Created a mechanism for dispatching notifications to user interface

elements when the client enters and leaves a place.


git-svn-id: svn+ssh://src.earth.threerings.net/narya/trunk@394 542714f4-19e9-0310-aa3c-eee0fc999fb1

src/java/com/threerings/crowd/client/PlaceView.java

@@ -0,0 +1,58 @@
+//
+// $Id: PlaceView.java,v 1.1 2001/10/04 20:02:49 mdb Exp $
+
+package com.threerings.cocktail.party.util;
+
+import com.threerings.cocktail.party.data.PlaceObject;
+
+/**
+ * This interface provides a convenient means for decoupling user
+ * interface components that interact with a place object and that need to
+ * keep themselves up to date when the client moves from place to place.
+ *
+ * <p> 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.
+ *
+ * <p> 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 <code>PlaceView</code> 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 <code>PlaceView</code>.
+ *
+ * <p> 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);
+}