Last modified by cds on 2025/01/30 12:03
<
From version < 21.1 >
edited by cds
on 2012/10/24 13:33
To version < 23.1 >
edited by cds
on 2012/10/24 17:31
>
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139 139  
140 140  {{code language="java"}}
141 141  Table table = new Table(parent, SWT.BORDER);
142 +table.setHeaderVisible(true);
142 142  TableColumn column = new TableColumn(table, SWT.NONE);
143 143  column.setWidth(80);
145 +column.setText("Tape Data");
144 144  tableViewer = new TableViewer(table);
145 145  {{/code}}
146 146  )))
... ... @@ -340,8 +340,216 @@
340 340  
341 341  = Creating an Extension Point =
342 342  
343 -WRITE THIS SECTION
345 +For the final part of the tutorial, we will now use the extension point mechanism of Eclipse to add some behavior to our Turing Machines. An //extension point// is basically a well-defined point where other plug-ins can register to add functionality. The extension point is basically defined by an XML Schema file that defines an interface; other plug-ins may access this interface using XML code in their {{code language="none"}}plugin.xml{{/code}} file, so-called //extensions//. Our extension point will provide an interface for classes that define behavior of a Turing Machine, and we will call them head controllers (programs that control the tape head).
344 344  
347 +== Defining a Command Class ==
348 +
349 +We will start by defining a class representing a command that will be passed to a selected head controller.
350 +
351 +1. Add a class {{code language="none"}}HeadCommand{{/code}} to the package {{code language="none"}}de.cau.cs.rtprak.login.simple.controller{{/code}}.
352 +1. Add a nested public static enumeration {{code language="none"}}Action{{/code}} with values {{code language="none"}}WRITE{{/code}}, {{code language="none"}}ERASE{{/code}}, and {{code language="none"}}NULL{{/code}}.
353 +1. Add a nested public static enumeration {{code language="none"}}Direction{{/code}} with values {{code language="none"}}LEFT{{/code}}, {{code language="none"}}RIGHT{{/code}}, and {{code language="none"}}NONE{{/code}}.
354 +1. (((
355 +Add the following private fields:
356 +
357 +{{code language="java"}}
358 +private Action action;
359 +private Direction direction;
360 +private char newChar;
361 +{{/code}}
362 +)))
363 +1. Add a constructor to initialize the fields.
364 +1. Add getter methods to access the fields.
365 +
366 +== Defining the Controller Interface ==
367 +
368 +We will now define an interface that all head controllers will have to implement:
369 +
370 +1. Add an interface {{code language="none"}}IHeadController{{/code}} in the package {{code language="none"}}de.cau.cs.rtprak.login.simple.controller{{/code}}.
371 +1. (((
372 +Add the following methods to the interface:
373 +
374 +{{code language="java"}}
375 +/**
376 + * Calculate the next command depending on the currently seen character.
377 + * @param character the currently seen character
378 + * @return the next command specifying which character to write and
379 + * which direction to move the head
380 + */
381 +HeadCommand nextCommand(char character);
382 +
383 +/**
384 + * Reset the internal state of the head controller.
385 + */
386 +void reset();
387 +{{/code}}
388 +)))
389 +
390 +== Defining the Extension Point ==
391 +
392 +We will now define the extension point that head controllers will be registered at.
393 +
394 +1. Open the {{code language="none"}}plugin.xml{{/code}} file in the //Plugin Manifest Editor// and switch to the //Extension Points// tab.
395 +1. Click the //Add// button and enter {{code language="none"}}de.cau.cs.rtprak.login.simple.headControllers{{/code}} as the extension point's ID, and {{code language="none"}}Head Controllers{{/code}} as its name. Shorten the schema file's file name to {{code language="none"}}schema/headControllers.exsd{{/code}}. Make sure that //Edit extension point schema when done// is checked and click //Finish//.
396 +1. Eclipse will now have opened the new schema file in the //Extension Point Schema Editor//, a graphical editor similar to the //Plugin Manifest Editor// that provides a way to define things that might be easier than directly editing the text files.
397 +1. In the new editor, open the //Definition// tab.
398 +1. Add a new element named {{code language="none"}}controller{{/code}}.
399 +1. Add three new attributes to the {{code language="none"}}controller{{/code}} element:\\
400 +1*. First attribute: name {{code language="none"}}id{{/code}}, use {{code language="none"}}required{{/code}}, type {{code language="none"}}string{{/code}}, translatable {{code language="none"}}false{{/code}}.
