use BackHandler instead of BackAndroid, fix expo#461

Closes expo#462

fbshipit-source-id: 4243d1f

README.md

@@ -361,7 +361,7 @@ on the left or right of the title.
 
    // ...
  }
- 
+
  @connect()
  class SignOutButton extends React.Component {
    render() {
@@ -421,7 +421,7 @@ will be rendered in the left position of the `navigationBar`.
 will be rendered in the title position of the `navigationBar`.
 - `renderRight` - a function that should return a React component that
 will be rendered in the right position of the `navigationBar`.
-- `renderBackground` - a function that should return a React component that 
+- `renderBackground` - a function that should return a React component that
 will be rendered in the background of the `navigationBar`.
 
 ## TabNavigation
@@ -734,12 +734,12 @@ export default screenTracking;
 
 ### Android back button handling
 
-React Native includes a global `BackAndroid` module. Rather than using this module 
-directly, include the `AndroidBackButtonBehavior` component in routes where you'd 
+React Native includes a global `BackHandler` module. Rather than using this module
+directly, include the `AndroidBackButtonBehavior` component in routes where you'd
 like to control the back button. `AndroidBackButtonBehavior` accepts
-`isFocused` and `onBackButtonPress`. If `isFocused` is true, the `onBackButtonPress` 
-will fire when the user presses the back button. You need to make sure that `onBackButtonPress` 
-returns a promise that wraps the function you want to be called. Eg. 
+`isFocused` and `onBackButtonPress`. If `isFocused` is true, the `onBackButtonPress`
+will fire when the user presses the back button. You need to make sure that `onBackButtonPress`
+returns a promise that wraps the function you want to be called. Eg.
 
 ```
 <AndroidBackButtonBehavior isFocused={someboolean}

src/ExNavigationBackButtonManager.js

@@ -2,12 +2,14 @@
  * @flow
  */
 
-import { BackAndroid } from 'react-native';
+import { BackAndroid, BackHandler } from 'react-native';
 
 import ExNavigationActions from './ExNavigationActions';
 
 import type { ExNavigationStore } from './ExNavigationStore';
 
+const Handler = BackHandler ? BackHandler : BackAndroid;
+
 /**
  * Manages a global listener, as well as any custom listeners, on the
  * Android hardware back button.
@@ -53,9 +55,9 @@ class ExNavigationBackButtonManager {
 
   disable() {
     this._listeners.forEach(listener =>
-      BackAndroid.removeEventListener('hardwareBackPress', listener)
+      Handler.removeEventListener('hardwareBackPress', listener)
     );
-    BackAndroid.addEventListener(
+    Handler.addEventListener(
       'hardwareBackPress',
       this._disabledBackButtonPress
     ); // Don't let app be exited.
@@ -68,11 +70,11 @@ class ExNavigationBackButtonManager {
   _setListeners(newListeners: Array<() => Promise<void>>) {
     this.disable();
     this._listeners = newListeners;
-    BackAndroid.removeEventListener(
+    Handler.removeEventListener(
       'hardwareBackPress',
       this._disabledBackButtonPress
     );
-    BackAndroid.addEventListener(
+    Handler.addEventListener(
       'hardwareBackPress',
       this._listeners[this._listeners.length - 1]
     );
@@ -84,7 +86,7 @@ class ExNavigationBackButtonManager {
     }
     const moreRoutes = await this._store.dispatch(ExNavigationActions.goBack());
     if (moreRoutes === false) {
-      BackAndroid.exitApp();
+      Handler.exitApp();
     }
   };