1 /* 2 * Copyright (c) 2010, 2016, 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 */ 397 public final ObjectProperty<T> itemProperty() { return item; } 398 399 /** 400 * Sets the item to the given value - should not be called directly as the 401 * item is managed by the virtualized control. 402 */ 403 public final void setItem(T value) { item.set(value); } 404 405 /** 406 * Returns the data value associated with this Cell. 407 */ 408 public final T getItem() { return item.get(); } 409 410 411 412 // --- empty 413 private ReadOnlyBooleanWrapper empty = new ReadOnlyBooleanWrapper(true) { 414 @Override protected void invalidated() { 415 final boolean active = get(); 416 pseudoClassStateChanged(PSEUDO_CLASS_EMPTY, active); 417 pseudoClassStateChanged(PSEUDO_CLASS_FILLED, !active); 418 } 419 420 @Override 421 public Object getBean() { 422 return Cell.this; 423 } 424 425 @Override 426 public String getName() { 427 return "empty"; 428 } 429 }; 430 431 /** 432 * A property used to represent whether the cell has any contents. 433 * If true, then the Cell contains no data and is not associated with any 434 * data item in the virtualized Control. 435 * 436 * <p>When a cell is empty, it can be styled differently via the 'empty' 437 * CSS pseudo class state. For example, it may not receive any 438 * alternate row highlighting, or it may not receive hover background 439 * fill when hovered. 440 */ 441 public final ReadOnlyBooleanProperty emptyProperty() { return empty.getReadOnlyProperty(); } 442 443 private void setEmpty(boolean value) { empty.set(value); } 444 445 /** 446 * Returns a boolean representing whether the cell is considered to be empty 447 * or not. 448 */ 449 public final boolean isEmpty() { return empty.get(); } 450 451 452 453 // --- selected 454 private ReadOnlyBooleanWrapper selected = new ReadOnlyBooleanWrapper() { 455 @Override protected void invalidated() { 456 pseudoClassStateChanged(PSEUDO_CLASS_SELECTED, get()); 457 } 458 459 @Override 460 public Object getBean() { 461 return Cell.this; 462 } 463 464 @Override 465 public String getName() { 466 return "selected"; 467 } 468 }; 469 470 /** 471 * Indicates whether or not this cell has been selected. For example, a 472 * ListView defines zero or more cells as being the "selected" cells. 473 */ 474 public final ReadOnlyBooleanProperty selectedProperty() { return selected.getReadOnlyProperty(); } 475 476 void setSelected(boolean value) { selected.set(value); } 477 478 /** 479 * Returns whether this cell is currently selected or not. 480 * @return True if the cell is selected, false otherwise. 481 */ 482 public final boolean isSelected() { return selected.get(); } 483 484 485 486 // --- Editing 487 private ReadOnlyBooleanWrapper editing; 488 489 private void setEditing(boolean value) { 490 editingPropertyImpl().set(value); 491 } 492 493 /** 494 * Represents whether the cell is currently in its editing state or not. 495 */ 496 public final boolean isEditing() { 497 return editing == null ? false : editing.get(); 498 } 499 500 /** 501 * Property representing whether this cell is currently in its editing state. 502 */ 503 public final ReadOnlyBooleanProperty editingProperty() { 504 return editingPropertyImpl().getReadOnlyProperty(); 505 } 506 507 private ReadOnlyBooleanWrapper editingPropertyImpl() { 508 if (editing == null) { 509 editing = new ReadOnlyBooleanWrapper(this, "editing"); 510 } 511 return editing; 512 } 513 514 515 516 // --- Editable 517 private BooleanProperty editable; 518 519 /** 520 * Allows for certain cells to not be able to be edited. This is useful in 521 * cases where, say, a List has 'header rows' - it does not make sense for 522 * the header rows to be editable, so they should have editable set to 523 * false. 524 * 525 * @param value A boolean representing whether the cell is editable or not. 526 * If true, the cell is editable, and if it is false, the cell can not 527 * be edited. 528 */ 529 public final void setEditable(boolean value) { 530 editableProperty().set(value); 531 } 532 533 /** 534 * Returns whether this cell is allowed to be put into an editing state. 