Add viewer.selectedEntityChanged event

CHANGES.md

@@ -26,6 +26,7 @@ Change Log
 * Add support for `Scene.pickPosition` in Columbus view and 2D. [#4990](https://github.com/AnalyticalGraphicsInc/cesium/pull/4990)
 * Added `Label.scaleByDistance` to control minimum/maximum label size based on distance from the camera. [#5019](https://github.com/AnalyticalGraphicsInc/cesium/pull/5019)
 * Add support for depth picking translucent primitives when `Scene.pickTranslucentDepth` is `true`. [#4979](https://github.com/AnalyticalGraphicsInc/cesium/pull/4979)
+* Added the event `Viewer.selectedEntityChanged`, which is raised when the value of `viewer.selectedEntity` changes.
 
 ### 1.30 - 2017-02-01
 

Source/Widgets/Viewer/Viewer.js

@@ -7,6 +7,7 @@ define([
         '../../Core/defineProperties',
         '../../Core/destroyObject',
         '../../Core/DeveloperError',
+        '../../Core/Event',
         '../../Core/EventHelper',
         '../../Core/isArray',
         '../../Core/Matrix4',
@@ -49,6 +50,7 @@ define([
         defineProperties,
         destroyObject,
         DeveloperError,
+        Event,
         EventHelper,
         isArray,
         Matrix4,
@@ -661,6 +663,7 @@ Either specify options.terrainProvider instead or set options.baseLayerPicker to
         this._zoomTarget = undefined;
         this._zoomPromise = undefined;
         this._zoomOptions = undefined;
+        this._selectedEntityChanged = new Event();
 
         knockout.track(this, ['_trackedEntity', '_selectedEntity', '_clockTrackedDataSource']);
 
@@ -1200,9 +1203,21 @@ Either specify options.terrainProvider instead or set options.baseLayerPicker to
                             selectionIndicatorViewModel.animateDepart();
                         }
                     }
+                    this._selectedEntityChanged.raiseEvent(value);
                 }
             }
         },
+        /**
+         * Gets the event that is raised when the selected entity chages
+         * @memberof Viewer.prototype
+         * @type {Event}
+         * @readonly
+         */
+        selectedEntityChanged : {
+            get : function() {
+                return this._selectedEntityChanged;
+            }
+        },
         /**
          * Gets or sets the data source to track with the viewer's clock.
          * @memberof Viewer.prototype

Specs/Widgets/Viewer/ViewerSpec.js

@@ -826,6 +826,30 @@ defineSuite([
         viewer.destroy();
     });
 
+    it('raises an event when the selected entity changes', function() {
+        var viewer = createViewer(container);
+
+        var dataSource = new MockDataSource();
+        viewer.dataSources.add(dataSource);
+
+        var entity = new Entity();
+        entity.position = new ConstantPositionProperty(new Cartesian3(123456, 123456, 123456));
+
+        dataSource.entities.add(entity);
+
+        var myEntity;
+        viewer.selectedEntityChanged.addEventListener(function(newSelection) {
+            myEntity = newSelection;
+        });
+        viewer.selectedEntity = entity;
+        expect(myEntity).toBe(entity);
+
+        viewer.selectedEntity = undefined;
+        expect(myEntity).toBeUndefined();
+
+        viewer.destroy();
+    });
+
     it('selectedEntity sets InfoBox properties', function() {
         var viewer = createViewer(container);