[518524] Adds command API to update pages dynamically

A new API allows custom page providers to tell aird editors owning their
pages to either refresh the page's tab, to remove it or to reorder it to
a new location when a resource set event of the session behind the
editor occurs.

Bug: 518524
Change-Id: Id681ac5c3ede24faffa80896ce6376f24e03bf5e
Signed-off-by: pguilet <pierre.guilet@obeo.fr>

14 files changed, 596 insertions, 49 deletions

diff --git a/plugins/org.eclipse.sirius.ui.debug/src/org/eclipse/sirius/ui/debug/pages/DebugPage.java b/plugins/org.eclipse.sirius.ui.debug/src/org/eclipse/sirius/ui/debug/pages/DebugPage.java
index d30b575623..4bbf77462e 100644
--- a/plugins/org.eclipse.sirius.ui.debug/src/org/eclipse/sirius/ui/debug/pages/DebugPage.java
+++ b/plugins/org.eclipse.sirius.ui.debug/src/org/eclipse/sirius/ui/debug/pages/DebugPage.java
@@ -10,12 +10,14 @@
  *******************************************************************************/
 package org.eclipse.sirius.ui.debug.pages;
 
+import org.eclipse.emf.transaction.ResourceSetChangeEvent;
 import org.eclipse.jface.layout.GridLayoutFactory;
 import org.eclipse.sirius.business.api.session.Session;
 import org.eclipse.sirius.ui.editor.SessionEditor;
 import org.eclipse.sirius.ui.editor.api.pages.AbstractSessionEditorPage;
 import org.eclipse.sirius.ui.editor.api.pages.DefaultSessionEditorPage;
 import org.eclipse.sirius.ui.editor.api.pages.PageProviderRegistry.PositioningKind;
+import org.eclipse.sirius.ui.editor.api.pages.PageUpdateCommandBuilder.PageUpdateCommand;
 import org.eclipse.swt.SWT;
 import org.eclipse.swt.layout.GridData;
 import org.eclipse.swt.widgets.Composite;
@@ -43,16 +45,6 @@ public class DebugPage extends AbstractSessionEditorPage {
         this.session = editor.getSession();
     }
 
-    /*
-     * (non-Javadoc)
-     * @see org.eclipse.ui.forms.editor.FormPage#dispose()
-     */
-    @Override
-    public void dispose() {
-        // TODO Auto-generated method stub
-        super.dispose();
-    }
-
     @Override
     protected void createFormContent(IManagedForm managedForm) {
         super.createFormContent(managedForm);
@@ -81,4 +73,9 @@ public class DebugPage extends AbstractSessionEditorPage {
         return PositioningKind.AFTER;
     }
 
+    @Override
+    public PageUpdateCommand notifyAndGetUpdateCommands(ResourceSetChangeEvent resourceSetChangeEvent) {
+        return null;
+    }
+
 }
diff --git a/plugins/org.eclipse.sirius.ui.debug/src/org/eclipse/sirius/ui/debug/pages/DebugPageProvider.java b/plugins/org.eclipse.sirius.ui.debug/src/org/eclipse/sirius/ui/debug/pages/DebugPageProvider.java
index 9b5e0feb64..d0575a665f 100644
--- a/plugins/org.eclipse.sirius.ui.debug/src/org/eclipse/sirius/ui/debug/pages/DebugPageProvider.java
+++ b/plugins/org.eclipse.sirius.ui.debug/src/org/eclipse/sirius/ui/debug/pages/DebugPageProvider.java
@@ -17,7 +17,6 @@ import java.util.function.Supplier;
 
 import org.eclipse.sirius.ui.editor.SessionEditor;
 import org.eclipse.sirius.ui.editor.api.pages.AbstractSessionEditorPage;
-import org.eclipse.sirius.ui.editor.api.pages.DefaultSessionEditorPage;
 import org.eclipse.sirius.ui.editor.api.pages.PageProvider;
 
 /**
@@ -33,7 +32,7 @@ public class DebugPageProvider extends PageProvider {
     @Override
     public Map<String, Supplier<AbstractSessionEditorPage>> getPages(SessionEditor editor) {
         Map<String, Supplier<AbstractSessionEditorPage>> resultMap = new HashMap<>();
-        resultMap.put(DefaultSessionEditorPage.PAGE_ID, () -> {
+        resultMap.put(DebugPage.PAGE_ID, () -> {
             return new DebugPage(editor, DebugPage.PAGE_ID, DEBUG_PAGE_TITLE);
         });
         return resultMap;
diff --git a/plugins/org.eclipse.sirius.ui.editor/plugin.properties b/plugins/org.eclipse.sirius.ui.editor/plugin.properties
index 9bb46ce4e2..456fadea1c 100644
--- a/plugins/org.eclipse.sirius.ui.editor/plugin.properties
+++ b/plugins/org.eclipse.sirius.ui.editor/plugin.properties
@@ -38,4 +38,5 @@ GraphicalSemanticModelsHandler_addModelButton_tooltip=Add model
 DefaultSessionEditorPage_closeSession_action_label=Unload models
 DefaultSessionEditorPage_closeSession_action_tooltip=Unload models and close all associated editors
 DefaultSessionEditorPage_selectFilterAction_tooltip=Customize view...
-DefaultSessionEditorPage_collapseAllAction_tooltip=Collapse all
\ No newline at end of file
+DefaultSessionEditorPage_collapseAllAction_tooltip=Collapse all
+SessionEditor_PageCommand_Integrity_Error=Some page update commands from page {0} were ignored because a remove command was executed first and thus no update can be done anymore. 
diff --git a/plugins/org.eclipse.sirius.ui.editor/src/org/eclipse/sirius/ui/editor/Messages.java b/plugins/org.eclipse.sirius.ui.editor/src/org/eclipse/sirius/ui/editor/Messages.java
index 1669295f31..974866d73c 100644
--- a/plugins/org.eclipse.sirius.ui.editor/src/org/eclipse/sirius/ui/editor/Messages.java
+++ b/plugins/org.eclipse.sirius.ui.editor/src/org/eclipse/sirius/ui/editor/Messages.java
@@ -97,6 +97,9 @@ public final class Messages {
     @TranslatableMessage
     public static String GraphicalSemanticModelsHandler_addModelButton_tooltip;
 
