[518524] Add deferred refresh and command execution

Aird editor custom pages now can tell the editor to be called for
refresh and page update only when it has focus.

Bug: 518524
Change-Id: Ic141540d1cab6e1fcf8dc83f6cfcbdd5ed09cd5e
Signed-off-by: pguilet <pierre.guilet@obeo.fr>

10 files changed, 252 insertions, 82 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 4bbf77462e..eada1587d0 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
@@ -10,6 +10,8 @@
  *******************************************************************************/
 package org.eclipse.sirius.ui.debug.pages;
 
+import java.util.Optional;
+
 import org.eclipse.emf.transaction.ResourceSetChangeEvent;
 import org.eclipse.jface.layout.GridLayoutFactory;
 import org.eclipse.sirius.business.api.session.Session;
@@ -64,18 +66,23 @@ public class DebugPage extends AbstractSessionEditorPage {
     }
 
     @Override
-    public String getLocationId() {
-        return DefaultSessionEditorPage.PAGE_ID;
+    public Optional<String> getLocationId() {
+        return Optional.of(DefaultSessionEditorPage.PAGE_ID);
+    }
+
+    @Override
+    public Optional<PositioningKind> getPositioning() {
+        return Optional.of(PositioningKind.AFTER);
     }
 
     @Override
-    public PositioningKind getPositioning() {
-        return PositioningKind.AFTER;
+    public Optional<PageUpdateCommand> resourceSetChanged(ResourceSetChangeEvent resourceSetChangeEvent) {
+        return Optional.empty();
     }
 
     @Override
-    public PageUpdateCommand notifyAndGetUpdateCommands(ResourceSetChangeEvent resourceSetChangeEvent) {
-        return null;
+    public Optional<PageUpdateCommand> pageChanged(boolean isVisible) {
+        return Optional.empty();
     }
 
 }
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 d0575a665f..dcb26df6ee 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
@@ -38,4 +38,8 @@ public class DebugPageProvider extends PageProvider {
         return resultMap;
     }
 
+    @Override
+    public boolean provides(String pageId) {
+        return DebugPage.PAGE_ID.equals(pageId);
+    }
 }
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 8f507c360d..85c797fbc6 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
@@ -12,8 +12,10 @@ package org.eclipse.sirius.ui.editor;
 
 import java.lang.reflect.InvocationTargetException;
 import java.text.MessageFormat;
+import java.util.ArrayList;
 import java.util.EventObject;
 import java.util.List;
+import java.util.Optional;
 import java.util.Vector;
 import java.util.stream.Collectors;
 
@@ -29,6 +31,7 @@ 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.NotificationFilter;
 import org.eclipse.emf.transaction.ResourceSetChangeEvent;
 import org.eclipse.emf.transaction.ResourceSetListenerImpl;
 import org.eclipse.jface.dialogs.ErrorDialog;
@@ -93,14 +96,21 @@ public class SessionEditor extends SharedHeaderFormEditor implements ITabbedProp
         @Override
         public void resourceSetChanged(ResourceSetChangeEvent event) {
             int pageCount = SessionEditor.this.getPageCount();
+            List<Runnable> commandsToExecute = new ArrayList<>();
             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);
+                    Optional<NotificationFilter> notificationFilter = customPage.getFilterForPageRequesting();
+                    boolean providePages = event.getNotifications().stream().anyMatch(notification -> notificationFilter.isPresent() ? true : notificationFilter.get().matches(notification));
+                    if (providePages) {
+                        Optional<PageUpdateCommand> updateCommand = customPage.resourceSetChanged(event);
+                        commandsToExecute.addAll(prepareUpdateCommands(customPage, updateCommand));
+                    }
                 }
             }
+            executeCommands(commandsToExecute);
+            updatePages(event);
         }
 
         @Override
@@ -145,17 +155,31 @@ public class SessionEditor extends SharedHeaderFormEditor implements ITabbedProp
 
     @Override
     protected void addPages() {
-        updatePages();
+        updatePages(null);
+    }
+
+    /**
+     * Execute the given command in UI thread.
+     * 
+     * @param commandsToExecute
+     *            the commands to execute.
+     */
+    private void executeCommands(List<Runnable> commandsToExecute) {
+        PlatformUI.getWorkbench().getDisplay().asyncExec(() -> {
+            commandsToExecute.stream().forEach(Runnable::run);
+        });
     }
 
