Resolved #199: TabView.selectedIndexChanged event.

ui/tab-view/tab-view.d.ts

@@ -4,6 +4,7 @@
 declare module "ui/tab-view" {
     import view = require("ui/core/view");
     import dependencyObservable = require("ui/core/dependency-observable");
+    import observable = require("data/observable");
 
     /**
      * Represents a tab view entry.
@@ -25,6 +26,21 @@ declare module "ui/tab-view" {
         iconSource?: string;
     }
 
+    /**
+     * Defines the data for the TabView.selectedIndexChanged event.
+     */
+    export interface SelectedIndexChangedEventData extends observable.EventData {
+        /**
+         * The old selected index.
+         */
+        oldIndex: number;
+        
+        /**
+         * The new selected index.
+         */
+        newIndex: number;
+    }
+
     /**
      * Represents a tab view.
      */
@@ -51,5 +67,23 @@ declare module "ui/tab-view" {
          * Gets the native iOS [UITabBarController](https://developer.apple.com/library/ios/documentation/UIKit/Reference/UITabBarController_Class/) that represents the user interface for this component. Valid only when running on iOS.
          */
         ios: UITabBarController;
+
+        /**
+         * String value used when hooking to the selectedIndexChanged event.
+         */
+        public static selectedIndexChangedEvent: string;
+        
+        /**
+         * A basic method signature to hook an event listener (shortcut alias to the addEventListener method).
+         * @param eventNames - String corresponding to events (e.g. "propertyChange"). Optionally could be used more events separated by `,` (e.g. "propertyChange", "change"). 
+         * @param callback - Callback function which will be executed when event is raised.
+         * @param thisArg - An optional parameter which will be used as `this` context for callback execution.
+         */
+        on(eventNames: string, callback: (data: observable.EventData) => void, thisArg?: any);
+
+        /**
+         * Raised when the selected index changes.
+         */
+        on(event: "selectedIndexChanged", callback: (args: SelectedIndexChangedEventData) => void, thisArg?: any);
     }
 }