535 */ 536 public final boolean isEditable() { 537 return editable == null ? true : editable.get(); 538 } 539 540 /** 541 * A property representing whether this cell is allowed to be put into an 542 * editing state. By default editable is set to true in Cells (although for 543 * a subclass of Cell to be allowed to enter its editing state, it may have 544 * to satisfy additional criteria. For example, ListCell requires that the 545 * ListView {@link ListView#editableProperty() editable} property is also 546 * true. 547 */ 548 public final BooleanProperty editableProperty() { 549 if (editable == null) { 550 editable = new SimpleBooleanProperty(this, "editable", true); 551 } 552 return editable; 553 } 554 555 556 557 /*************************************************************************** 558 * * 559 * Public API * 560 * * 561 **************************************************************************/ 562 563 /** 564 * Call this function to transition from a non-editing state into an editing 565 * state, if the cell is editable. If this cell is already in an editing 566 * state, it will stay in it. 567 */ 568 public void startEdit() { 569 if (isEditable() && !isEditing() && !isEmpty()) { 570 setEditing(true); 571 } 572 } 573 574 /** 575 * Call this function to transition from an editing state into a non-editing 576 * state, without saving any user input. 577 */ 578 public void cancelEdit() { 579 if (isEditing()) { 580 setEditing(false); 581 } 582 } 583 584 /** 585 * Call this function when appropriate (based on the user interaction requirements 586 * of your cell editing user interface) to do two things: 587 * 588 * <ol> 589 * <li>Fire the appropriate events back to the backing UI control (e.g. 590 * {@link ListView}). This will begin the process of pushing this edit 591 * back to the relevant data source / property (although it does not 592 * guarantee that this will be successful - that is dependent upon the 593 * specific edit commit handler being used). Refer to the UI control 594 * class javadoc for more detail.</li> 595 * <li>Begin the transition from an editing state into a non-editing state.</li> 596 * </ol> 597 * 598 * <p>In general there is no need to override this method in custom cell 599 * implementations - it should be sufficient to simply call this method 600 * when appropriate (e.g. when the user pressed the Enter key, you may do something 601 * like {@code cell.commitEdit(converter.fromString(textField.getText()));}</p> 602 * 603 * @param newValue The value as input by the end user, which should be 604 * persisted in the relevant way given the data source underpinning the 605 * user interface and the install edit commit handler of the UI control. 606 */ 607 public void commitEdit(T newValue) { 608 if (isEditing()) { 609 setEditing(false); 610 } 611 } 612 613 /** {@inheritDoc} */ 614 @Override protected void layoutChildren() { 615 if (itemDirty) { 616 updateItem(getItem(), isEmpty()); 617 itemDirty = false; 618 } 619 super.layoutChildren(); 620 } 621 622 623 624 /*************************************************************************** 625 * * 626 * Expert API * 627 * * 628 **************************************************************************/ 629 630 /** 631 * The updateItem method should not be called by developers, but it is the 632 * best method for developers to override to allow for them to customise the 633 * visuals of the cell. To clarify, developers should never call this method 634 * in their code (they should leave it up to the UI control, such as the 635 * {@link javafx.scene.control.ListView} control) to call this method. However, 636 * the purpose of having the updateItem method is so that developers, when 637 * specifying custom cell factories (again, like the ListView 638 * {@link javafx.scene.control.ListView#cellFactoryProperty() cell factory}), 639 * the updateItem method can be overridden to allow for complete customisation 640 * of the cell. 641 * 642 * <p>It is <strong>very important</strong> that subclasses 643 * of Cell override the updateItem method properly, as failure to do so will 644 * lead to issues such as blank cells or cells with unexpected content 645 * appearing within them. Here is an example of how to properly override the 646 * updateItem method: 647 * 648 * <pre> 649 * protected void updateItem(T item, boolean empty) { 650 * super.updateItem(item, empty); 651 * 652 * if (empty || item == null) { 653 * setText(null); 654 * setGraphic(null); 655 * } else { 656 * setText(item.toString()); 657 * } 658 * } 659 * </pre> 660 * 661 * <p>Note in this code sample two important points: 662 * <ol> 663 * <li>We call the super.updateItem(T, boolean) method. If this is not 664 * done, the item and empty properties are not correctly set, and you are 665 * likely to end up with graphical issues.