Add show next / previous item.

spec/app/pane-spec.coffee

@@ -17,10 +17,12 @@ describe "Pane", ->
       expect(pane.itemViews.find('#view-1')).toExist()
 
   describe ".showItem(item)", ->
-    it "hides all item views except the one being shown", ->
+    it "hides all item views except the one being shown and sets the currentItem", ->
+      expect(pane.currentItem).toBe view1
       pane.showItem(view2)
       expect(view1.css('display')).toBe 'none'
       expect(view2.css('display')).toBe ''
+      expect(pane.currentItem).toBe view2
 
     describe "when showing a model item", ->
       describe "when no view has yet been appended for that item", ->
@@ -42,3 +44,15 @@ describe "Pane", ->
         expect(pane.itemViews.find('#view-2')).not.toExist()
         pane.showItem(view2)
         expect(pane.itemViews.find('#view-2')).toExist()
+
+  describe "pane:show-next-item and pane:show-preview-item", ->
+    it "advances forward/backward through the pane's items, looping around at either end", ->
+      expect(pane.currentItem).toBe view1
+      pane.trigger 'pane:show-previous-item'
+      expect(pane.currentItem).toBe editSession2
+      pane.trigger 'pane:show-previous-item'
+      expect(pane.currentItem).toBe view2
+      pane.trigger 'pane:show-next-item'
+      expect(pane.currentItem).toBe editSession2
+      pane.trigger 'pane:show-next-item'
+      expect(pane.currentItem).toBe view1

src/app/pane.coffee

@@ -12,15 +12,42 @@ class Pane extends View
   @deserialize: ({wrappedView}) ->
     new Pane(deserialize(wrappedView))
 
+  currentItem: null
+  items: null
+
   initialize: (@items...) ->
     @viewsByClassName = {}
     @showItem(@items[0])
 
+    @command 'pane:show-next-item', @showNextItem
+    @command 'pane:show-previous-item', @showPreviousItem
+
+  showNextItem: =>
+    index = @getCurrentItemIndex()
+    if index < @items.length - 1
+      @showItemAtIndex(index + 1)
+    else
+      @showItemAtIndex(0)
+
+  showPreviousItem: =>
+    index = @getCurrentItemIndex()
+    if index > 0
+      @showItemAtIndex(index - 1)
+    else
+      @showItemAtIndex(@items.length - 1)
+
+  getCurrentItemIndex: ->
+    @items.indexOf(@currentItem)
+
+  showItemAtIndex: (index) ->
+    @showItem(@items[index])
+
   showItem: (item) ->
     @itemViews.children().hide()
     view = @viewForItem(item)
     unless view.parent().is(@itemViews)
       @itemViews.append(view)
+    @currentItem = item
     view.show()
 
   viewForItem: (item) ->
@@ -34,7 +61,6 @@ class Pane extends View
       else
         @viewsByClassName[viewClass.name] = new viewClass(item)
 
-
   serialize: ->
     deserializer: "Pane"
     wrappedView: @wrappedView?.serialize()