+    @TranslatableMessage
+    public static String SessionEditor_PageCommand_Integrity_Error;
+
     // CHECKSTYLE:ON
 
     private Messages() {
diff --git a/plugins/org.eclipse.sirius.ui.editor/src/org/eclipse/sirius/ui/editor/SessionEditor.java b/plugins/org.eclipse.sirius.ui.editor/src/org/eclipse/sirius/ui/editor/SessionEditor.java
index b54fc2e5e3..8f507c360d 100644
--- a/plugins/org.eclipse.sirius.ui.editor/src/org/eclipse/sirius/ui/editor/SessionEditor.java
+++ b/plugins/org.eclipse.sirius.ui.editor/src/org/eclipse/sirius/ui/editor/SessionEditor.java
@@ -14,6 +14,7 @@ import java.lang.reflect.InvocationTargetException;
 import java.text.MessageFormat;
 import java.util.EventObject;
 import java.util.List;
+import java.util.Vector;
 import java.util.stream.Collectors;
 
 import org.eclipse.core.resources.IFile;
@@ -28,6 +29,8 @@ import org.eclipse.emf.common.command.CommandStackListener;
 import org.eclipse.emf.common.ui.URIEditorInput;
 import org.eclipse.emf.common.util.URI;
 import org.eclipse.emf.edit.domain.EditingDomain;
+import org.eclipse.emf.transaction.ResourceSetChangeEvent;
+import org.eclipse.emf.transaction.ResourceSetListenerImpl;
 import org.eclipse.jface.dialogs.ErrorDialog;
 import org.eclipse.sirius.business.api.modelingproject.ModelingProject;
 import org.eclipse.sirius.business.api.session.Session;
@@ -38,12 +41,18 @@ import org.eclipse.sirius.ui.business.api.session.IEditingSession;
 import org.eclipse.sirius.ui.business.api.session.SessionUIManager;
 import org.eclipse.sirius.ui.editor.api.pages.AbstractSessionEditorPage;
 import org.eclipse.sirius.ui.editor.api.pages.PageProviderRegistry;
+import org.eclipse.sirius.ui.editor.api.pages.PageUpdateCommandBuilder.PageUpdateCommand;
 import org.eclipse.sirius.ui.editor.internal.pages.PageProviderListener;
+import org.eclipse.sirius.ui.editor.internal.pages.RemovePageCommand;
+import org.eclipse.sirius.ui.editor.internal.pages.RenameTabLabelCommand;
+import org.eclipse.sirius.ui.editor.internal.pages.ReorderPageCommand;
 import org.eclipse.sirius.ui.tools.api.views.modelexplorerview.IModelExplorerView;
 import org.eclipse.sirius.viewpoint.provider.SiriusEditPlugin;
 import org.eclipse.swt.SWT;
 import org.eclipse.swt.custom.CTabFolder;
 import org.eclipse.swt.custom.CTabItem;
+import org.eclipse.swt.widgets.Composite;
+import org.eclipse.swt.widgets.TabItem;
 import org.eclipse.ui.IEditorInput;
 import org.eclipse.ui.IEditorPart;
 import org.eclipse.ui.IEditorSite;
@@ -74,6 +83,33 @@ import org.eclipse.ui.views.properties.tabbed.TabbedPropertySheetPage;
  */
 public class SessionEditor extends SharedHeaderFormEditor implements ITabbedPropertySheetPageContributor, IModelExplorerView, SessionListener, ISiriusEditor, PageProviderListener {
     /**
+     * This listener listens to any change in the session's resource set and
+     * notifies all pages when such change happens.
+     * 
+     * @author <a href="mailto:pierre.guilet@obeo.fr">Pierre Guilet</a>
+     *
+     */
+    private final class SessionResourceSetListener extends ResourceSetListenerImpl {
+        @Override
+        public void resourceSetChanged(ResourceSetChangeEvent event) {
+            int pageCount = SessionEditor.this.getPageCount();
+            for (int i = 0; i < pageCount; i++) {
+                Object page = SessionEditor.this.pages.get(i);
+                if (page instanceof AbstractSessionEditorPage) {
+                    AbstractSessionEditorPage customPage = (AbstractSessionEditorPage) page;
+                    PageUpdateCommand updateCommand = customPage.notifyAndGetUpdateCommands(event);
+                    executeUpdateCommands(customPage, updateCommand);
+                }
+            }
+        }
+
+        @Override
+        public boolean isPostcommitOnly() {
+            return true;
+        }
+    }
+
+    /**
      * The editor's id.
      */
     public static final String EDITOR_ID = "org.eclipse.sirius.ui.editor.session"; //$NON-NLS-1$
@@ -101,6 +137,12 @@ public class SessionEditor extends SharedHeaderFormEditor implements ITabbedProp
      */
     private PageProviderRegistry pageRegistry;
 
