[Navigator]: Add a getter to get the current route that is focused from the navigation context.

Libraries/CustomComponents/Navigator/Navigation/NavigationContext.js

@@ -23,25 +23,34 @@
  * ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  *
  * @providesModule NavigationContext
- * @flow
  */
 'use strict';
 
 var NavigationEventEmitter = require('NavigationEventEmitter');
-var emptyFunction = require('emptyFunction');
 
-type EventSubscription = {
-  remove: Function
-};
+var emptyFunction = require('emptyFunction');
+var invariant = require('invariant');
+
+import type * as NavigationEvent from 'NavigationEvent';
+import type * as EventSubscription from 'EventSubscription';
 
 /**
  * Class that contains the info and methods for app navigation.
  */
 class NavigationContext {
   _eventEmitter: ?NavigationEventEmitter;
+  _currentRoute: any;
 
   constructor() {
     this._eventEmitter = new NavigationEventEmitter(this);
+    this._currentRoute = null;
+    this.addListener('didfocus', this._onDidFocus, this);
+  }
+
+  // TODO: @flow does not like this getter. Will add @flow check back once
+  // getter/setter is supported.
+  get currentRoute(): any {
+    return this._currentRoute;
   }
 
   addListener(
@@ -64,13 +73,23 @@ class NavigationContext {
     }
   }
 
-  dispose() {
+  dispose(): void {
     var emitter = this._eventEmitter;
     if (emitter) {
+      // clean up everything.
       emitter.removeAllListeners();
       this._eventEmitter = null;
+      this._currentRoute = null;
     }
   }
+
+  _onDidFocus(event: NavigationEvent): void {
+    invariant(
+      event.data && event.data.hasOwnProperty('route'),
+      'didfocus event should provide route'
+    );
+    this._currentRoute = event.data.route;
+  }
 }
 
 module.exports = NavigationContext;

Libraries/CustomComponents/Navigator/Navigation/__tests__/NavigationContext-test.js

@@ -0,0 +1,51 @@
+/**
+ * Copyright (c) 2015, Facebook, Inc.  All rights reserved.
+ *
+ * Facebook, Inc. (“Facebook”) owns all right, title and interest, including
+ * all intellectual property and other proprietary rights, in and to the React
+ * Native CustomComponents software (the “Software”).  Subject to your
+ * compliance with these terms, you are hereby granted a non-exclusive,
+ * worldwide, royalty-free copyright license to (1) use and copy the Software;
+ * and (2) reproduce and distribute the Software as part of your own software
+ * (“Your Software”).  Facebook reserves all rights not expressly granted to
+ * you in this license agreement.
+ *
+ * THE SOFTWARE AND DOCUMENTATION, IF ANY, ARE PROVIDED "AS IS" AND ANY EXPRESS
+ * OR IMPLIED WARRANTIES (INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
+ * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE) ARE DISCLAIMED.
+ * IN NO EVENT SHALL FACEBOOK OR ITS AFFILIATES, OFFICERS, DIRECTORS OR
+ * EMPLOYEES BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
+ * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
+ * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS;
+ * OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
+ * WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR
+ * OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THE SOFTWARE, EVEN IF
+ * ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+'use strict';
+
+jest
+  .dontMock('EmitterSubscription')
+  .dontMock('EventEmitter')
+  .dontMock('EventSubscriptionVendor')
+  .dontMock('NavigationContext')
+  .dontMock('NavigationEvent')
+  .dontMock('NavigationEventEmitter')
+  .dontMock('invariant');
+
+var NavigationContext = require('NavigationContext');
+
+describe('NavigationContext', () => {
+  it('defaults `currentRoute` to null', () => {
+    var context = new NavigationContext();
+    expect(context.currentRoute).toEqual(null);
+  });
+
+  it('updates `currentRoute`', () => {
+    var context = new NavigationContext();
+    context.emit('didfocus', {route: {name: 'a'}});
+    expect(context.currentRoute.name).toEqual('a');
+  });
+});
+
+