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This tutorial will teach you the basics of writing plugins that run inside the Eclipse framework. You will learn about editors, views, and extension points by creating one of each yourself.
There's a few things to do before we dive into the tutorial itself. For example, to do Eclipse programming, you will have to get your hands on an Eclipse installation first. Read through the following sections to get ready for the tutorial tasks.
For this tutorial, we need you to have Eclipse and Git installed:
Over the course of this tutorial, you will be writing a bit of code. Here's a few rules we ask you to follow:
de.cau.cs.rtprak.login
, where login
is your login name as used for your email address at the institute. From now on, this rule will apply to all tutorials. Once we start with the actual practical projects, we will choose another package name.During the tutorial, we will cover each topic only briefly, so it is always a good idea to find more information online. Here's some more resources that will prove helpful:
You will find that despite of all of these resources Eclipse is still not as well commented and documented as we'd like it to be. Finding out how stuff works in the world of Eclipse can thus sometimes be a challenge. However, this does not only apply to you, but also to many people who are conveniently connected by something called The Internet. It should go without saying that if all else fails, Google often turns up great tutorials or solutions to problems you may run into. And if it doesn't, Miro and I will be happy to help you as well.
We have created a Git repository for everyone to do his tutorials in. You can access the repository online through our Stash tool over here. You will first have to configure your Stash account:
You should now be able to access the repository. Clone it:
ssh://git@git.rtsys.informatik.uni-kiel.de:7999/PRAK/12ws-eclipse-tutorials.git .
(including the final dot, which tells git to clone the repository into the current directory instead of a subdirectory).You will use this repository for all your tutorial work, along with everyone else. To make sure that you don't interfere with each other, everyone will work on a different branch. This is not exactly how people usually use Git, but goes to demonstrate Git's flexibility... Add a branch for you to work in:
git checkout -b login_name
You have just added and checked out a new branch. Everything you commit will go to this branch. To push your local commits to the server (which you will need to do so we can access your results), do the following:
git push origin login_name
You would usually have to enter git pull
first, but since nobody will mess with your branch this won't be necessary. By the way, you only need to mention origin login_name
with the first git push
, since Git doesn't know where to push the branch yet. After the first time, Git remembers the information and it will be enough to just enter git push
.
OK, with all the preliminaries out of the way let's get working. Fire up Eclipse, choose an empty workspace, close the Welcome panel it will present you with and follow the following steps.
For our text editor to integrate into Eclipse, we need to create a plug-in project for it:
de.cau.cs.rtprak.login.simple
. Uncheck Use default location (which would put the project into your workspace), and put it into your local clone of the Git repository instead (the Location should read something like /path/to/git/repository/de.cau.cs.rtprak.login.simple
). Click Next.Simple (login)
. Also, make sure that Generate an activator and This plug-in will make contributions to the UI are both checked. Click Finish. (Eclipse might ask you whether you want to switch to the Plug-in Development Perspective, which configures Eclipse to provide the views that are important for plug-in development. Choose Yes. Or No. It won't have a big influence on your future...)plugin.xml
and META-INF/MANIFEST.MF
. (By the way, this would be a great time to research the editor and the two files online.) Basically, those two files provide information that tell Eclipse what other plug-ins your plug-in needs and how it works together with other plug-ins by providing extensions and extension points. Our new plug-in will depend on two other plug-ins, so switch to the Dependencies tab of the editor and add dependencies to org.eclipse.ui.editors
and org.eclipse.jface.text
. Save the editor and close it. (You can always reopen it by opening one of the two mentioned files from the Package Explorer.)We will now create the class that implements the simple text editor. There won't be any programming involved here since we're lazy; instead, we will just inherit from an existing simple text editor.
de.cau.cs.rtprak.login.simple.editors
. Name: SimpleEditorPart
. Superclass: org.eclipse.ui.editors.text.TextEditor
. Click Finish.For the editor to be available inside Eclipse, we will have to register it by adding an extension to an extension point.
org.eclipse.ui.editors
extension point and click Finish.de.cau.cs.rtprak.login.simple.editor
, the name to Simple Text Editor
, the icon to icons/turing-file.gif
, the extensions to simple
, the class to de.cau.cs.rtprak.login.simple.editors.SimpleEditorPart
, and the default to true
.It's time to test your new simple editor in a new Eclipse instance.
test
as the project name.test.simple
. This will create a new file with that name and open the file in your newly added text editor. (You can see that it is your editor by looking at the editor icon, which should look like the icon you downloaded and put into the icons folder.)The next task consists of creating a view that is able to display the state of a Turing Machine. We will do this using a table with one column, where each row represents an entry on the tape of the Turing Machine. The tape shall be infinite to one side, and the position of the read/write head shall be movable by two buttons. The content of the tape shall be determined by the currently active instance of our simple text editor.