+    /**
+     * This listener listens to any change in the session's resource set and
+     * notifies all pages when such change happens.
+     */
+    private SessionResourceSetListener resourceSetListener;
+
     @Override
     protected void addPages() {
         updatePages();
@@ -122,16 +164,7 @@ public class SessionEditor extends SharedHeaderFormEditor implements ITabbedProp
             int pageIndex = pages.indexOf(page);
             if (pageIndex != -1) {
                 if (pageIndex != i) {
-                    // page already exists so we reuse its control in a new
-                    // tab to avoid loosing states like expanded items.
-                    cTabF.getItem(pageIndex).dispose();
-                    pages.remove(pageIndex);
-                    page.setIndex(i);
-
-                    CTabItem item = new CTabItem(cTabF, SWT.NONE, i);
-                    item.setText(page.getTitle());
-                    item.setControl(page.getPartControl());
-                    pages.add(i, page);
+                    updatePageTabPosition(cTabF, page, pageIndex, i);
                 }
             } else {
                 try {
@@ -152,6 +185,61 @@ public class SessionEditor extends SharedHeaderFormEditor implements ITabbedProp
         }
 
         cTabF.getParent().layout();
+        setActivePage(activePage);
+    }
+
+    /**
+     * Update the page tab position at the given original index to the new
+     * target index.
+     * 
+     * @param cTabF
+     *            the {@link CTabFolder} containing the {@link TabItem}.
+     * @param page
+     *            the page associated to the tab item to update.
+     * @param originalPositionIndex
+     *            the position index of the tab item to update.
+     * @param targetPositionIndex
+     *            the target index the tab item should have. the
+     * 
+     * 
+     */
+    private void updatePageTabPosition(CTabFolder cTabF, AbstractSessionEditorPage page, int originalPositionIndex, int targetPositionIndex) {
+        // page already exists so we reuse its control in a new
+        // tab to avoid loosing states like expanded items.
+        cTabF.getItem(originalPositionIndex).dispose();
+        pages.remove(originalPositionIndex);
+
+        CTabItem item = new CTabItem(cTabF, SWT.NONE, targetPositionIndex);
+        item.setText(page.getTitle());
+        item.setControl(page.getPartControl());
+        pages.add(targetPositionIndex, page);
+
+        updatePageIndices(0);
+    }
+
+    /**
+     * Update page indices.
+     * 
+     * @param start
+     *            start index from which index updating is done.
+     */
+    private void updatePageIndices(int start) {
+        for (int i = start; i < pages.size(); i++) {
+            Object page = pages.get(i);
+            if (page instanceof IFormPage) {
+                IFormPage fpage = (IFormPage) page;
+                fpage.setIndex(i);
+            }
+        }
+    }
+
+    /**
+     * Set the given page as this editor active page if such page exists.
+     * 
+     * @param activePage
+     *            the page to set as the active page of this editor.
+     */
+    public void setActivePage(IFormPage activePage) {
         if (activePage != null) {
             int activePageIndex = pages.indexOf(activePage);
             if (activePageIndex != -1) {
@@ -183,11 +271,9 @@ public class SessionEditor extends SharedHeaderFormEditor implements ITabbedProp
             ErrorDialog.openError(getSite().getShell(), MessageFormat.format(Messages.UI_SessionEditor_session_loading_error_message, new Object[0]),
                     MessageFormat.format(Messages.UI_SessionEditor_inputNotHandled_error_message, editorInput.getClass().getSimpleName()), Status.CANCEL_STATUS);
         }
-
         try {
             if (sessionResourceURI != null) {
                 final URI sessionResourceURIFinal = sessionResourceURI;
-
                 IFile file = ResourcesPlugin.getWorkspace().getRoot().getFile(new Path(sessionResourceURIFinal.toPlatformString(true)));
                 IProject project = file.getProject();
                 if (ModelingProject.hasModelingProjectNature(project)) {
@@ -199,12 +285,10 @@ public class SessionEditor extends SharedHeaderFormEditor implements ITabbedProp
                     setPartName(sessionResourceURIFinal.lastSegment());
                     setContentDescription(sessionResourceURIFinal.toPlatformString(true));
                 }
-
                 // until we find a way to load session independently from the
                 // editor, session loading blocks the editor opening with a
                 // progress monitor.
                 PlatformUI.getWorkbench().getProgressService().busyCursorWhile((monitor) -> {
-
                     SubMonitor subMonitor = SubMonitor.convert(monitor, 1);
                     subMonitor.beginTask(MessageFormat.format(Messages.UI_SessionEditor_session_loading_task_title, new Object[0]), 1);
                     session = SessionManager.INSTANCE.getSession(sessionResourceURIFinal, subMonitor);
@@ -216,6 +300,9 @@ public class SessionEditor extends SharedHeaderFormEditor implements ITabbedProp
                     editingSession.open();
                     editingSession.attachEditor(this);
 
