Add Pane::observeItems

spec/pane-spec.coffee

@@ -292,6 +292,19 @@ describe "Pane", ->
       expect(item3.isDestroyed()).toBe true
       expect(pane.getItems()).toEqual []
 
+  describe "::observeItems()", ->
+    it "invokes the observer with all current and future items", ->
+      pane = new Pane(items: [new Item, new Item])
+      [item1, item2] = pane.getItems()
+
+      observed = []
+      pane.observeItems (item) -> observed.push(item)
+
+      item3 = new Item
+      pane.addItem(item3)
+
+      expect(observed).toEqual [item1, item2, item3]
+
   describe "when an item emits a destroyed event", ->
     it "removes it from the list of items", ->
       pane = new Pane(items: [new Item("A"), new Item("B"), new Item("C")])

src/pane.coffee

@@ -134,6 +134,15 @@ class Pane extends Model
   onDidMoveItem: (callback) ->
     @emitter.on 'did-move-item', callback
 
+  # Public: Invoke the given callback with all current and future items.
+  #
+  # * `callback` {Function} to be called with current and future items.
+  #
+  # Returns a {Disposable} on which `.dispose()` can be called to unsubscribe.
+  observeItems: (callback) ->
+    callback(item) for item in @getItems()
+    @onDidAddItem ({item}) -> callback(item)
+
   # Public: Invoke the given callback when the value of {::getActiveItem}
   # changes.
   #