     /**
      * Remove obsolete page, add new pages and reorder all pages currently
      * displayed like the new list.
      * 
+     * @param event
+     * 
      */
-    private void updatePages() {
+    private void updatePages(ResourceSetChangeEvent event) {
         List<AbstractSessionEditorPage> newOrderedPages = pageRegistry.getPagesOrdered(this, session,
-                pages.stream().filter(AbstractSessionEditorPage.class::isInstance).map(AbstractSessionEditorPage.class::cast).collect(Collectors.toList()));
+                pages.stream().filter(AbstractSessionEditorPage.class::isInstance).map(AbstractSessionEditorPage.class::cast).collect(Collectors.toList()), event);
 
         CTabFolder cTabF = (CTabFolder) this.getContainer();
         IFormPage activePage = getActivePageInstance();
@@ -252,12 +276,31 @@ public class SessionEditor extends SharedHeaderFormEditor implements ITabbedProp
 
     @Override
     public void pageProviderChanged() {
-        updatePages();
+        updatePages(null);
     }
 
     @Override
     public void init(IEditorSite site, IEditorInput input) throws PartInitException {
         super.init(site, input);
+        this.addPageChangedListener(event -> {
+            Object selectedPage = event.getSelectedPage();
+            if (selectedPage instanceof AbstractSessionEditorPage) {
+                AbstractSessionEditorPage theSelectedPage = (AbstractSessionEditorPage) selectedPage;
+                Optional<PageUpdateCommand> selectedPageCommand = theSelectedPage.pageChanged(true);
+                List<Runnable> commandsToExecute = new ArrayList<>();
+                commandsToExecute.addAll(prepareUpdateCommands(theSelectedPage, selectedPageCommand));
+                for (Object page : pages) {
+                    if (page instanceof AbstractSessionEditorPage) {
+                        AbstractSessionEditorPage sessionEditorPage = (AbstractSessionEditorPage) page;
+                        if (sessionEditorPage.getIndex() != theSelectedPage.getIndex()) {
+                            Optional<PageUpdateCommand> pageCommand = sessionEditorPage.pageChanged(false);
+                            commandsToExecute.addAll(prepareUpdateCommands(sessionEditorPage, pageCommand));
+                        }
+                    }
+                }
+                executeCommands(commandsToExecute);
+            }
+        });
         IEditorInput editorInput = this.getEditorInput();
         URI sessionResourceURI = null;
         if (editorInput instanceof FileEditorInput) {
@@ -467,36 +510,39 @@ public class SessionEditor extends SharedHeaderFormEditor implements ITabbedProp
     }
 
     /**
-     * Execute the given {@link PageUpdateCommand}. If a remove command is
-     * present, other update command will be ignored.
+     * Prepare all commands as {@link Runnable} from 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) {
+    private List<Runnable> prepareUpdateCommands(AbstractSessionEditorPage customPage, Optional<PageUpdateCommand> updateCommand) {
+        List<Runnable> runnables = new ArrayList<>(2);
+        updateCommand.ifPresent(updateCommandTemp -> {
             boolean removeCommandExecuted = false;
-            if (updateCommand.getRemoveCommand() != null) {
-                executeRemoveCommand(updateCommand.getRemoveCommand(), SessionEditor.this, customPage);
+            if (updateCommandTemp.getRemoveCommand() != null) {
+                runnables.add(prepareRemoveCommand(updateCommandTemp.getRemoveCommand(), SessionEditor.this, customPage));
                 removeCommandExecuted = true;
             }
-            if (!removeCommandExecuted && updateCommand.getReorderCommand() != null) {
-                executeReorderCommand(updateCommand.getReorderCommand(), SessionEditor.this, customPage);
+            if (!removeCommandExecuted && updateCommandTemp.getReorderCommand() != null) {
+                runnables.add(prepareReorderCommand(updateCommandTemp.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);
+            if (!removeCommandExecuted && updateCommandTemp.getRenameCommand() != null) {
+                runnables.add(prepareRenameCommand(updateCommandTemp.getRenameCommand(), SessionEditor.this, customPage));
             } else {
                 SessionEditorPlugin.getPlugin().error(MessageFormat.format(Messages.SessionEditor_PageCommand_Integrity_Error, customPage.getClass().getName()), null);
             }
-        }
+        });
+        return runnables;
     }
 