+                    resourceSetListener = new SessionResourceSetListener();
+                    session.getTransactionalEditingDomain().addResourceSetListener(resourceSetListener);
+
                     subMonitor.worked(1);
                     subMonitor.done();
                 });
@@ -254,6 +341,10 @@ public class SessionEditor extends SharedHeaderFormEditor implements ITabbedProp
             pageRegistry.removeRegistryListener(this);
             pageRegistry = null;
         }
+        if (resourceSetListener != null && session != null && session.getTransactionalEditingDomain() != null) {
+            session.getTransactionalEditingDomain().removeResourceSetListener(resourceSetListener);
+            resourceSetListener = null;
+        }
         if (session != null) {
             final IEditingSession editingSession = SessionUIManager.INSTANCE.getUISession(session);
             if (editingSession != null) {
@@ -374,4 +465,133 @@ public class SessionEditor extends SharedHeaderFormEditor implements ITabbedProp
     public Session getSession() {
         return session;
     }
+
+    /**
+     * Execute the given {@link PageUpdateCommand}. If a remove command is
+     * present, other update command will be ignored.
+     * 
+     * @param customPage
+     *            the page updated.
+     * @param updateCommand
+     *            the commands this editor must execute to update the page.
+     */
+    private void executeUpdateCommands(AbstractSessionEditorPage customPage, PageUpdateCommand updateCommand) {
+        if (updateCommand != null) {
+            boolean removeCommandExecuted = false;
+            if (updateCommand.getRemoveCommand() != null) {
+                executeRemoveCommand(updateCommand.getRemoveCommand(), SessionEditor.this, customPage);
+                removeCommandExecuted = true;
+            }
+            if (!removeCommandExecuted && updateCommand.getReorderCommand() != null) {
+                executeReorderCommand(updateCommand.getReorderCommand(), SessionEditor.this, customPage);
+            } else {
+                SessionEditorPlugin.getPlugin().error(MessageFormat.format(Messages.SessionEditor_PageCommand_Integrity_Error, customPage.getClass().getName()), null);
+            }
+            if (!removeCommandExecuted && updateCommand.getRenameCommand() != null) {
+                executeRenameCommand(updateCommand.getRenameCommand(), SessionEditor.this, customPage);
+            } else {
+                SessionEditorPlugin.getPlugin().error(MessageFormat.format(Messages.SessionEditor_PageCommand_Integrity_Error, customPage.getClass().getName()), null);
+            }
+        }
+    }
+
+    /**
+     * Execute the reorder command.
+     * 
+     * @param pageUpdateCommand
+     *            the command to execute containing execution information.
+     * @param editor
+     *            the editor calling for a page reordering.
+     * @param page
+     *            the page reordered.
+     */
+    private void executeReorderCommand(ReorderPageCommand pageUpdateCommand, SessionEditor editor, AbstractSessionEditorPage page) {
+        PlatformUI.getWorkbench().getDisplay().asyncExec(() -> {
+            Composite container = editor.getContainer();
+            if (container instanceof CTabFolder) {
+                CTabFolder tabFolder = (CTabFolder) editor.getContainer();
+                IFormPage activePage = editor.getActivePageInstance();
+
+                int targetPageIndex = -1;
+                String targetPageId = pageUpdateCommand.getTargetPageId();
+                for (Object object : pages) {
+                    if (object instanceof AbstractSessionEditorPage && targetPageId.equals(((AbstractSessionEditorPage) object).getId())) {
+                        targetPageIndex = ((AbstractSessionEditorPage) object).getIndex();
+                        break;
+                    }
+                }
+
+                int commandingPageIndex = pages.indexOf(page);
+                if (commandingPageIndex != -1 && targetPageIndex != -1) {
+                    switch (pageUpdateCommand.getPositioningKind()) {
+                    case AFTER:
+                        if (targetPageIndex + 1 != commandingPageIndex) {
+                            updatePageTabPosition(tabFolder, page, commandingPageIndex, targetPageIndex);
+                        }
+                        break;
+                    case BEFORE:
+                        if (commandingPageIndex + 1 != targetPageIndex) {
+                            updatePageTabPosition(tabFolder, page, commandingPageIndex, targetPageIndex);
+                        }
+                        break;
+                    case REPLACE:
+                        editor.removePage(targetPageIndex);
+                        commandingPageIndex = pages.indexOf(page);
+                        int targetPageIndexAfterRemoval = targetPageIndex > 0 && targetPageIndex >= pages.size() ? targetPageIndex - 1 : targetPageIndex;
+                        updatePageTabPosition(tabFolder, page, commandingPageIndex, targetPageIndexAfterRemoval);
+                        break;
+                    default:
+                        break;
+                    }
+                }
+                tabFolder.getParent().redraw();
+                tabFolder.getParent().layout();
+                editor.setFocus();
+                editor.setActivePage(activePage);
+            }
+        });
+
+    }
+
+    /**
+     * Execute the page removal command for the given page.
+     * 
+     * @param pageUpdateCommand
+     *            the command containing removal information.
+     * @param editor
+     *            the editor calling for a page removal..
+     * @param page
+     *            the page that will be removed from editor.
+     */
+    private void executeRemoveCommand(RemovePageCommand pageUpdateCommand, SessionEditor editor, AbstractSessionEditorPage page) {
+        PlatformUI.getWorkbench().getDisplay().asyncExec(() -> {
+            editor.removePage(editor.pages.indexOf(page));
+        });
+    }
+
+    /**
+     * Execute the tab renaming command for the given page.
+     * 
+     * @param pageUpdateCommand
+     *            the command containing rename information.
+     * @param editor
+     *            the editor calling for a page tab renaming.
+     * @param page
+     *            the page that will have its tab renamed.
+     */
+    private void executeRenameCommand(RenameTabLabelCommand pageUpdateCommand, SessionEditor editor, AbstractSessionEditorPage page) {
+        PlatformUI.getWorkbench().getDisplay().asyncExec(() -> {
+            Composite container = editor.getContainer();
+            if (container instanceof CTabFolder) {
+                Vector<Object> pages = editor.pages;
+                int index = pages.indexOf(page);
+                if (index != -1) {
+                    CTabFolder tabFolder = (CTabFolder) container;
+                    CTabItem tabItem = tabFolder.getItem(index);
+                    tabItem.setText(pageUpdateCommand.getNewLabel());
+                    tabFolder.getParent().layout();
+                }
+            }
+        });
+    }
 }
diff --git a/plugins/org.eclipse.sirius.ui.editor/src/org/eclipse/sirius/ui/editor/api/pages/AbstractSessionEditorPage.java b/plugins/org.eclipse.sirius.ui.editor/src/org/eclipse/sirius/ui/editor/api/pages/AbstractSessionEditorPage.java
index 9fb62a7af6..63a6b9e422 100644
--- a/plugins/org.eclipse.sirius.ui.editor/src/org/eclipse/sirius/ui/editor/api/pages/AbstractSessionEditorPage.java
+++ b/plugins/org.eclipse.sirius.ui.editor/src/org/eclipse/sirius/ui/editor/api/pages/AbstractSessionEditorPage.java
@@ -11,12 +11,14 @@
 
 package org.eclipse.sirius.ui.editor.api.pages;
 