In the following, we will be making use of the Standard Widget Toolkit (SWT) and JFace to build a user interface. It might be a good idea now to search for an introduction to SWT and JFace concepts on the Internet before you proceed. |
We will start by creating a class that will define the view.
TapeViewPart
in a new package de.cau.cs.rtprak.login.simple.views
that extends the ViewPart class. (make sure that in the New Java Class wizard, the option Inherited abstract methods is checked.)tableViewer
of type TableViewer.Your TableViewPart
contains a still empty method createPartControl
. This method will be responsible for creating the user interface components of your view. Add the following code to create the table we want to display:
Table table = new Table(parent, SWT.BORDER); table.setHeaderVisible(true); TableColumn column = new TableColumn(table, SWT.NONE); column.setWidth(80); column.setText("Tape Data"); tableViewer = new TableViewer(table); |
The setFocus
method controls what happens when your part gets the focus. Make sure the focus will then automatically be set to the table by adding the following code:
tableViewer.getControl().setFocus(); |
We will now have to register our new view with Eclipse so that it can be seamlessly integrated into the workbench.
icons
subfolder of your plug-in as you did it before. (You might need to refresh your project again if you did the copying outside of Eclipse.)plugin.xml
file in the Plugin Manifest Editor and switch to the Extensions tab.org.eclipse.ui.views
. Right-click the newly added extension and add a new view
element through the New menu.de.cau.cs.rtprak.login.simple.view
, name Tape
, class de.cau.cs.rtprak.login.simple.views.TapeViewPart
, category org.eclipse.ui
, icon icons/tape_head.gif
.When you start the application, you should now be able to open your view by clicking Window -> Show View -> Other.
The idea of JFace viewers is to abstract a bit from the underlying widget (in our case, the table) and instead work on data models that are to be viewed. Instead of adding items to the table directly, the table viewer is supplied with an input object, a content provider, and a label provider. The content provider allows the viewer to make sense of the input object and basically allows the viewer to access the input object's data. The label provider translates each item of data into text and icons that can be used to present the item to the user in the table.
We will now create content and label providers to do just that.
Create a class TuringTape
in a new package de.cau.cs.rtprak.login.simple.model
with the following fields:
private int headPosition = 1; private StringBuffer text = new StringBuffer(); |
Also add corresponding getter and setter methods. (You can simply right-click somewhere in the class and choose Source -> Generate Getters and Setters.)
Add two constants to the class:
public static final char START_CHAR = '\u25b7'; public static final char BLANK_CHAR = '\u25fb'; |
getCharacter(int pos)
that calculates the tape character at position pos
as follows:pos == 0
, return the character START_CHAR
.pos > text.length()
, return the character BLANK_CHAR
.pos - 1
.TuringTape
to TapeViewPart
and initialize it with a new instance.TapeData
in de.cau.cs.rtprak.login.simple.model
with two fields int index
and char character
, and add a constructor for initialization as well as corresponding getter methods.TapeContentProvider
in the de.cau.cs.rtprak.login.simple.views
package that implements IStructuredContentProvider.dispose()
and inputChanged()
may remain empty.getElements()
must return an array of objects, where each object must contain all necessary data to be displayed in a single row of the table. The number of returned objects corresponds to the number of rows.TuringTape
. The result of getElements()
shall be an array of TapeData
elements. The size of the array shall be one more than the maximum of the tape head position and the length of the tape text. The index and character of each tape data element shall be filled with i
and the result of turingTape.getCharacter(i)
, respectively, where i
is the array index of the element.TapeLabelProvider
in the de.cau.cs.rtprak.login.simple.views
package that extends BaseLabelProvider and implements ITableLabelProvider.tape
of type TuringTape
that is initialized from the constructor.presentImage
and absentImage
of type Image.Initialize each image using the following code, where path_to_image
is icons/head_present.gif
and icons/head_absent.gif
, respectively:
image = Activator.imageDescriptorFromPlugin(Activator.PLUGIN_ID, "path_to_image").createImage(); |
dispose()
in TapeLabelProvider
to dispose both images after calling super.dispose()
. (Right-click in the source-code and click Source -> Override/Implement Methods.)getColumnImage()
and getColumnText()
, first check whether the element is an instance of TapeData
and the column index is 0, and return null
otherwise. If the check passes, return the following:getColumnImage()
: presentImage
if the index given by the tape data element equals the current value of tape.getHeadPosition()
, absentImage
otherwise.getColumnText()
: a String
containing the character of the tape data element.Add the following lines to createPartControl()
in TapeViewPart
:
tableViewer.setContentProvider(new TapeContentProvider()); tableViewer.setLabelProvider(new TapeLabelProvider(tape)); tableViewer.setInput(tape); |
We will now add code to make the Tape view display the content of a currently active Simple Text Editor.