401 +1*. Second attribute: name {{code language="none"}}name{{/code}}, use {{code language="none"}}required{{/code}}, type {{code language="none"}}string{{/code}}, translatable {{code language="none"}}true{{/code}}.
402 +1*. Third attribute: name {{code language="none"}}class{{/code}}, use {{code language="none"}}required{{/code}}, type {{code language="none"}}java{{/code}}, implements {{code language="none"}}de.cau.cs.rtprak.login.simple.controller.IHeadController{{/code}}. This is the attribute that will tell us which Java class actually implements the controller that is to be registered at our extension point. To make sure that we know how to speak to the class, we require it to implement the interface we defined for head controllers.
403 +1. Add a sequence to the {{code language="none"}}extension{{/code}} element. Right-click the sequence and click //New// -> //controller//. Set the //Min Occurrences// of the sequence to 0, and set //Max Occurrences// to be //Unbounded//.
404 +1. Save the editor and switch back to the //Plugin Manifest Editor//.
405 +1. On the Runtime tab, add {{code language="none"}}de.cau.cs.rtprak.login.simple.controller{{/code}} to the list of packages exported by the plug-in. This is necessary because plug-ins that want to provide extensions for the extension point must provide a class that implements {{code language="none"}}IHeadController{{/code}}. For this to work, those plug-ins must have access to that interface; thus, we have to export the package containing it.
406 +
407 +== Accessing the Extension Point ==
408 +
409 +We will now add a class that will be in charge of loading all extensions registered at our new extension point.
410 +
411 +1. (((
412 +Add a class {{code language="none"}}HeadControllers{{/code}} to the package {{code language="none"}}de.cau.cs.rtprak.login.simple.controller{{/code}}. Add the following code:
413 +
414 +{{code language="java"}}
415 +/**
416 + * Class that gathers extension data from the 'headControllers' extension point
417 + * and publishes this data using the singleton pattern.
418 + * @author msp
419 + */
420 +public class HeadControllers {
421 + /** Identifier of the extension point */
422 + public final static String EXTENSION_POINT_ID = "de.cau.cs.rtprak.groupx.simple.headControllers";
423 + /** The singleton instance of the {@code HeadControllers} class */
424 + public final static HeadControllers INSTANCE = new HeadControllers();
425 + /** list of head controller ids with associated names. */
426 + private List<String[]> controllerNames = new LinkedList<String[]>();
427 + /** map of controller ids to their runtime instances. */
428 + private Map<String, IHeadController> controllerMap = new HashMap<String, IHeadController>();
429 + /**
430 + * Creates an instance of this class and gathers extension data.
431 + */
432 + HeadControllers() {
433 + IConfigurationElement[] elements = Platform.getExtensionRegistry()
434 + .getConfigurationElementsFor(EXTENSION_POINT_ID);
435 + for (IConfigurationElement element : elements) {
436 + if ("controller".equals(element.getName())) {
437 + String id = element.getAttribute("id");
438 + String name = element.getAttribute("name");
439 + if (id != null && name != null) {
440 + try {
441 + IHeadController controller = (IHeadController)element
442 + .createExecutableExtension("class");
443 + controllerNames.add(new String[] {id, name});
444 + controllerMap.put(id, controller);
445 + }
446 + catch (CoreException exception) {
447 + StatusManager.getManager().handle(exception, Activator.PLUGIN_ID);
448 + }
449 + }
450 + }
451 + }
452 + }
453 +
454 + /**
455 + * Returns a list of controller ids and names. The arrays in the list are
456 + * all of size 2: the first element is an id, and the second element is the
457 + * associated name. The controller name is a user-friendly string to be
458 + * displayed in the UI.
459 + * @return a list of controller ids and names
460 + */
461 + public List<String[]> getControllerNames() {
462 + return controllerNames;
463 + }
464 +
465 + /**
466 + * Returns the head controller instance for the given id.
467 + * @param id identifier of a head controller
468 + * @return the associated controller
469 + */
470 + public IHeadController getController(final String id) {
471 + return controllerMap.get(id);
472 + }
473 +}
474 +{{/code}}
475 +)))
476 +
477 +== Adding Support for Head Controllers to the View ==
478 +
479 +We will now have to add support for head controllers to our view.