     /**
-     * Execute the reorder command.
+     * Prepare the reorder command by returning a {@link Runnable}.
      * 
      * @param pageUpdateCommand
      *            the command to execute containing execution information.
@@ -505,13 +551,12 @@ public class SessionEditor extends SharedHeaderFormEditor implements ITabbedProp
      * @param page
      *            the page reordered.
      */
-    private void executeReorderCommand(ReorderPageCommand pageUpdateCommand, SessionEditor editor, AbstractSessionEditorPage page) {
-        PlatformUI.getWorkbench().getDisplay().asyncExec(() -> {
+    private Runnable prepareReorderCommand(ReorderPageCommand pageUpdateCommand, SessionEditor editor, AbstractSessionEditorPage page) {
+        return () -> {
             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) {
@@ -520,7 +565,6 @@ public class SessionEditor extends SharedHeaderFormEditor implements ITabbedProp
                         break;
                     }
                 }
-
                 int commandingPageIndex = pages.indexOf(page);
                 if (commandingPageIndex != -1 && targetPageIndex != -1) {
                     switch (pageUpdateCommand.getPositioningKind()) {
@@ -549,12 +593,12 @@ public class SessionEditor extends SharedHeaderFormEditor implements ITabbedProp
                 editor.setFocus();
                 editor.setActivePage(activePage);
             }
-        });
-
+        };
     }
 
     /**
-     * Execute the page removal command for the given page.
+     * Prepare the page removal command for the given page by returning a
+     * {@link Runnable}.
      * 
      * @param pageUpdateCommand
      *            the command containing removal information.
@@ -563,14 +607,15 @@ public class SessionEditor extends SharedHeaderFormEditor implements ITabbedProp
      * @param page
      *            the page that will be removed from editor.
      */
-    private void executeRemoveCommand(RemovePageCommand pageUpdateCommand, SessionEditor editor, AbstractSessionEditorPage page) {
-        PlatformUI.getWorkbench().getDisplay().asyncExec(() -> {
+    private Runnable prepareRemoveCommand(RemovePageCommand pageUpdateCommand, SessionEditor editor, AbstractSessionEditorPage page) {
+        return () -> {
             editor.removePage(editor.pages.indexOf(page));
-        });
+        };
     }
 
     /**
-     * Execute the tab renaming command for the given page.
+     * Prepare the tab renaming command for the given page by returning a
+     * {@link Runnable}.
      * 
      * @param pageUpdateCommand
      *            the command containing rename information.
@@ -579,8 +624,8 @@ public class SessionEditor extends SharedHeaderFormEditor implements ITabbedProp
      * @param page
      *            the page that will have its tab renamed.
      */
-    private void executeRenameCommand(RenameTabLabelCommand pageUpdateCommand, SessionEditor editor, AbstractSessionEditorPage page) {
-        PlatformUI.getWorkbench().getDisplay().asyncExec(() -> {
+    private Runnable prepareRenameCommand(RenameTabLabelCommand pageUpdateCommand, SessionEditor editor, AbstractSessionEditorPage page) {
+        return () -> {
             Composite container = editor.getContainer();
             if (container instanceof CTabFolder) {
                 Vector<Object> pages = editor.pages;
@@ -592,6 +637,6 @@ public class SessionEditor extends SharedHeaderFormEditor implements ITabbedProp
                     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 63a6b9e422..e7876e4457 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
@@ -11,7 +11,11 @@
 
 package org.eclipse.sirius.ui.editor.api.pages;
 
+import java.util.Optional;
+
+import org.eclipse.emf.transaction.NotificationFilter;
 import org.eclipse.emf.transaction.ResourceSetChangeEvent;
+import org.eclipse.sirius.ui.editor.SessionEditor;
 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;
@@ -57,31 +61,73 @@ public abstract class AbstractSessionEditorPage extends FormPage {
      * page.
      * 
      * @return the id of the page to take in consideration when positioning this
-     *         page.
+     *         page. {@link Optional#empty()} if no positioning is provided.
      */
-    public abstract String getLocationId();
+    public abstract Optional<String> getLocationId();
 
