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Creating a GEF Editor – Part 5: Loading the Model from an EMF File

Last updated on 2014-09-05

Previous Tutorial: Creating a GEF Editor – Part 4: Showing the Model on the Editor

Hi everyone. In this tutorial we will learn how to load the model from an EMF file (Seemed easy but took me some searching to find how this is done, and I’m not sure I’m doing it the best way it could be done), and in the way we’ll also be expanding our model definition to match our requirements. If you didn’t generate your EMF editor code, please do so now, because we’ll be using it to bootstrap our EMF file before we open it using the GEF editor. So let’s get started.

  1. In the previous tutorial, we used a mock model hard-coded into our diagram, and we also gave the OPMObject figures random locations in our diagram. We’ll fix this in two steps, first by expanding the model’s definition and second by loading the model data from a file.
  2. Now we will add constraints information to the OPMThing model class. This requires three steps: first, we need to add the org.eclipse.draw2d plugin as a required dependency of the project to allow us to use the classes in this library in our model (an example how to add new dependencies is was shown in the 3rd tutorial). Second, we define a new EData Type, which is the way to connect Ecore models with existing data types outside the model. And third, the constraints attribute will be added to the OPMThing model class.
  3. Right-click on the package node of the opm.ecoremodel and select “New Child”->”EData Type”. This will add a new entry to the package node as shown below:

    As usual, the properties of this node are edited in the properties view of the eclipse framework, so if they are not already open double click on the new node to open the properties editor. The data type we are defining is a connection to the Rectangle that is defined in org.eclipse.draw2d.geometry package, so we’ll name our new data type “Rectangle” and will set the “Instance Type Name” property to org.eclipse.draw2d.geometry.Rectangle.
  4. Now add a new attribute to the OPMObject class called “constraints” and set its EType to Rectangle (if you forgot how to do this, go to the first tutorial for a short reminder). Your model should now look like this:
  5. Save the Ecore model and generate all code from the genmodel file. This is good but we are still missing one piece in the puzzle. Although the EMF framework know how to reference the Rectangle class, it does not know how to serialize this class to a String, which is one of the thing that EMF has to do. Therefore we must provide one implementation ourselves by editing the code generated by the EMF framework. You are probably saying “Hey, you’ll edit the EMF code and next time you generate the model code the core you wrote will be erased and you will have to write it again! This is a nightmare!!!”. But no. See, EMF code generation is very smart. The code generated by the EMF framework contains comment annotations (that is, annotations that are part of the comments of a class/method/type) that can be read by the framework before new code is generated. In general, all generated code is annotated with the @generated annotation, so if we want to change the generated code, we simply append “NOT” after the comment and in the next time code is generated, this function will not be overwritten by the code generator. Nice, ah? So lets get going. Open the package found in the project. There are two functions that must be re-written: createRectangleFromString and convertRectangleToString. I decided to represent a rectangle as a comma separated lists of values: “x,y,width,height”, as shown in the code below:
    	 * <!-- begin-user-doc -->
    	 * Create a <code>Rectangle</code> instance from a <code>String</code>. The expected
    	 * representation is "x,y,width,height". Illegal representations will return a null
    	 * value. 
    	 * <!-- end-user-doc -->
    	 * @generated NOT
    	public Rectangle createRectangleFromString(EDataType eDataType, String initialValue) {
    		if(initialValue == null) {
    			return null;
    		initialValue.replaceAll("\\s", "");
    		String[] values = initialValue.split(",");
    		if(values.length != 4) {
    			return null;
    		Rectangle rect = new Rectangle();
    		try {
    			rect.setLocation(Integer.parseInt(values[0]), Integer.parseInt(values[1]));
    			rect.setSize(Integer.parseInt(values[2]), Integer.parseInt(values[3]));
    		} catch(NumberFormatException e) {
    			rect = null;
    		return rect;
    	 * <!-- begin-user-doc -->
    	 * Convert a <code>Rectangle</code> to a <code>String</code> representation. The
    	 * <code>Rectangle</code> is represented as "x,y,width,heigth". 
    	 * <!-- end-user-doc -->
    	 * @generated NOT 
    	public String convertRectangleToString(EDataType eDataType, Object instanceValue) {
    		if(instanceValue == null) {
    			return null;
    		Rectangle rect = (Rectangle) instanceValue;
    		return rect.x+","+rect.y+","+rect.width+","+rect.height;

    Please save all of your work. I you want, you can check that the code generation does work as expected by re-generating the code and checking that the OPMFactoryImpl class still contains the code marked by @generated NOT.

