Removes events for filtering and instead use a special interface to perform the filtering, updates ctor for WeightAttribute to only accept positive numbers for public, internally it could be negative numbers, updates the filtering to always ensure that core handlers are at the beginning

src/Umbraco.Core/ObjectResolution/ApplicationEventsResolver.cs

@@ -7,7 +7,7 @@ using umbraco.interfaces;
 
 namespace Umbraco.Core.ObjectResolution
 {
-	/// <summary>
+    /// <summary>
 	/// A resolver to return all IApplicationEvents objects
 	/// </summary>
 	/// <remarks>
@@ -52,21 +52,47 @@ namespace Umbraco.Core.ObjectResolution
 	        {
 	            if (_orderedAndFiltered == null)
 	            {
-                    _orderedAndFiltered = GetSortedValues().ToList();
-
-                    //raise event so the collection can be modified
-                    OnCollectionResolved(new ApplicationEventsEventArgs(_orderedAndFiltered));
+                    _orderedAndFiltered = GetSortedValues().ToList();                    
+                    OnCollectionResolved(_orderedAndFiltered);
                 }
 	            return _orderedAndFiltered;
 	        }
 		}
-
-	    public event EventHandler<ApplicationEventsEventArgs> CollectionResolved;
-
-        private void OnCollectionResolved(ApplicationEventsEventArgs e)
+        
+        /// <summary>
+        /// Allow any filters to be applied to the event handler list
+        /// </summary>
+        /// <param name="handlers"></param>
+        /// <remarks>
+        /// This allows custom logic to execute in order to filter or re-order the event handlers prior to executing,
+        /// however this also ensures that any core handlers are executed first to ensure the stabiliy of Umbraco.
+        /// </remarks>
+        private void OnCollectionResolved(List<IApplicationEventHandler> handlers)
         {
-            var handler = CollectionResolved;
-            if (handler != null) handler(this, e);
+            foreach (var filter in handlers.OfType<IApplicationEventsFilter>().ToArray())
+            {
+                filter.Filter(handlers);
+            }
+
+            //find all of the core handlers and their weight, remove them from the main list
+            var coreItems = new List<Tuple<IApplicationEventHandler, int>>();
+            foreach (var handler in handlers.ToArray())
+            {
+                //Yuck, but not sure what else we can do 
+                if (
+                    handler.GetType().Assembly.FullName.StartsWith("Umbraco.", StringComparison.OrdinalIgnoreCase)
+                    || handler.GetType().Assembly.FullName.StartsWith("Concorde."))
+                {
+                    coreItems.Add(new Tuple<IApplicationEventHandler, int>(handler, GetObjectWeight(handler)));
+                    handlers.Remove(handler);
+                }
+            }
+
+            //re-add the core handlers to the beginning of the list ordered by their weight
+            foreach (var coreHandler in coreItems.OrderBy(x => x.Item2))
+            {
+                handlers.Insert(0, coreHandler.Item1);
+            }            
         }
 
         /// <summary>
@@ -166,10 +192,7 @@ namespace Umbraco.Core.ObjectResolution
             _legacyResolver.Dispose();
             ResetCollections();
             _orderedAndFiltered.Clear();
-	        _orderedAndFiltered = null;
-
-            //Clear event handlers
-	        CollectionResolved = null;
+	        _orderedAndFiltered = null;            
 	    }
     }
 }