     /**
      * Returns the kind of positioning to apply regarding the target page
      * returned by {@link AbstractSessionEditorPage#getLocationId()}.
      * 
      * @return the kind of positioning to apply regarding the target page
-     *         returned by {@link AbstractSessionEditorPage#getLocationId()}.
+     *         returned by
+     *         {@link AbstractSessionEditorPage#getLocationId()}.{@link Optional#empty()}
+     *         if no positioning is provided.
      */
-    public abstract PositioningKind getPositioning();
+    public abstract Optional<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 }.**
+     * This method notifies you when a {@link ResourceSetChangeEvent} occurs on
+     * the session's resource set of the session editor containing your page. If
+     * some changes must be done to the page at editor's level, you can return a
+     * {@link PageUpdateCommand} built with {@link PageUpdateCommandBuilder} to
+     * do so.
      * 
      * @param resourceSetChangeEvent
-     *            the event that occurred.*@return an optional
-     *            {@link PageUpdateCommand} the editor should execute.* It can
-     *            be null.
+     *            the event that occurred.
+     * @return an {@link PageUpdateCommand} the editor should execute.
+     *         {@link Optional#empty()} if no update should be done.
+     */
+    public abstract Optional<PageUpdateCommand> resourceSetChanged(ResourceSetChangeEvent resourceSetChangeEvent);
+
+    /**
+     * Notifies the page that its visibility status has changed. You can return
+     * a {@link PageUpdateCommand} built with {@link PageUpdateCommandBuilder}
+     * if a page update must be done from session editor owning this page.
+     * 
+     * The method is call with the parameter isVisible to true when the page tab
+     * is selected.
+     * 
+     * The method is call with the parameter isVisible to false when any page
+     * tab except the one of this page is selected.
+     * 
+     * 
+     * @param isVisible
+     *            true if the page has just been made visible. I.e page tab has
+     *            been clicked. False if the page has just been made invisible.
+     *            I.e another page tab has been clicked.
+     * @return a {@link PageUpdateCommand} built with
+     *         {@link PageUpdateCommandBuilder} if a page update must be done
+     *         from session editor owning this page. {@link Optional#empty()} if
+     *         no update must be done.
      */
-    public abstract PageUpdateCommand notifyAndGetUpdateCommands(ResourceSetChangeEvent resourceSetChangeEvent);
+    public abstract Optional<PageUpdateCommand> pageChanged(boolean isVisible);
+
+    /**
+     * Returns a filter that will reduce the call to the method
+     * {@link PageProvider#getPages(SessionEditor)} for better performances.
+     * Without the filter, the method is called when any resource set event
+     * occurs on the editor's session.
+     * 
+     * By default, the {@link NotificationFilter#NOT_TOUCH} filter is provided.
+     * 
+     * @return a filter that will reduce the call to the method
+     *         {@link PageProvider#getPages(SessionEditor)} for better
+     *         performances. {@link Optional#empty()} if no filtering should be
+     *         done.
+     */
+    public Optional<NotificationFilter> getFilterForPageRequesting() {
+        return Optional.of(NotificationFilter.NOT_TOUCH);
+    }
 
 }
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 18785e6691..eac346ead5 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
@@ -13,6 +13,7 @@ package org.eclipse.sirius.ui.editor.api.pages;
 import java.net.MalformedURLException;
 import java.net.URL;
 import java.text.MessageFormat;
+import java.util.Optional;
 import java.util.stream.Collectors;
 
 import org.eclipse.core.resources.IProject;
@@ -382,17 +383,23 @@ public class DefaultSessionEditorPage extends AbstractSessionEditorPage implemen
     }
 
     @Override
-    public String getLocationId() {
-        return null;
+    public Optional<String> getLocationId() {
+        return Optional.empty();
     }
 
     @Override
-    public PositioningKind getPositioning() {
-        return null;
+    public Optional<PositioningKind> getPositioning() {
+        return Optional.empty();
     }
 