  6. We are done with the model, now we must load the model file into our diagram editor. For this, we’ll override the GraphicalEditor.init method, which is called shortly after the EditPart is instantiated, and is provided by the eclipse workbench with an instance of an IEditorInput class from where we can fetch our model. But before we do this, we must add two more plug-in dependencies to our project: org.eclipse.ui.ide and org.eclipse.core.resources. So add the dependencies and override the GraphicalEditor.init with the following code:
    	@Override public void init(IEditorSite site, IEditorInput input) throws PartInitException {
    		super.init(site, input);
    		OPMPackage.eINSTANCE.eClass(); // This initializes the OPMPackage singleton implementation.
    		ResourceSet resourceSet = new ResourceSetImpl();
    		if(input instanceof IFileEditorInput) {
    			IFileEditorInput fileInput = (IFileEditorInput) input;
    			IFile file = fileInput.getFile();
    			opdResource = resourceSet.createResource(URI.createURI(file.getLocationURI().toString()));
    			try {
    				opd = (ObjectProcessDiagram) opdResource.getContents().get(0);
    			} catch(IOException e) {
    				// TODO do something smarter.
    				opdResource = null;

    We have also added two class fields to hold the model and the resource from where the model was loaded:

    	private Resource opdResource;
    	private ObjectProcessDiagram opd;

    Changed the source of contents of the diagram (in the initializeGraphicalViewer method):

    	@Override protected void initializeGraphicalViewer() {

    and of course, added lots of imports:

    import org.eclipse.core.resources.IFile;
    import org.eclipse.core.runtime.IProgressMonitor;
    import org.eclipse.emf.common.util.URI;
    import org.eclipse.emf.ecore.resource.Resource;
    import org.eclipse.emf.ecore.resource.ResourceSet;
    import org.eclipse.emf.ecore.resource.impl.ResourceSetImpl;
    import org.eclipse.gef.DefaultEditDomain;
    import org.eclipse.gef.palette.PaletteRoot;
    import org.eclipse.ui.IEditorInput;
    import org.eclipse.ui.IEditorSite;
    import org.eclipse.ui.IFileEditorInput;
    import org.eclipse.ui.PartInitException;

    After all this, your code should now compile with no errors.

  7. Last thing we need to do is read the constraints information from our model into our figures. Open the OPMObjectEditPart and replace the refreshVisuals method with the following code:
    	@Override protected void refreshVisuals() {
    		OPMObjectFigure figure = (OPMObjectFigure)getFigure();
    		OPMObject model = (OPMObject)getModel();
    		ObjectProcessDiagramEditPart parent = (ObjectProcessDiagramEditPart) getParent();
    		Rectangle layout = new Rectangle(model.getConstraints().x, model.getConstraints().y, 
    				model.getConstraints().width, model.getConstraints().height);
    		parent.setLayoutConstraint(this, figure, layout);
  8. Good. But before we can see our OPMObjects in our diagram, we must define them constraints. We’ll be doing this in the “OPM Model Editor” that is automatically generated by the EMF framework. So please execute the project, right-click on the model source file (in my case “TheBestOPMModel.opm”), and select “Open With”->”OPM Model Editor” (ignore problems that may occur while initializing the “OPM GEF Editor” and close it if it is open. They are probably caused by a malformed input file that does not contain yet the constraints field):

    This model editor looks very similar to the Ecore editor, and this is because they are both based on the same framework, so you should already know how to work with it. Navigate to the “Object Process Diagram” node on the editor, right-click and select “New Child”->”Object”:

    Now fill up the Object’s properties (in the properties view). I set them as follows:

    • Name: O1
    • Constraints: 50,50,50,50

  9. This is it. Right-click on your model file and select “Open With”->”OPM GEF Editor”. You should now see your object in the location you placed it.

    You can add more objects using the EMF editor and see the result (note that the diagram does not refresh automatically so you must close it and open it again to see the changes in the model. Refreshing the editor is something that will be handled in a future tutorial

The final eclipse project files can be downloaded here.

That’s all for today. If you have any problems, don’t hesitate to leave a comment. And thank you for your visit.

Next Tutorial: Creating a GEF Editor – Part 6: Model Refactoring and Editing Diagram Entities

Published inProgramming


  1. Fenglin Han Fenglin Han

    Dear author,
    your articles are really helpful. i am now facing a problem for extending an existing editor. i want the extension to be created in an eclipse fragment. what the minimum change should be done in the editor project? is it possible to just modify the models ecore file and create the view and editpart of the element in another fragment?

    yours sincerely,


    • admin admin

      Hi Simon. I am not sure I understand what you mean by “eclipse fragment”. Could you please give me a longer explanation?


      • Fenglin Han Fenglin Han

        the fragment is another type of plugin. its configure file is fragment.xml. not plugin.xml. it a logical extension of its extended plugin. If you see the TIGER (model transformation) project source code. you can discover some example. But after a few days of studying. it seems not applicable. But its not the question for me now.