+import org.eclipse.emf.transaction.ResourceSetChangeEvent;
 import org.eclipse.sirius.ui.editor.api.pages.PageProviderRegistry.PositioningKind;
+import org.eclipse.sirius.ui.editor.api.pages.PageUpdateCommandBuilder.PageUpdateCommand;
 import org.eclipse.ui.forms.editor.FormEditor;
 import org.eclipse.ui.forms.editor.FormPage;
 
 /**
- * Custom page provided to aird editor must extends this class.
+ * Custom page provided to session editor must extends this class.
  * 
  * @author <a href="mailto:pierre.guilet@obeo.fr">Pierre Guilet</a>
  *
@@ -68,4 +70,18 @@ public abstract class AbstractSessionEditorPage extends FormPage {
      */
     public abstract PositioningKind getPositioning();
 
+    /**
+     * This method notifies when a {@link ResourceSetChangeEvent} occurs on
+     * the*session's resource set of the session editor containing your page. If
+     * some* change must be done to the page at editor'slevel, you can return a
+     * list*of {@link PageUpdateCommand}to do so. The command must be provided
+     * by* using the factory {@link PageUpdateCommand }.**
+     * 
+     * @param resourceSetChangeEvent
+     *            the event that occurred.*@return an optional
+     *            {@link PageUpdateCommand} the editor should execute.* It can
+     *            be null.
+     */
+    public abstract PageUpdateCommand notifyAndGetUpdateCommands(ResourceSetChangeEvent resourceSetChangeEvent);
+
 }
diff --git a/plugins/org.eclipse.sirius.ui.editor/src/org/eclipse/sirius/ui/editor/api/pages/DefaultSessionEditorPage.java b/plugins/org.eclipse.sirius.ui.editor/src/org/eclipse/sirius/ui/editor/api/pages/DefaultSessionEditorPage.java
index bc1f20a1b0..18785e6691 100644
--- a/plugins/org.eclipse.sirius.ui.editor/src/org/eclipse/sirius/ui/editor/api/pages/DefaultSessionEditorPage.java
+++ b/plugins/org.eclipse.sirius.ui.editor/src/org/eclipse/sirius/ui/editor/api/pages/DefaultSessionEditorPage.java
@@ -20,6 +20,7 @@ import org.eclipse.core.resources.ResourcesPlugin;
 import org.eclipse.core.runtime.IProgressMonitor;
 import org.eclipse.core.runtime.Path;
 import org.eclipse.emf.transaction.RecordingCommand;
+import org.eclipse.emf.transaction.ResourceSetChangeEvent;
 import org.eclipse.jface.action.Action;
 import org.eclipse.jface.action.ToolBarManager;
 import org.eclipse.jface.layout.GridLayoutFactory;
@@ -33,6 +34,7 @@ import org.eclipse.sirius.ui.editor.Messages;
 import org.eclipse.sirius.ui.editor.SessionEditor;
 import org.eclipse.sirius.ui.editor.SessionEditorPlugin;
 import org.eclipse.sirius.ui.editor.api.pages.PageProviderRegistry.PositioningKind;
+import org.eclipse.sirius.ui.editor.api.pages.PageUpdateCommandBuilder.PageUpdateCommand;
 import org.eclipse.sirius.ui.editor.internal.graphicalcomponents.GraphicalSemanticModelsHandler;
 import org.eclipse.sirius.ui.tools.internal.actions.session.CloseSessionsAction;
 import org.eclipse.sirius.ui.tools.internal.graphicalcomponents.GraphicalRepresentationHandler;
@@ -304,7 +306,6 @@ public class DefaultSessionEditorPage extends AbstractSessionEditorPage implemen
         representationSectionClient.setLayout(GridLayoutFactory.swtDefaults().numColumns(2).create());
         representationSectionClient.setLayoutData(new GridData(SWT.FILL, SWT.FILL, true, true));
         representationSection.setClient(representationSectionClient);
-
         GraphicalRepresentationHandlerBuilder graphicalRepresentationHandlerBuilder = new GraphicalRepresentationHandler.GraphicalRepresentationHandlerBuilder(session);
         graphicalRepresentationHandler = graphicalRepresentationHandlerBuilder.activateBrowserWithViewpointAndRepresentationDescriptionInformation().activateGroupingByCheckbox()
                 .activateRepresentationAndViewpointControls().useToolkitToCreateGraphicComponents(toolkit).activateShowDisabledViewpointsCheckbox().build();
@@ -389,4 +390,9 @@ public class DefaultSessionEditorPage extends AbstractSessionEditorPage implemen
     public PositioningKind getPositioning() {
         return null;
     }
+
+    @Override
+    public PageUpdateCommand notifyAndGetUpdateCommands(ResourceSetChangeEvent resourceSetChangeEvent) {
+        return null;
+    }
 }
diff --git a/plugins/org.eclipse.sirius.ui.editor/src/org/eclipse/sirius/ui/editor/api/pages/PageProviderRegistry.java b/plugins/org.eclipse.sirius.ui.editor/src/org/eclipse/sirius/ui/editor/api/pages/PageProviderRegistry.java
index c56f6369da..7f6b827122 100644
--- a/plugins/org.eclipse.sirius.ui.editor/src/org/eclipse/sirius/ui/editor/api/pages/PageProviderRegistry.java
+++ b/plugins/org.eclipse.sirius.ui.editor/src/org/eclipse/sirius/ui/editor/api/pages/PageProviderRegistry.java
@@ -39,7 +39,10 @@ public class PageProviderRegistry {
      */
     private final List<PageProvider> pageProviders;
 