     @Override
-    public PageUpdateCommand notifyAndGetUpdateCommands(ResourceSetChangeEvent resourceSetChangeEvent) {
-        return null;
+    public Optional<PageUpdateCommand> resourceSetChanged(ResourceSetChangeEvent resourceSetChangeEvent) {
+        return Optional.empty();
     }
+
+    @Override
+    public Optional<PageUpdateCommand> pageChanged(boolean isVisible) {
+        return Optional.empty();
+    }
+
 }
diff --git a/plugins/org.eclipse.sirius.ui.editor/src/org/eclipse/sirius/ui/editor/api/pages/PageProvider.java b/plugins/org.eclipse.sirius.ui.editor/src/org/eclipse/sirius/ui/editor/api/pages/PageProvider.java
index 9860d85e75..7f1997f9d4 100644
--- a/plugins/org.eclipse.sirius.ui.editor/src/org/eclipse/sirius/ui/editor/api/pages/PageProvider.java
+++ b/plugins/org.eclipse.sirius.ui.editor/src/org/eclipse/sirius/ui/editor/api/pages/PageProvider.java
@@ -13,6 +13,7 @@ package org.eclipse.sirius.ui.editor.api.pages;
 import java.util.Map;
 import java.util.function.Supplier;
 
+import org.eclipse.emf.transaction.NotificationFilter;
 import org.eclipse.sirius.ui.editor.SessionEditor;
 import org.eclipse.ui.part.MultiPageEditorPart;
 
@@ -39,4 +40,31 @@ public abstract class PageProvider {
      *         in a multi-page editor.
      */
     public abstract Map<String, Supplier<AbstractSessionEditorPage>> getPages(SessionEditor editor);
+
+    /**
+     * Returns a filter that will reduce the call to the method
+     * {@link PageProvider#getPages(SessionEditor)} for better performances.
+     * Without the filter, the method is called when any resource set event
+     * occurs on the editor's session.
+     * 
+     * By default, the {@link NotificationFilter#NOT_TOUCH} filter is provided.
+     * 
+     * @return a filter that will reduce the call to the method
+     *         {@link PageProvider#getPages(SessionEditor)} for better
+     *         performances.
+     */
+    public NotificationFilter getFilterForPageRequesting() {
+        return NotificationFilter.NOT_TOUCH;
+    }
+
+    /**
+     * Returns true if this provider provides pages with the given id.
+     * 
+     * @param pageId
+     *            the page's id from which we want to know if this provider
+     *            provides pages with this id.
+     * @return true if this provider provides pages with the given id. False
+     *         otherwise.
+     */
+    public abstract boolean provides(String pageId);
 }
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 7f6b827122..a52d512742 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
@@ -15,6 +15,7 @@ import java.util.List;
 import java.util.Set;
 import java.util.concurrent.CopyOnWriteArrayList;
 
+import org.eclipse.emf.transaction.ResourceSetChangeEvent;
 import org.eclipse.sirius.business.api.session.Session;
 import org.eclipse.sirius.ui.editor.SessionEditor;
 import org.eclipse.sirius.ui.editor.internal.pages.PageOrderer;
@@ -139,13 +140,15 @@ public class PageProviderRegistry {
      *            the aird editor's session from which page request is done.
      * @param displayedPages
      *            pages already dysplayed by the editor.
+     * @param event
+     *            the event triggering the call to this method. Can be null.
      * @return a list of {@link AbstractSessionEditorPage} in the order computed
      *         from all their location information retrieved from their parent
      *         creators {@link PageProvider}. Obsolete pages are not returned.
      *         New available pages fitting current context are returned.
      */
-    public List<AbstractSessionEditorPage> getPagesOrdered(SessionEditor editor, Session session, List<AbstractSessionEditorPage> displayedPages) {
-        List<AbstractSessionEditorPage> pagesOrdered = pageOrderer.getOrderedPages(pageProviders, editor, displayedPages);
+    public List<AbstractSessionEditorPage> getPagesOrdered(SessionEditor editor, Session session, List<AbstractSessionEditorPage> displayedPages, ResourceSetChangeEvent event) {
+        List<AbstractSessionEditorPage> pagesOrdered = pageOrderer.getOrderedPages(pageProviders, editor, displayedPages, event);
         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
index f2646c6d66..69f4af52b9 100644
--- 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
@@ -30,7 +30,7 @@ public class PageUpdateCommandBuilder {
      * @author <a href="mailto:pierre.guilet@obeo.fr">Pierre Guilet</a>
      *
      */
-    public class PageUpdateCommand {
+    public final class PageUpdateCommand {
         /**
          * This command remove the page providing it from its editor.
          */
@@ -46,6 +46,9 @@ public class PageUpdateCommandBuilder {
          */
         ReorderPageCommand reorderCommand;
 
