Section 9.5. Delayed Changed Events

9.5. Delayed Changed Events

Eclipse uses lazy initializationonly load a plug-in when it is needed. Lazy initialization presents a problem for plug-ins that need to track changes. How does a plug-in track changes when it is not loaded?

Eclipse solves this problem by queuing change events for a plug-in that is not loaded. When the plug-in is loaded, it receives a single resource change event containing the union of the changes that have occurred during the time it was not active. To receive this event, your plug-in must register to be a save participant when it is started up, as follows.

public static void addSaveParticipant() {    ISaveParticipant saveParticipant = new ISaveParticipant(){       public void saving(ISaveContext context)          throws CoreException       {          // Save any model state here.          context.needDelta();       }       public void doneSaving(ISaveContext context) {}       public void prepareToSave(ISaveContext context)         throws CoreException {}       public void rollback(ISaveContext context) {}    };    ISavedState savedState;    try {       savedState = ResourcesPlugin          .getWorkspace()          .addSaveParticipant  (             FavoritesPlugin.getDefault(),             saveParticipant);    }    catch (CoreException e) {       FavoritesLog.logError(e);       // Recover if necessary.       return;    }    if (savedState != null)       savedState.processResourceChangeEvents(          FavoritesManager.getManager()); } 

Tip

Even though Eclipse is based on lazy plug-in initialization, it does provide a mechanism for plug-ins to start when the workbench itself starts. To activate at startup, the plug-in must extend the org.eclipse.ui.startup extension point and implement the org.eclipse.ui. IStartup interface. Once the plug-in is started, the workbench will call the plug-in's earlyStartup() method (see Section 3.4.2, Early plug-in startup, on page 114). A workbench preference option gives the user the ability to prevent a plug-in from starting early, so make sure that if your plug-in takes advantage of this extension point, it degrades gracefully in the event that it is not started early.