Add the following methods to SimpleEditorPart
:
/** * Returns the text that is currently displayed in the editor. * @return the currently displayed text */ public String getText() { return getDocumentProvider().getDocument(getEditorInput()).get(); } /** The listener that is currently registered for this editor. */ private IDocumentListener registeredListener; /** * Registers the given runnable as listener for changes to the text * of this editor. * @param runnable a runnable to register as text listener */ public void registerTextListener(final Runnable runnable) { registeredListener = new IDocumentListener() { public void documentAboutToBeChanged(DocumentEvent event) {} public void documentChanged(DocumentEvent event) { runnable.run(); } }; getDocumentProvider().getDocument(getEditorInput()) .addDocumentListener(registeredListener); } /** * Removes the last registered text listener. */ public void disposeTextListener() { if (registeredListener != null) { if (getDocumentProvider() != null) { getDocumentProvider().getDocument(getEditorInput()) .removeDocumentListener(registeredListener); } registeredListener = null; } } |
Add the following code to TapeViewPart
:
/** The editor part that is currently set as input for the viewer. */ private SimpleEditorPart currentInput; /** * Sets the displayed text of the given editor part as input of the * viewer, if the editor part is a SimpleEditorPart. * @param part workbench part to set as input */ private void setInput(final IWorkbenchPart part) { if (part instanceof SimpleEditorPart && part != currentInput) { if (currentInput != null) { currentInput.disposeTextListener(); } currentInput = (SimpleEditorPart) part; Runnable runnable = new Runnable() { public void run() { tape.setText(new StringBuffer(currentInput.getText())); tableViewer.refresh(); } }; runnable.run(); currentInput.registerTextListener(runnable); } } |
Add the following code to createPartControl()
:
IWorkbenchWindow workbenchWindow = getSite().getWorkbenchWindow(); IWorkbenchPage activePage = workbenchWindow.getActivePage(); if (activePage != null) { setInput(activePage.getActivePart()); } workbenchWindow.getPartService().addPartListener(new IPartListener() { public void partActivated(final IWorkbenchPart part) { setInput(part); } public void partDeactivated(final IWorkbenchPart part) {} public void partBroughtToTop(final IWorkbenchPart part) {} public void partClosed(final IWorkbenchPart part) {} public void partOpened(final IWorkbenchPart part) {} }); |
If we want to add buttons to the view's tool bar, we will have to ask its IToolbarManager to do that for us:
Get the tool bar manager using the following code:
IToolBarManager toolBarManager = getViewSite().getActionBars().getToolBarManager(); |
run()
method.tableViewer.refresh()
after any change to the tape.headPosition
variable.If you open an instance of the simple text editor and open the Tape view, the view should correctly display the editor's text on a tape, and the L and R buttons should move the tape head.
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 plugin.xml
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).
We will start by defining a class representing a command that will be passed to a selected head controller.
HeadCommand
to the package de.cau.cs.rtprak.login.simple.controller
.Action
with values WRITE
, ERASE
, and NULL
.Direction
with values LEFT
, RIGHT
, and NONE
.Add the following private fields:
private Action action; private Direction direction; private char newChar; |
We will now define an interface that all head controllers will have to implement:
IHeadController
in the package de.cau.cs.rtprak.login.simple.controller
.Add the following methods to the interface:
/** * Calculate the next command depending on the currently seen character. * @param character the currently seen character * @return the next command specifying which character to write and * which direction to move the head */ HeadCommand nextCommand(char character); /** * Reset the internal state of the head controller. */ void reset(); |
We will now define the extension point that head controllers will be registered at.
plugin.xml
file in the Plugin Manifest Editor and switch to the Extension Points tab.de.cau.cs.rtprak.login.simple.headControllers
as the extension point's ID, and Head Controllers
as its name. Shorten the schema file's file name to schema/headControllers.exsd
. Make sure that Edit extension point schema when done is checked and click Finish.controller
.controller
element:id
, use required
, type string
, translatable false
.name
, use required
, type string
, translatable true
.class
, use required
, type java
, implements de.cau.cs.rtprak.login.simple.controller.IHeadController
. 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.extension
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.de.cau.cs.rtprak.login.simple.controller
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 IHeadController
. For this to work, those plug-ins must have access to that interface; thus, we have to export the package containing it.We will now add a class that will be in charge of loading all extensions registered at our new extension point.
