function to transition from an editing state into a non-editing
590 * state, without saving any user input.
591 */
592 public void cancelEdit() {
593 if (isEditing()) {
594 setEditing(false);
595 }
596 }
597
598 /**
599 * Call this function when appropriate (based on the user interaction requirements
600 * of your cell editing user interface) to do two things:
601 *
602 * <ol>
603 * <li>Fire the appropriate events back to the backing UI control (e.g.
604 * {@link ListView}). This will begin the process of pushing this edit
605 * back to the relevant data source / property (although it does not
606 * guarantee that this will be successful - that is dependent upon the
607 * specific edit commit handler being used). Refer to the UI control
608 * class javadoc for more detail.</li>
609 * <li>Begin the transition from an editing state into a non-editing state.</li>
610 * </ol>
611 *
612 * <p>In general there is no need to override this method in custom cell
613 * implementations - it should be sufficient to simply call this method
614 * when appropriate (e.g. when the user pressed the Enter key, you may do something
615 * like {@code cell.commitEdit(converter.fromString(textField.getText()));}</p>
616 *
617 * @param newValue The value as input by the end user, which should be
618 * persisted in the relevant way given the data source underpinning the
619 * user interface and the install edit commit handler of the UI control.
620 */
621 public void commitEdit(T newValue) {
622 if (isEditing()) {
623 setEditing(false);
624 }
625 }
626
627 /** {@inheritDoc} */
628 @Override protected void layoutChildren() {
629 if (itemDirty) {
630 updateItem(getItem(), isEmpty());
631 itemDirty = false;
632 }
633 super.layoutChildren();
634 }
635
636
637
638 /***************************************************************************
639 * *
640 * Expert API *
641 * *
642 **************************************************************************/
643
644 /**
645 * The updateItem method should not be called by developers, but it is the
646 * best method for developers to override to allow for them to customise the
647 * visuals of the cell. To clarify, developers should never call this method
648 * in their code (they should leave it up to the UI control, such as the
649 * {@link javafx.scene.control.ListView} control) to call this method. However,
650 * the purpose of having the updateItem method is so that developers, when
651 * specifying custom cell factories (again, like the ListView
652 * {@link javafx.scene.control.ListView#cellFactoryProperty() cell factory}),
653 * the updateItem method can be overridden to allow for complete customisation
654 * of the cell.
655 *
656 * <p>It is <strong>very important</strong> that subclasses
657 * of Cell override the updateItem method properly, as failure to do so will
658 * lead to issues such as blank cells or cells with unexpected content
659 * appearing within them. Here is an example of how to properly override the
660 * updateItem method:
661 *
662 * <pre>
663 * protected void updateItem(T item, boolean empty) {
664 * super.updateItem(item, empty);
665 *
666 * if (empty || item == null) {
667 * setText(null);
668 * setGraphic(null);
669 * } else {
670 * setText(item.toString());
671 * }
672 * }
673 * </pre>
674 *
675 * <p>Note in this code sample two important points:
676 * <ol>
677 * <li>We call the super.updateItem(T, boolean) method. If this is not
678 * done, the item and empty properties are not correctly set, and you are
679 * likely to end up with graphical issues.</li>
680 * <li>We test for the <code>empty</code> condition, and if true, we
681 * set the text and graphic properties to null. If we do not do this,
682 * it is almost guaranteed that end users will see graphical artifacts
683 * in cells unexpectedly.</li>
684 * </ol>
685 *
686 * @param item The new item for the cell.
687 * @param empty whether or not this cell represents data from the list. If it
688 * is empty, then it does not represent any domain data, but is a cell
689 * being used to render an "empty" row.
690 */
691 protected void updateItem(T item, boolean empty) {
692 setItem(item);
693 setEmpty(empty);
694 if (empty && isSelected()) {
695 updateSelected(false);
696 }
697 }
698
699 /**
700 * Updates whether this cell is in a selected state or not.
701 * @param selected whether or not to select this cell.
702 */
703 public void updateSelected(boolean selected) {
704 if (selected && isEmpty()) return;
705 boolean wasSelected = isSelected();
706 setSelected(selected);
707
708 if (wasSelected != selected) {
709 markCellDirty();
710 }
711 }
712
713 /**
714 * This method is called by Cell subclasses so that certain CPU-intensive
715 * actions (specifically, calling {@link #updateItem(Object, boolean)}) are
716 * only performed when necessary (that is, they are only performed
717 * when the currently set {@link #itemProperty() item} is considered to be
718 * different than the proposed new item that could be set).
719 *
720 * <p>The default implementation of this method tests against equality, but
721 * developers are able to override this method to perform checks in other ways
722 * that are specific to their domain.</p>
723 *
724 * @param oldItem The currently-set item contained within the cell (i.e. it is
725 * the same as what is available via {@link #getItem()}).
726 * @param newItem The item that will be set in the cell, if this method
727 * returns true. If this method returns false, it may not be
728 * set.
729 * @return Returns true if the new item is considered to be different than
730 * the old item. By default this method tests against equality, but
731 * subclasses may alter the implementation to test appropriate to
732 * their needs.
733 * @since JavaFX 8u40
734 */
735 protected boolean isItemChanged(T oldItem, T newItem) {
736 return oldItem != null ? !oldItem.equals(newItem) : newItem != null;
737 }
738
739
740
741 /***************************************************************************
742 * *
743 * Private Implementation *
744 * *
745 **************************************************************************/
746
747 // itemDirty and markCellDirty introduced as a solution for JDK-8145588.
748 // In the fullness of time, a more fully developed solution can be developed
749 // that offers a public API around this lazy-dirty impl.
750 private boolean itemDirty = false;
751 private final void markCellDirty() {
752 itemDirty = true;
753 requestLayout();
754 }
755
756
757 /***************************************************************************
758 * *
759 * Stylesheet Handling *
760 * *
761 **************************************************************************/
762
763 private static final String DEFAULT_STYLE_CLASS = "cell";
764 private static final PseudoClass PSEUDO_CLASS_SELECTED =
765 PseudoClass.getPseudoClass("selected");
766 private static final PseudoClass PSEUDO_CLASS_FOCUSED =
767 PseudoClass.getPseudoClass("focused");
768 private static final PseudoClass PSEUDO_CLASS_EMPTY =
769 PseudoClass.getPseudoClass("empty");
770 private static final PseudoClass PSEUDO_CLASS_FILLED =
771 PseudoClass.getPseudoClass("filled");
772
773 /**
774 * Returns the initial focus traversable state of this control, for use
775 * by the JavaFX CSS engine to correctly set its initial value. This method
776 * is overridden as by default UI controls have focus traversable set to true,
777 * but that is not appropriate for this control.
778 *
779 * @since 9
780 */
781 @Override protected Boolean getInitialFocusTraversable() {
782 return Boolean.FALSE;
783 }
784 }