In general, such components need to know when the client is about + * to enter a place so that they can subscribe if necessary or at least + * extract information about the place. They also need to know when a + * client has left a place so that they can unsubscribe and clean up after + * themselves. This is the information that the place view interface makes + * available to them in a decoupled way. + * + *
The part of the client implementation that is responsible for the
+ * main user interface can act as a location observer, and it can make use
+ * of {@link PlaceViewUtil} to dispatch notification of place changes to
+ * every PlaceView implementing user interface element in the
+ * user interface hierarchy with calls to {@link
+ * PlaceViewUtil#dispatchWillEnterPlace} and {@link
+ * PlaceViewUtil#dispatchDidLeavePlace}. These functions traverse the UI
+ * hierarchy (starting with the element provided which would generally be
+ * the top-level UI element, and dispatch calls to {@link #willEnterPlace}
+ * and {@link #willLeavePlace} respectively on any UI element they find
+ * that implements PlaceView.
+ *
+ *
By doing this, the client code can simply create place-sensitive
+ * user interface elements and stick them in the user interface and
+ * essentially forget about them, knowing that they will all be notified
+ * of place entering and exiting by virtue of the single dispatching
+ * calls. It is useful to note that place-sensitive user interface
+ * elements will also generally need a reference to the {@link
+ * PartyContext} derivative in use by the client, but those are best
+ * supplied at construct time.
+ */
+public interface PlaceView
+{
+ /**
+ * Called when the client has entered a place and is about to display
+ * the user interface for that place.
+ *
+ * @param plobj the place object that was just entered.
+ */
+ public void willEnterPlace (PlaceObject plobj);
+
+ /**
+ * Called after the client has left a place and needs to clean up
+ * after the user interface that was displaying that place.
+ *
+ * @param plobj the place object that was just left.
+ */
+ public void didLeavePlace (PlaceObject plobj);
+}
diff --git a/src/java/com/threerings/crowd/client/PlaceViewUtil.java b/src/java/com/threerings/crowd/client/PlaceViewUtil.java
new file mode 100644
index 000000000..2f87f0b82
--- /dev/null
+++ b/src/java/com/threerings/crowd/client/PlaceViewUtil.java
@@ -0,0 +1,85 @@
+//
+// $Id: PlaceViewUtil.java,v 1.1 2001/10/04 20:02:49 mdb Exp $
+
+package com.threerings.cocktail.party.util;
+
+import java.awt.Component;
+import java.awt.Container;
+
+import com.threerings.cocktail.party.Log;
+import com.threerings.cocktail.party.data.PlaceObject;
+
+/**
+ * Provides a mechanism for dispatching notifications to all user
+ * interface elements in a hierarchy that implement the {@link PlaceView}
+ * interface. Look at the documentation for {@link PlaceView} for more
+ * explanation.
+ */
+public class PlaceViewUtil
+{
+ /**
+ * Dispatches a call to {@link PlaceView#willEnterPlace} to all UI
+ * elements in the hierarchy rooted at the component provided via the
+ * root parameter.
+ *
+ * @param root the component at which to start traversing the UI
+ * hierarchy.
+ * @param plobj the place object that is about to be entered.
+ */
+ public static void dispatchWillEnterPlace (
+ Component root, PlaceObject plobj)
+ {
+ // dispatch the call on this component if it implements PlaceView
+ if (root instanceof PlaceView) {
+ try {
+ ((PlaceView)root).willEnterPlace(plobj);
+ } catch (Exception e) {
+ Log.warning("Component choked on willEnterPlace() " +
+ "[component=" + root + ", plobj=" + plobj + "].");
+ Log.logStackTrace(e);
+ }
+ }
+
+ // now traverse all of this component's children
+ if (root instanceof Container) {
+ Container cont = (Container)root;
+ int ccount = cont.getComponentCount();
+ for (int i = 0; i < ccount; i++) {
+ dispatchWillEnterPlace(cont.getComponent(i), plobj);
+ }
+ }
+ }
+
+ /**
+ * Dispatches a call to {@link PlaceView#didLeavePlace} to all UI
+ * elements in the hierarchy rooted at the component provided via the
+ * root parameter.
+ *
+ * @param root the component at which to start traversing the UI
+ * hierarchy.
+ * @param plobj the place object that is about to be entered.
+ */
+ public static void dispatchDidLeavePlace (
+ Component root, PlaceObject plobj)
+ {
+ // dispatch the call on this component if it implements PlaceView
+ if (root instanceof PlaceView) {
+ try {
+ ((PlaceView)root).didLeavePlace(plobj);
+ } catch (Exception e) {
+ Log.warning("Component choked on didLeavePlace() " +
+ "[component=" + root + ", plobj=" + plobj + "].");
+ Log.logStackTrace(e);
+ }
+ }
+
+ // now traverse all of this component's children
+ if (root instanceof Container) {
+ Container cont = (Container)root;
+ int ccount = cont.getComponentCount();
+ for (int i = 0; i < ccount; i++) {
+ dispatchDidLeavePlace(cont.getComponent(i), plobj);
+ }
+ }
+ }
+}