Add a class HeadControllers
to the package de.cau.cs.rtprak.login.simple.controller
. Add the following code, replacing login
with your login name in EXTENSION_POINT_ID
as usual:
/** * Class that gathers extension data from the 'headControllers' extension point * and publishes this data using the singleton pattern. * @author msp */ public class HeadControllers { /** Identifier of the extension point */ public final static String EXTENSION_POINT_ID = "de.cau.cs.rtprak.login.simple.headControllers"; /** The singleton instance of the {@code HeadControllers} class */ public final static HeadControllers INSTANCE = new HeadControllers(); /** list of head controller ids with associated names. */ private List<String[]> controllerNames = new LinkedList<String[]>(); /** map of controller ids to their runtime instances. */ private Map<String, IHeadController> controllerMap = new HashMap<String, IHeadController>(); /** * Creates an instance of this class and gathers extension data. */ HeadControllers() { IConfigurationElement[] elements = Platform.getExtensionRegistry() .getConfigurationElementsFor(EXTENSION_POINT_ID); for (IConfigurationElement element : elements) { if ("controller".equals(element.getName())) { String id = element.getAttribute("id"); String name = element.getAttribute("name"); if (id != null && name != null) { try { IHeadController controller = (IHeadController)element .createExecutableExtension("class"); controllerNames.add(new String[] {id, name}); controllerMap.put(id, controller); } catch (CoreException exception) { StatusManager.getManager().handle(exception, Activator.PLUGIN_ID); } } } } } /** * Returns a list of controller ids and names. The arrays in the list are * all of size 2: the first element is an id, and the second element is the * associated name. The controller name is a user-friendly string to be * displayed in the UI. * @return a list of controller ids and names */ public List<String[]> getControllerNames() { return controllerNames; } /** * Returns the head controller instance for the given id. * @param id identifier of a head controller * @return the associated controller */ public IHeadController getController(final String id) { return controllerMap.get(id); } } |
We will now have to add support for head controllers to our view.
TapeViewPart
class and add the private fields checkedControllerAction
of type IAction and currentController
of type IHeadController
.Add a list of registered head controllers to the view's menu (which can be opened using the small white triangle) in the createPartControl()
method:
IMenuManager menuManager = getViewSite().getActionBars().getMenuManager(); for (String[] controllerName : HeadControllers.INSTANCE.getControllerNames()) { final String id = controllerName[0]; String name = controllerName[1]; Action action = new Action(name, IAction.AS_RADIO_BUTTON) { public void run() { if (checkedControllerAction != null) { checkedControllerAction.setChecked(false); } this.setChecked(true); checkedControllerAction = this; currentController = HeadControllers.INSTANCE.getController(id); } }; if (checkedControllerAction == null) { action.run(); } menuManager.add(action); } |
Implement the following method in the TuringTape
class:
public void execute(final IHeadController controller) |
The method shall have the following properties:
getCharacter(getHeadPosition())
.controller.nextCommand()
with the current character as parameter.WRITE
), or write the blank symbol (ERASE
), 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.Step
and icon step.png
which does the following:null
, than call tape.execute(currentController)
.refresh()
method.Note: actions don't need images, but only image descriptors. Thus, to set the action's icon to step.png
, you can use something like the following:
Activator.imageDescriptorFromPlugin(Activator.PLUGIN_ID, "path_to_icon"); |
null
, then call the reset()
method on currentController
.refresh()
method.Before creating a proper head controller in another plug-in, we will add a test controller to check whether all this stuff works.
Add a new class NullController
to the de.cau.cs.rtprak.login.simple.controllers
package:
/** * Head controller that does nothing, for testing. * @author msp */ public class NullController implements IHeadController { /** * {@inheritDoc} */ public HeadCommand nextCommand(final char character) { return new HeadCommand(Action.NULL, Direction.NONE, '_'); } /** * {@inheritDoc} */ public void reset() { } } |
de.cau.cs.rtprak.login.simple.headControllers
extension point. Add a controller
element with ID de.cau.cs.rtprak.login.simple.nullController
, name Null Controller
, and class de.cau.cs.rtprak.login.simple.controller.NullController
.NullController
class. You can actually change both while the application is running, but only if you have started it in the Debug mode. In that case, Eclipse will actually hot-swap your changes into the running application. Sorcery!We will now create a new plug-in with a new head controller:
de.cau.cs.rtprak.login.simple.extension
. In the Plugin Manifest Editor, add de.cau.cs.rtprak.login.simple
to the dependencies of the new plug-in.IHeadController
:hello
, the controller shall generate hellohellohellohe...
.Congratulations, you just made a big step towards understanding how Eclipse works. Plus, you've refreshed your knowledge on Turing Machines along the way. Eclipse is an industry standard technology, and having experience programming against it is a valuable skill for you.
If you have any comments and suggestions for improvement concerning this tutorial, please don't hesitate to tell us about them!