-    private final PageOrderer pageOrderer;
+    /**
+     * Components ordering pages regarding positioning information.
+     */
+    private PageOrderer pageOrderer;
 
     /**
      * This enum specifies positioning type to apply when initializing an
@@ -144,7 +147,6 @@ public class PageProviderRegistry {
     public List<AbstractSessionEditorPage> getPagesOrdered(SessionEditor editor, Session session, List<AbstractSessionEditorPage> displayedPages) {
         List<AbstractSessionEditorPage> pagesOrdered = pageOrderer.getOrderedPages(pageProviders, editor, displayedPages);
         return pagesOrdered;
-
     }
 
 }
diff --git a/plugins/org.eclipse.sirius.ui.editor/src/org/eclipse/sirius/ui/editor/api/pages/PageUpdateCommandBuilder.java b/plugins/org.eclipse.sirius.ui.editor/src/org/eclipse/sirius/ui/editor/api/pages/PageUpdateCommandBuilder.java
new file mode 100644
index 0000000000..f2646c6d66
--- /dev/null
+++ b/plugins/org.eclipse.sirius.ui.editor/src/org/eclipse/sirius/ui/editor/api/pages/PageUpdateCommandBuilder.java
@@ -0,0 +1,168 @@
+/*******************************************************************************
+ * Copyright (c) 2017 Obeo
+ * All rights reserved. This program and the accompanying materials
+ * are made available under the terms of the Eclipse Public License v1.0
+ * which accompanies this distribution, and is available at
+ * http://www.eclipse.org/legal/epl-v10.html
+ *
+ * Contributors:
+ *     Obeo - initial API and implementation
+ *******************************************************************************/
+package org.eclipse.sirius.ui.editor.api.pages;
+
+import org.eclipse.sirius.ui.editor.SessionEditor;
+import org.eclipse.sirius.ui.editor.api.pages.PageProviderRegistry.PositioningKind;
+import org.eclipse.sirius.ui.editor.internal.pages.RemovePageCommand;
+import org.eclipse.sirius.ui.editor.internal.pages.RenameTabLabelCommand;
+import org.eclipse.sirius.ui.editor.internal.pages.ReorderPageCommand;
+
+/**
+ * Provides commands for {@link AbstractSessionEditorPage} pages to tell owner
+ * editor to update it.
+ * 
+ * @author <a href="mailto:pierre.guilet@obeo.fr">Pierre Guilet</a>
+ *
+ */
+public class PageUpdateCommandBuilder {
+    /**
+     * Component providing commands to execute from a {@link SessionEditor}.
+     * 
+     * @author <a href="mailto:pierre.guilet@obeo.fr">Pierre Guilet</a>
+     *
+     */
+    public class PageUpdateCommand {
+        /**
+         * This command remove the page providing it from its editor.
+         */
+        RemovePageCommand removeCommand;
+
+        /**
+         * This command rename the page's tab of its editor.
+         */
+        RenameTabLabelCommand renameCommand;
+
+        /**
+         * This command reorder the page in its editor to a new location.
+         */
+        ReorderPageCommand reorderCommand;
+
+        /**
+         * Returns the command to remove the page providing it from its editor.
+         * 
+         * @return the command to remove the page providing it from its editor.
+         */
+        public RemovePageCommand getRemoveCommand() {
+            return removeCommand;
+        }
+
+        /**
+         * Returns the command to rename the page's tab of its editor.
+         * 
+         * @return the command to rename the page's tab of its editor.
+         */
+        public RenameTabLabelCommand getRenameCommand() {
+            return renameCommand;
+        }
+
+        /**
+         * Returns the command to reorder the page in its editor to a new
+         * location.
+         * 
+         * @return the command to reorder the page in its editor to a new
+         *         location.
+         */
+        public ReorderPageCommand getReorderCommand() {
+            return reorderCommand;
+        }
+
+        /**
+         * Sets the command to rename the page's tab of its editor.
+         * 
+         * @param renameCommand
+         *            the command to rename the page's tab of its editor.
+         */
+        public void setRenameCommand(RenameTabLabelCommand renameCommand) {
+            this.renameCommand = renameCommand;
+        }
+
+        /**
+         * Sets the command to remove the page providing it from its editor.
+         * 
+         * @param removePageCommand
+         *            the command to remove the page providing it from its
+         *            editor.
+         */
+        public void setRemoveCommand(RemovePageCommand removePageCommand) {
+            this.removeCommand = removePageCommand;
+        }
+
+        /**
+         * Sets the command to reorder the page in its editor to a new location.
+         * 
+         * @param reorderCommand
+         *            the command to reorder the page in its editor to a new
+         *            location.
+         */
+        public void setReorderCommand(ReorderPageCommand reorderCommand) {
+            this.reorderCommand = reorderCommand;
+        }
+    }
+
+    /**
+     * Component providing commands to execute from a {@link SessionEditor}.
+     */
+    PageUpdateCommand pageUpdateCommand;
+
+    /**
+     * Initialize the commands builder.
+     */
+    public PageUpdateCommandBuilder() {
+        pageUpdateCommand = new PageUpdateCommand();
+    }
+
+    /**
+     * Creates a command to rename the page's tab with the given label.
+     * 
+     * @param newLabel
+     *            the new tab label.
+     * @return the command builder.
+     */
+    public PageUpdateCommandBuilder renameTab(String newLabel) {
+        pageUpdateCommand.setRenameCommand(new RenameTabLabelCommand(newLabel));
+        return this;
+    }
+
+    /**
+     * Creates a command to remove the page from its editor.
+     * 
+     * @return the command builder.
+     */
+    public PageUpdateCommandBuilder removePage() {
