Changes between Version 18 and Version 19 of PluginDevelopmentGuide

Timestamp:

16.04.2013 01:44:28 (12 years ago)

Author:

jri

Comment:

Listen to DeepaMehta Core events

PluginDevelopmentGuide

@@ -670 +670 @@
 </project>
 }}}
+
+=== Listen to DeepaMehta Core events ===
+
+In particular situations the DeepaMehta Core fires events, e.g. before and after it creates a new topic in the database. Your plugin can listen to these events and react in its own way.
+
+Listening to a DeepaMehta Core event means implementing the corresponding listener interface. A listener interface consist of just one method: the //listener method//. That method is called by the DeepaMehta Core when the event is fired. The listener interfaces are located in package `de.deepamehta.core.service.event`.
+
+To listen to a DeepaMehta Core event, in the plugin main class you must:
+
+    * Import the listener interface.
+    * Declare the plugin main class implements that interface.
+    * Implement the listener method. Use the `@Override` annotation.
+    * Import the classes appearing in the listener method arguments.
+
+Example:
+
+{{{
+#!java
+package org.mydomain.deepamehta4.mycoolplugin;
+
+import de.deepamehta.core.Topic;
+import de.deepamehta.core.model.TopicModel;
+import de.deepamehta.core.osgi.PluginActivator;
+import de.deepamehta.core.service.ClientState;
+import de.deepamehta.core.service.Directives;
+import de.deepamehta.core.service.event.PostCreateTopicListener;
+import de.deepamehta.core.service.event.PostUpdateTopicListener;
+
+import java.util.logging.Logger;
+
+
+
+public class MyCoolPlugin extends PluginActivator implements PostCreateTopicListener, PostUpdateTopicListener {
+
+    private Logger log = Logger.getLogger(getClass().getName());
+
+    @Override
+    public void postCreateTopic(Topic topic, ClientState clientState, Directives directives) {
+        log.info("### Topic created: " + topic);
+    }
+
+    @Override
+    public void postUpdateTopic(Topic topic, TopicModel newModel, TopicModel oldModel, ClientState clientState,
+                                                                                       Directives directives) {
+        log.info("### Topic updated: " + topic + "\nOld topic: " + oldModel);
+    }
+}
+}}}
+
+This example plugin listens to 2 DeepaMehta Core events: `POST_CREATE_TOPIC` and `POST_UPDATE_TOPIC`.
+
+These particular events are fired //after// the DeepaMehta Core has created resp. updated a topic. The DeepaMehta Core passes the created/updated topic to the respective listener method. In case of "update" the previous topic content (`oldModel`) is also passed to enable the plugin to investigate what exactly has changed.
+
+The example plugin just logs the created resp. updated topic. In case of "update" the previous topic content is logged as well.
+
+A [[DeepaMehtaCoreEvents|list of all DeepaMehta Core events]] is available in the reference section.