+        private PageUpdateCommand() {
+        }
+
         /**
          * Returns the command to remove the page providing it from its editor.
          * 
diff --git a/plugins/org.eclipse.sirius.ui.editor/src/org/eclipse/sirius/ui/editor/internal/pages/DefaultPageProvider.java b/plugins/org.eclipse.sirius.ui.editor/src/org/eclipse/sirius/ui/editor/internal/pages/DefaultPageProvider.java
index 912b1264f2..faa712a3ac 100644
--- a/plugins/org.eclipse.sirius.ui.editor/src/org/eclipse/sirius/ui/editor/internal/pages/DefaultPageProvider.java
+++ b/plugins/org.eclipse.sirius.ui.editor/src/org/eclipse/sirius/ui/editor/internal/pages/DefaultPageProvider.java
@@ -36,4 +36,9 @@ public class DefaultPageProvider extends PageProvider {
         });
         return resultMap;
     }
+
+    @Override
+    public boolean provides(String pageId) {
+        return DefaultSessionEditorPage.PAGE_ID.equals(pageId);
+    }
 }
diff --git a/plugins/org.eclipse.sirius.ui.editor/src/org/eclipse/sirius/ui/editor/internal/pages/PageOrderer.java b/plugins/org.eclipse.sirius.ui.editor/src/org/eclipse/sirius/ui/editor/internal/pages/PageOrderer.java
index bc2f07121c..4a081184dd 100644
--- a/plugins/org.eclipse.sirius.ui.editor/src/org/eclipse/sirius/ui/editor/internal/pages/PageOrderer.java
+++ b/plugins/org.eclipse.sirius.ui.editor/src/org/eclipse/sirius/ui/editor/internal/pages/PageOrderer.java
@@ -11,16 +11,21 @@
 package org.eclipse.sirius.ui.editor.internal.pages;
 
 import java.util.ArrayList;
+import java.util.Collections;
 import java.util.HashMap;
 import java.util.HashSet;
 import java.util.LinkedList;
 import java.util.List;
 import java.util.Map;
 import java.util.Map.Entry;
+import java.util.Optional;
 import java.util.Set;
 import java.util.function.Supplier;
 import java.util.stream.Collectors;
 
