Handle widget hide/show logic

also only create a widget manager once

IPython/html/widgets/widget.js

@@ -19,9 +19,11
 // require(['components/underscore/underscore-min.js',
 //          'components/backbone/backbone-min.js'],
 
-var IPython = (function (IPython) {
     "use strict";
 
+// Only run once on a notebook.
+if (IPython.notebook.widget_manager == undefined) {
+
     //-----------------------------------------------------------------------
     // WidgetModel class
     //-----------------------------------------------------------------------
@@ -148,9 +150,24 var IPython = (function (IPython) {
         widget_view.render();
         widget_model.views.push(widget_view);
         
+        // Handle when the view element is remove from the page.
+        widget_view.$el.on("remove", function(){ 
+            var index = widget_model.views.indexOf(widget_view);
+            if (index > -1) {
+                widget_model.views.splice(index, 1);
+            }
+            widget_view.remove(); // Clean-up view 
+
+            // Close the comm if there are no views left.
+            if (widget_model.views.length()==0) {
+                widget_model.comm.close();     
+            }
+        });
+
         // Add the view's element to cell's widget div.
         widget_area
-            .append($("<div />").append(widget_view.$el));   
+            .append($("<div />").append(widget_view.$el))
+            .parent().show(); // Show the widget_area (parent of widget_subarea)
         
         // Update the view based on the model contents.
         widget_view.refresh();
@@ -235,7 +252,6 var IPython = (function (IPython) {
     IPython.WidgetModel = WidgetModel;
     IPython.WidgetView = WidgetView;
 
+    IPython.notebook.widget_manager = new WidgetManager(IPython.notebook.kernel.comm_manager);    
   
-    return IPython;
-
-}(IPython));
+}