+        pageUpdateCommand.setRemoveCommand(new RemovePageCommand());
+        return this;
+    }
+
+    /**
+     * Creates a command to reorder the page regarding the given location
+     * information.
+     * 
+     * @param positioningKind
+     *            the kind of positioning to achieve.
+     * @param targetPageId
+     *            the target page id to place this page relatively to.
+     * @return the command builder.
+     */
+    public PageUpdateCommandBuilder reorderPage(PositioningKind positioningKind, String targetPageId) {
+        pageUpdateCommand.setReorderCommand(new ReorderPageCommand(positioningKind, targetPageId));
+        return this;
+    }
+
+    /**
+     * Build the command containing all commands to execute.
+     * 
+     * @return the command containing all commands to execute.
+     */
+    public PageUpdateCommand build() {
+        return pageUpdateCommand;
+    }
+}
diff --git a/plugins/org.eclipse.sirius.ui.editor/src/org/eclipse/sirius/ui/editor/internal/graphicalcomponents/GraphicalSemanticModelsHandler.java b/plugins/org.eclipse.sirius.ui.editor/src/org/eclipse/sirius/ui/editor/internal/graphicalcomponents/GraphicalSemanticModelsHandler.java
index 3fb7b83590..e3ba55d876 100644
--- a/plugins/org.eclipse.sirius.ui.editor/src/org/eclipse/sirius/ui/editor/internal/graphicalcomponents/GraphicalSemanticModelsHandler.java
+++ b/plugins/org.eclipse.sirius.ui.editor/src/org/eclipse/sirius/ui/editor/internal/graphicalcomponents/GraphicalSemanticModelsHandler.java
@@ -409,22 +409,23 @@ public class GraphicalSemanticModelsHandler implements SessionListener, SessionM
                 site.getShell().getDisplay().asyncExec(new Runnable() {
                     @Override
                     public void run() {
-
-                        // Try to select the last affected objects.
-                        Command mostRecentCommand = ((CommandStack) event.getSource()).getMostRecentCommand();
-                        if (mostRecentCommand != null) {
-                            Collection<?> affectedObjects = mostRecentCommand.getAffectedObjects();
-                            if (!affectedObjects.isEmpty()) {
-                                setSelectionToViewer(affectedObjects);
-                            } else {
-                                Tree tree = treeViewer.getTree();
-                                if (!tree.isDisposed() && tree.getItems().length > 0 && !tree.getItem(0).isDisposed()) {
-                                    List<Object> selectionCollection = new ArrayList<Object>();
-                                    selectionCollection.add(tree.getItem(0).getData());
-                                    setSelectionToViewer(selectionCollection);
+                        if (treeViewer != null && !treeViewer.getTree().isDisposed()) {
+                            // Try to select the last affected objects.
+                            Command mostRecentCommand = ((CommandStack) event.getSource()).getMostRecentCommand();
+                            if (mostRecentCommand != null) {
+                                Collection<?> affectedObjects = mostRecentCommand.getAffectedObjects();
+                                if (!affectedObjects.isEmpty()) {
+                                    setSelectionToViewer(affectedObjects);
+                                } else {
+                                    Tree tree = treeViewer.getTree();
+                                    if (!tree.isDisposed() && tree.getItems().length > 0 && !tree.getItem(0).isDisposed()) {
+                                        List<Object> selectionCollection = new ArrayList<Object>();
+                                        selectionCollection.add(tree.getItem(0).getData());
+                                        setSelectionToViewer(selectionCollection);
+                                    }
                                 }
+                                actionBars.updateActionBars();
                             }
-                            actionBars.updateActionBars();
                         }
                     }
                 });
diff --git a/plugins/org.eclipse.sirius.ui.editor/src/org/eclipse/sirius/ui/editor/internal/pages/RemovePageCommand.java b/plugins/org.eclipse.sirius.ui.editor/src/org/eclipse/sirius/ui/editor/internal/pages/RemovePageCommand.java
new file mode 100644
index 0000000000..559fc54b7c
--- /dev/null
+++ b/plugins/org.eclipse.sirius.ui.editor/src/org/eclipse/sirius/ui/editor/internal/pages/RemovePageCommand.java
@@ -0,0 +1,23 @@
+/*******************************************************************************
+ * Copyright (c) 2017 Obeo
+ * All rights reserved. This program and the accompanying materials
+ * are made available under the terms of the Eclipse Public License v1.0
+ * which accompanies this distribution, and is available at
+ * http://www.eclipse.org/legal/epl-v10.html
+ *
+ * Contributors:
+ *     Obeo - initial API and implementation
+ *******************************************************************************/
+package org.eclipse.sirius.ui.editor.internal.pages;
+
+import org.eclipse.sirius.ui.editor.api.pages.AbstractSessionEditorPage;
+
+/**
+ * A command to remove an {@link AbstractSessionEditorPage} from its editor.
+ * 
+ * @author <a href="mailto:pierre.guilet@obeo.fr">Pierre Guilet</a>
+ *
+ */
+public class RemovePageCommand {
+
+}
diff --git a/plugins/org.eclipse.sirius.ui.editor/src/org/eclipse/sirius/ui/editor/internal/pages/RenameTabLabelCommand.java b/plugins/org.eclipse.sirius.ui.editor/src/org/eclipse/sirius/ui/editor/internal/pages/RenameTabLabelCommand.java
new file mode 100644
index 0000000000..1f61345964
--- /dev/null
+++ b/plugins/org.eclipse.sirius.ui.editor/src/org/eclipse/sirius/ui/editor/internal/pages/RenameTabLabelCommand.java