+import org.eclipse.emf.common.notify.Notification;
+import org.eclipse.emf.transaction.NotificationFilter;
+import org.eclipse.emf.transaction.ResourceSetChangeEvent;
 import org.eclipse.sirius.ui.editor.SessionEditor;
 import org.eclipse.sirius.ui.editor.api.pages.AbstractSessionEditorPage;
 import org.eclipse.sirius.ui.editor.api.pages.PageProvider;
@@ -99,14 +104,17 @@ public class PageOrderer {
      * 
      * @param alreadyInitializedPages
      *            the pages the editor currently contains.
+     * @param event
+     *            the event triggering the call to this method. Can be null.
      * @return all pages the caller should display in the order defined by all
      *         their positioning information.
      */
-    public List<AbstractSessionEditorPage> getOrderedPages(List<PageProvider> pageProviders, SessionEditor editor, List<AbstractSessionEditorPage> alreadyInitializedPages) {
+    public List<AbstractSessionEditorPage> getOrderedPages(List<PageProvider> pageProviders, SessionEditor editor, List<AbstractSessionEditorPage> alreadyInitializedPages,
+            ResourceSetChangeEvent event) {
         List<AbstractSessionEditorPage> pagesToKeep = new ArrayList<>();
         List<PagePositioning> pagePositioningElements = new ArrayList<>();
         Map<String, PagePositioning> pageIdToPageMap = new HashMap<>();
-        initializePagePositioning(pageProviders, editor, alreadyInitializedPages, pagesToKeep, pagePositioningElements, pageIdToPageMap);
+        initializePagePositioning(pageProviders, editor, alreadyInitializedPages, pagesToKeep, pagePositioningElements, pageIdToPageMap, event);
         positionPagesRegardingOthers(pagePositioningElements, pageIdToPageMap);
         Set<PagePositioning> replacedPages = new HashSet<>();
         replacePages(pagePositioningElements, pageIdToPageMap, replacedPages);
@@ -262,26 +270,38 @@ public class PageOrderer {
      * @param pageIdToPageMap
      *            a map of page id to the corresponding {@link PagePositioning}
      *            containing a page to display in the given editor.
+     * @param event
+     *            the event triggering the call to this method. Can be null.
      */
     private void initializePagePositioning(List<PageProvider> pageProviders, SessionEditor editor, List<AbstractSessionEditorPage> alreadyInitializedPages, List<AbstractSessionEditorPage> pagesToKeep,
-            List<PagePositioning> pagePositioningElements, Map<String, PagePositioning> pageIdToPageMap) {
+            List<PagePositioning> pagePositioningElements, Map<String, PagePositioning> pageIdToPageMap, ResourceSetChangeEvent event) {
         Set<String> alreadyInitializedPagesId = alreadyInitializedPages.stream().map(page -> page.getId()).collect(Collectors.toSet());
         for (PageProvider pageProvider : pageProviders) {
-            Map<String, Supplier<AbstractSessionEditorPage>> pagesToAdd = pageProvider.getPages(editor);
-            if (pagesToAdd != null) {
-                // For each page provided by the provider we initialize a
-                // PagePositionning defining the page and the location it
-                // should have regarding other page.
-                for (Entry<String, Supplier<AbstractSessionEditorPage>> pageEntry : pagesToAdd.entrySet()) {
-                    if (!alreadyInitializedPagesId.contains(pageEntry.getKey())) {
-                        AbstractSessionEditorPage page = pageEntry.getValue().get();
-                        PositioningKind positioningKind = page.getPositioning();
-                        String locationId = page.getLocationId();
-                        PagePositioning pagePositioning = new PagePositioning();
-                        pageIdToPageMap.put(page.getId(), pagePositioning);
-                        pagePositioningElements.add(pagePositioning);
-                        setPortsId(positioningKind, locationId, pagePositioning);
-                        pagePositioning.page = page;
+            List<Notification> notifications = event != null ? event.getNotifications() : Collections.emptyList();
+            NotificationFilter filterForInitialCondition = pageProvider.getFilterForPageRequesting();
+            boolean providePages = notifications.isEmpty()
+                    || notifications.stream().anyMatch(notification -> filterForInitialCondition == null ? true : filterForInitialCondition.matches(notification));
+            if (providePages) {
+                Map<String, Supplier<AbstractSessionEditorPage>> pagesToAdd = pageProvider.getPages(editor);
+                if (pagesToAdd != null) {
+                    // For each page provided by the provider we initialize a
+                    // PagePositionning defining the page and the location it
+                    // should have regarding other page.
+                    for (Entry<String, Supplier<AbstractSessionEditorPage>> pageEntry : pagesToAdd.entrySet()) {
+                        if (!alreadyInitializedPagesId.contains(pageEntry.getKey())) {
+                            AbstractSessionEditorPage page = pageEntry.getValue().get();
+
+                            PagePositioning pagePositioning = new PagePositioning();
+                            pageIdToPageMap.put(page.getId(), pagePositioning);
+                            pagePositioningElements.add(pagePositioning);
+                            Optional<PositioningKind> positioningKind = page.getPositioning();
+                            Optional<String> locationId = page.getLocationId();
+                            if (positioningKind.isPresent() && locationId.isPresent()) {
+                                setPortsId(positioningKind.get(), locationId.get(), pagePositioning);
+                            }
+                            pagePositioning.page = page;
+
+                        }
                     }
                 }
             }
@@ -290,13 +310,15 @@ public class PageOrderer {
                 // should be kept, we ask this provider to know if some
                 // additional already initialized pages should be kept.
                 for (AbstractSessionEditorPage page : alreadyInitializedPages) {
-                    if (pagesToAdd.get(page.getId()) != null) {
+                    if (pageProvider.provides(page.getId())) {
                         pagesToKeep.add(page);
-                        PositioningKind positioningKind = page.getPositioning();
-                        String locationId = page.getLocationId();
                         PagePositioning pagePositioning = new PagePositioning();
                         pageIdToPageMap.put(page.getId(), pagePositioning);
-                        setPortsId(positioningKind, locationId, pagePositioning);
+                        Optional<PositioningKind> positioningKind = page.getPositioning();
+                        Optional<String> locationId = page.getLocationId();
+                        if (positioningKind.isPresent() && locationId.isPresent()) {
+                            setPortsId(positioningKind.get(), locationId.get(), pagePositioning);
+                        }
                         pagePositioning.page = page;
                         pagePositioningElements.add(pagePositioning);
                     }