</li> 666 * <li>We test for the <code>empty</code> condition, and if true, we 667 * set the text and graphic properties to null. If we do not do this, 668 * it is almost guaranteed that end users will see graphical artifacts 669 * in cells unexpectedly.</li> 670 * </ol> 671 * 672 * @param item The new item for the cell. 673 * @param empty whether or not this cell represents data from the list. If it 674 * is empty, then it does not represent any domain data, but is a cell 675 * being used to render an "empty" row. 676 * @expert 677 */ 678 protected void updateItem(T item, boolean empty) { 679 setItem(item); 680 setEmpty(empty); 681 if (empty && isSelected()) { 682 updateSelected(false); 683 } 684 } 685 686 /** 687 * Updates whether this cell is in a selected state or not. 688 * @expert 689 * @param selected whether or not to select this cell. 690 */ 691 public void updateSelected(boolean selected) { 692 if (selected && isEmpty()) return; 693 boolean wasSelected = isSelected(); 694 setSelected(selected); 695 696 if (wasSelected != selected) { 697 markCellDirty(); 698 } 699 } 700 701 /** 702 * This method is called by Cell subclasses so that certain CPU-intensive 703 * actions (specifically, calling {@link #updateItem(Object, boolean)}) are 704 * only performed when necessary (that is, they are only performed 705 * when the currently set {@link #itemProperty() item} is considered to be 706 * different than the proposed new item that could be set). 707 * 708 * <p>The default implementation of this method tests against equality, but 709 * developers are able to override this method to perform checks in other ways 710 * that are specific to their domain.</p> 711 * 712 * @param oldItem The currently-set item contained within the cell (i.e. it is 713 * the same as what is available via {@link #getItem()}). 714 * @param newItem The item that will be set in the cell, if this method 715 * returns true. If this method returns false, it may not be 716 * set. 717 * @return Returns true if the new item is considered to be different than 718 * the old item. By default this method tests against equality, but 719 * subclasses may alter the implementation to test appropriate to 720 * their needs. 721 * @since JavaFX 8u40 722 */ 723 protected boolean isItemChanged(T oldItem, T newItem) { 724 return oldItem != null ? !oldItem.equals(newItem) : newItem != null; 725 } 726 727 728 729 /*************************************************************************** 730 * * 731 * Private Implementation * 732 * * 733 **************************************************************************/ 734 735 // itemDirty and markCellDirty introduced as a solution for JDK-8145588. 736 // In the fullness of time, a more fully developed solution can be developed 737 // that offers a public API around this lazy-dirty impl. 738 private boolean itemDirty = false; 739 private final void markCellDirty() { 740 itemDirty = true; 741 requestLayout(); 742 } 743 744 745 /*************************************************************************** 746 * * 747 * Stylesheet Handling * 748 * * 749 **************************************************************************/ 750 751 private static final String DEFAULT_STYLE_CLASS = "cell"; 752 private static final PseudoClass PSEUDO_CLASS_SELECTED = 753 PseudoClass.getPseudoClass("selected"); 754 private static final PseudoClass PSEUDO_CLASS_FOCUSED = 755 PseudoClass.getPseudoClass("focused"); 756 private static final PseudoClass PSEUDO_CLASS_EMPTY = 757 PseudoClass.getPseudoClass("empty"); 758 private static final PseudoClass PSEUDO_CLASS_FILLED = 759 PseudoClass.getPseudoClass("filled"); 760 761 /** 762 * Returns the initial focus traversable state of this control, for use 763 * by the JavaFX CSS engine to correctly set its initial value. This method 764 * is overridden as by default UI controls have focus traversable set to true, 765 * but that is not appropriate for this control. 766 * 767 * @since 9 768 */ 769 @Override protected Boolean getInitialFocusTraversable() { 770 return Boolean.FALSE; 771 } 772 }