480 +
481 +1. Open the {{code language="none"}}TapeViewPart{{/code}} class and add the private fields {{code language="none"}}checkedControllerAction{{/code}} of type [[IAction>>url:http://help.eclipse.org/juno/topic/org.eclipse.platform.doc.isv/reference/api/org/eclipse/jface/action/IAction.html||shape="rect"]] and {{code language="none"}}currentController{{/code}} of type {{code language="none"}}IHeadController{{/code}}.
482 +1. (((
483 +Add a list of registered head controllers to the view's menu (which can be opened using the small white triangle) in the {{code language="none"}}createPartControl(){{/code}} method:
484 +
485 +{{code language="java"}}
486 +IMenuManager menuManager = getViewSite().getActionBars().getMenuManager();
487 +for (String[] controllerName : HeadControllers.INSTANCE.getControllerNames()) {
488 + final String id = controllerName[0];
489 + String name = controllerName[1];
490 + Action action = new Action(name, IAction.AS_RADIO_BUTTON) {
491 + public void run() {
492 + if (checkedControllerAction != null) {
493 + checkedControllerAction.setChecked(false);
494 + }
495 + this.setChecked(true);
496 + checkedControllerAction = this;
497 + currentController = HeadControllers.INSTANCE.getController(id);
498 + }
499 + };
500 + if (checkedControllerAction == null) {
501 + action.run();
502 + }
503 + menuManager.add(action);
504 +}
505 +{{/code}}
506 +)))
507 +1. (((
508 +Implement the following method in the {{code language="none"}}TuringTape{{/code}} class:
509 +
510 +{{code language="java"}}
511 +public void execute(final IHeadController controller)
512 +{{/code}}
513 +
514 +The method shall have the following properties:
515 +
516 +\\
517 +
518 +* Determine the character at the current head position using
519 +
520 +{{code language="none"}}
521 +getCharacter(getHeadPosition())
522 +{{/code}}.
523 +* Call
524 +
525 +{{code language="none"}}
526 +controller.nextCommand()
527 +{{/code}} with the current character as parameter.
528 +* Depending on the action in the returned head command, either write the returned new character to the current position in text (
529 +
530 +{{code language="none"}}
531 +WRITE
532 +{{/code}}), or write the blank symbol (
533 +
534 +{{code language="none"}}
535 +ERASE
536 +{{/code}}), or do nothing. If the current position exceeds the end of the text, append enough blank characters up to the current position, then append the new character.
537 +* Depending on the direction in the returned head command, either move the head to the left (but no further than position 0), or to the right, or do nothing.
538 +)))
539 +1. Copy the files [[attach:step.gif]]and [[attach:reset.gif]]to the icons folder.
540 +1. Add an action to the toolbar of the Tape view with text {{code language="none"}}Step{{/code}} and icon {{code language="none"}}step.png{{/code}} which does the following:\\
541 +1*. Check whether the current head controller is not {{code language="none"}}null{{/code}}, than call {{code language="none"}}tape.execute(currentController){{/code}}.
542 +1*. Refresh the table viewer with its {{code language="none"}}refresh(){{/code}} method.
543 +1*. (((
544 +Note: actions don't need images, but only image descriptors. Thus, to set the action's icon to {{code language="none"}}step.png{{/code}}, you can use something like the following:
545 +
546 +{{code language="java"}}
547 +Activator.imageDescriptorFromPlugin(Activator.PLUGIN_ID, "path_to_icon");
548 +{{/code}}
549 +)))
550 +1. Add another action with text Reset and icon reset.png which does the following:\\
551 +1*. Check whether the current head controller is not {{code language="none"}}null{{/code}}, then call the {{code language="none"}}reset(){{/code}} method on {{code language="none"}}currentController{{/code}}.
552 +1*. Set the current head position to 1.
553 +1*. Refresh the table viewer with its {{code language="none"}}refresh(){{/code}} method.
554 +
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Confluence.Code.ConfluencePageClass[0]
Id
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1 -2982297
1 +2982314
URL
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1 -https://rtsys.informatik.uni-kiel.de/confluence//wiki/spaces/WS12EclPract/pages/2982297/The Plug-in Architecture of Eclipse
1 +https://rtsys.informatik.uni-kiel.de/confluence//wiki/spaces/WS12EclPract/pages/2982314/The Plug-in Architecture of Eclipse

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