Handles some boilerplate functionality.

git-svn-id: svn+ssh://src.earth.threerings.net/nenya/trunk@239 ed5b42cb-e716-0410-a449-f6a68f950b19

src/as/com/threerings/flash/FrameSprite.as

@@ -0,0 +1,49 @@
+//
+// $Id$
+
+package com.threerings.flash {
+
+import flash.display.Sprite;
+
+import flash.events.Event;
+
+/**
+ * Convenience superclass to use for sprites that need to update every frame.
+ * (One must be very careful to remove all ENTER_FRAME listeners when not needed, as they
+ * will prevent an object from being garbage collected!)
+ */
+public class FrameSprite extends Sprite
+{
+    public function FrameSprite ()
+    {
+        addEventListener(Event.ADDED_TO_STAGE, handleAdded);
+        addEventListener(Event.REMOVED_FROM_STAGE, handleRemoved);
+    }
+
+    /**
+     * Called when we're added to the stage.
+     */
+    protected function handleAdded (... ignored) :void
+    {
+        addEventListener(Event.ENTER_FRAME, handleFrame);
+        handleFrame(); // update immediately
+    }
+
+    /**
+     * Called when we're added to the stage.
+     */
+    protected function handleRemoved (... ignored) :void
+    {
+        removeEventListener(Event.ENTER_FRAME, handleFrame);
+    }
+
+    /**
+     * Called to update our visual appearance prior to the flash player each frame.
+     */
+    protected function handleFrame (... ignored) :void
+    {
+        // nothing here. Override in yor subclass.
+    }
+}
+
+}