Use PaneContainerModel::$activePaneItem for 'active-item-changed' events

Yay behaviors

package.json

@@ -50,7 +50,7 @@
     "temp": "0.5.0",
     "text-buffer": "0.12.0",
     "underscore-plus": "0.6.1",
-    "theorist": "~0.10.0",
+    "theorist": "~0.11.0",
     "delegato": "~0.4.0",
     "mixto": "~0.4.0"
   },

src/pane-container-model.coffee

@@ -14,6 +14,9 @@ class PaneContainerModel extends Model
     focusContext: null
     activePane: null
 
+  @behavior 'activePaneItem', ->
+    @$activePane.flatMapLatest (activePane) -> activePane?.$activeItem
+
   constructor: ->
     super
 

src/pane-container.coffee

@@ -26,27 +26,13 @@ class PaneContainer extends View
       @model = new PaneContainerModel({root: params?.root?.model})
 
     @subscribe @model.$root, 'value', @onRootChanged
+    @subscribe @model.$activePaneItem.changes, 'value', @onActivePaneItemChanged
     @subscribe @model, 'surrendered-focus', @onSurrenderedFocus
 
-    @subscribe this, 'pane:attached', (event, pane) =>
-      @triggerActiveItemChange() if @getActivePane() is pane
-
-    @subscribe this, 'pane:removed', (event, pane) =>
-      @triggerActiveItemChange() unless @getActivePane()?
-
-    @subscribe this, 'pane:became-active', =>
-      @triggerActiveItemChange()
-
-    @subscribe this, 'pane:active-item-changed', (event, item) =>
-      @triggerActiveItemChange() if @getActivePaneItem() is item
-
   viewForModel: (model) ->
     viewClass = model.getViewClass()
     model._view ?= new viewClass(model)
 
-  triggerActiveItemChange: ->
-    @trigger 'pane-container:active-pane-item-changed', [@getActivePaneItem()]
-
   serializeParams: ->
     model: @model.serialize()
 
@@ -68,6 +54,9 @@ class PaneContainer extends View
       @append(view)
       view.makeActive?()
 
+  onActivePaneItemChanged: (activeItem) =>
+    @trigger 'pane-container:active-pane-item-changed', [activeItem]
+
   onSurrenderedFocus: =>
     atom?.workspaceView?.focus()