@@ -0,0 +1,44 @@
+/*******************************************************************************
+ * Copyright (c) 2017 Obeo
+ * All rights reserved. This program and the accompanying materials
+ * are made available under the terms of the Eclipse Public License v1.0
+ * which accompanies this distribution, and is available at
+ * http://www.eclipse.org/legal/epl-v10.html
+ *
+ * Contributors:
+ *     Obeo - initial API and implementation
+ *******************************************************************************/
+package org.eclipse.sirius.ui.editor.internal.pages;
+
+/**
+ * A command refreshing the tab label of a multi-page editor's page.
+ * 
+ * @author <a href="mailto:pierre.guilet@obeo.fr">Pierre Guilet</a>
+ *
+ */
+public class RenameTabLabelCommand {
+
+    /**
+     * The label to use when renaming the tab.
+     */
+    private String newLabel;
+
+    /**
+     * Initialize the command with required information.
+     * 
+     * @param newLabel
+     *            the label to use when renaming the tab.
+     */
+    public RenameTabLabelCommand(String newLabel) {
+        this.newLabel = newLabel;
+    }
+
+    /**
+     * Returns the label to use when renaming the tab.
+     * 
+     * @return the label to use when renaming the tab.
+     */
+    public String getNewLabel() {
+        return newLabel;
+    }
+}
diff --git a/plugins/org.eclipse.sirius.ui.editor/src/org/eclipse/sirius/ui/editor/internal/pages/ReorderPageCommand.java b/plugins/org.eclipse.sirius.ui.editor/src/org/eclipse/sirius/ui/editor/internal/pages/ReorderPageCommand.java
new file mode 100644
index 0000000000..ec2101e493
--- /dev/null
+++ b/plugins/org.eclipse.sirius.ui.editor/src/org/eclipse/sirius/ui/editor/internal/pages/ReorderPageCommand.java
@@ -0,0 +1,65 @@
+/*******************************************************************************
+ * Copyright (c) 2017 Obeo
+ * All rights reserved. This program and the accompanying materials
+ * are made available under the terms of the Eclipse Public License v1.0
+ * which accompanies this distribution, and is available at
+ * http://www.eclipse.org/legal/epl-v10.html
+ *
+ * Contributors:
+ *     Obeo - initial API and implementation
+ *******************************************************************************/
+package org.eclipse.sirius.ui.editor.internal.pages;
+
+import org.eclipse.sirius.ui.editor.api.pages.PageProviderRegistry.PositioningKind;
+
+/**
+ * A command to reorder a page to another location identified by a page id among
+ * its parent editor pages.
+ * 
+ * @author <a href="mailto:pierre.guilet@obeo.fr">Pierre Guilet</a>
+ *
+ */
+public class ReorderPageCommand {
+
+    /**
+     * The kind of positioning to achieve.
+     */
+    PositioningKind positioningKind;
+
+    /**
+     * The id of the page to be placed relatively to.
+     */
+    String targetPageId;
+
+    /**
+     * Initialize the command with required information.
+     * 
+     * @param positioningKind
+     *            the kind of positioning to achieve.
+     * @param targetPageId
+     *            the id of the page to be placed relatively to.
+     */
+    public ReorderPageCommand(PositioningKind positioningKind, String targetPageId) {
+        super();
+        this.positioningKind = positioningKind;
+        this.targetPageId = targetPageId;
+    }
+
+    /**
+     * Returns the id of the page to be placed relatively to.
+     * 
+     * @return the id of the page to be placed relatively to.
+     */
+    public String getTargetPageId() {
+        return targetPageId;
+    }
+
+    /**
+     * Returns the kind of positioning to achieve.
+     * 
+     * @return the kind of positioning to achieve.
+     */
+    public PositioningKind getPositioningKind() {
+        return positioningKind;
+    }
+}
diff --git a/plugins/org.eclipse.sirius.ui/src/org/eclipse/sirius/ui/tools/internal/graphicalcomponents/GraphicalRepresentationHandler.java b/plugins/org.eclipse.sirius.ui/src/org/eclipse/sirius/ui/tools/internal/graphicalcomponents/GraphicalRepresentationHandler.java
index 51fac9452b..897fe0d854 100644
--- a/plugins/org.eclipse.sirius.ui/src/org/eclipse/sirius/ui/tools/internal/graphicalcomponents/GraphicalRepresentationHandler.java
+++ b/plugins/org.eclipse.sirius.ui/src/org/eclipse/sirius/ui/tools/internal/graphicalcomponents/GraphicalRepresentationHandler.java
@@ -159,7 +159,7 @@ public class GraphicalRepresentationHandler implements SessionManagerListener {
                         // a model may have been added/removed from the model so we have to update content that is
                         // relative to loaded models.
                         PlatformUI.getWorkbench().getDisplay().asyncExec(() -> {
-                            if (!treeViewer.getTree().isDisposed()) {
+                            if (treeViewer != null && !treeViewer.getTree().isDisposed()) {
                                 initInput();
                             }
                         });
@@ -944,9 +944,11 @@ public class GraphicalRepresentationHandler implements SessionManagerListener {
             return viewpointItemImpl.getViewpoint();
         });
         ViewpointHelper.handleViewpointActivation(session, viewpoints.collect(Collectors.toSet()), enable, true);
-        treeViewer.getTree().setRedraw(true);
-        treeViewer.refresh();
-        treeViewer.setSelection(new StructuredSelection(viewpointsToActivate.stream().collect(Collectors.toList())));
+        if (treeViewer != null && !treeViewer.getTree().isDisposed()) {
+            treeViewer.getTree().setRedraw(true);
+            treeViewer.refresh();
+            treeViewer.setSelection(new StructuredSelection(viewpointsToActivate.stream().collect(Collectors.toList())));
+        }
     }
 
     /**