  2. Lucian Lucian

    Dude, nice thing you got here, but if you don’t explain what the code does, is not a tutorial just a DIY example

    • admin admin

      I Lucian. From my experience the best way to learn is by reading code that works and does something similar to what you want to do, and then trying to learn why the code works. Since I am also learning GEF at this time, this is what I am doing. I plan on writing some more explanations on the internals of GEF but they are fairly complicated and not until I have full understanding of them I will be able to do this.
      But thanks anyway.

    • admin admin

      You can find it linked in my “useful links” page. Pretty useful but missing LOADS of examples. I’m trying to fill out that gap.

  3. Fenglin Han Fenglin Han

    i also think the mode persistence needs time studying. here is a piece of code for creating a model file.
    System.out.println(“create henshin file with name:”+name);
    IFile transformationFile = null;
    if (!project.getFile(name).equals(null))

            transformationFile = project.getFile(name); // such as file.exists()
                                                        // == false
        String contents = "";
        InputStream source = new ByteArrayInputStream(contents.getBytes());
        try {
            transformationFile.create(source, false, monitor);
        } catch (CoreException e) {

    i create a model transformation file with post-fix “.henshin”
    but the xmi file is encoded ascii, how to change it to utf-8?
    should i change some thing here? or should i change something during creating the resources?

    do you have any suggestions?

    yours sincerely


    • Fenglin Han Fenglin Han

      that’s not a problem either now. i have to set a encoding in the save options.
      Map options = new HashMap();

  4. Pham Quang Vinh Pham Quang Vinh

    Thanks you for your your tutorial, it is very interesting.
    I try this part 5 first time with the OPM model, the second time I try it with a real model. I arrive in the Step 7 :
    “Open With”->”OPM Model Editor”
    But I can not have the OPM Model Editor, I have just the GEF Editor, I dont know what is missing. Can you tell me what the “Model Editor” depends on, what to to for having this Model Editor in the list choice editor ?

    Thanks for your help !!

    • admin admin

      What do you mean “with a real model”? The editor only works with OPM models. This is defined in the plug-in’s description, when it tells that only files ending with “.opm” are opened by the editor.

      • Pham Quang Vinh Pham Quang Vinh

        In fact I’ve need to try for my company needs on a real models prototype of the company. I have some problems but it is ok know, thanks for your answer.

  5. Prasad Prasad

    Hey ADMIN,

    I just want to say that I really appreciate these tutorials. Specially that you have attached the working code for each tutorial.

    Thank you for sharing your knowledge.

  6. This tutorial series in general does an excellent job of walking through the mechanics of GEF, but it does not follow some of the best practices for MVC, in particular separating model data from view data. In this specific installment of the tutorial, view-specific information (e.g. the rectangle data) is being put into the model. This makes it impossible, for example, to have multiple views of the same model element, as each would have different rectangle information.

    • Hi, and thanks for the comment.
      What you say regarding the view/model is more complicated. In my case, part of my model is the location of the figure. Furthermore, the really correct implementation would need two models, one for the view and one for the data. But this is too much work, and frankly not worth the effort.

  7. José José


    I’m suffer a problem that I don’t recognize if it’s an IDE bug or it’s my mistake. My eclipse Luna (4.40RC3) can’t find the IFileEditorInput. However, if I press the shortcout CTRL + SHIFT + T eclipse can open it. WTF? I’ve added correctly the new dependency to the manifest plus other possible dependencies (org.eclipse.ui, org.eclipse.ui.ide, etc.). And I’ve also tried to add directly the .jar as a project-dependency (in the build path) and always appears the mark of “cannot resolve”.

    I’ve googled also but I can’t find a solution that would be OK for me. Could you give me some idea about the problem? How could I resolve it?


    • Hi Jose. This sometimes happened to me also, where dependencies that I know exist suddenly aren’t loaded. Sometimes restarting eclipse works. I you are using Maven, sometimes the problem is in the definitions there. Nothing of much help that I can say here.

  8. Rahul Kumar Upadhyay Rahul Kumar Upadhyay

    Hi ,

    I have downloaded your project of part 5 and in the new workspace while opening opm file with OPM model editor i am getting following exception :
    “org.eclipse.emf.ecore.resource.impl.ResourceSetImpl$1DiagnosticWrappedException: org.xml.sax.SAXParseExceptionpublicId: platform:/resource/ssssss/eeeeee.opm; systemId: platform:/resource/ssssss/eeeeee.opm; lineNumber: 1; columnNumber: 1; Premature end of file.”

    While debugging i have found that in OPMGraphicalEditor this issue is coming at following lines
    opd =(ObjectProcessDiagram)opdResource.getContents().get(0);

    Rahul Kumar Upadhyay

    • There is a problem parsing the model file you are using. This can be caused by changes I do all the time to the model. That’s the best I can help.

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