Add back button functionality on Android

app/actions/actionTypes.js

 export const LOGIN = 'LOGIN';
 export const NAVIGATE = 'NAVIGATE';
+export const BACK = 'BACK';

app/actions/navigation.js

@@ -6,3 +6,9 @@ export function navigate(scene) {
     scene,
   };
 }
+
+export function back() {
+  return {
+    type: types.BACK,
+  };
+}

app/app.js

 import React from 'react';
+import { BackAndroid } from 'react-native';
 import { createStore, applyMiddleware, combineReducers } from 'redux';
 import { Provider } from 'react-redux';
 import thunk from 'redux-thunk';
 
 import * as reducers from './reducers';
 import ReduxNavigator from './components/navigator';
+import { back } from './actions/navigation';
 
 const createStoreWithMiddleware = applyMiddleware(thunk)(createStore);
 const reducer = combineReducers(reducers);
 const store = createStoreWithMiddleware(reducer);
 
+BackAndroid.addEventListener('hardwareBackPress', () => {
+  if (store.getState().navigation.previousScenes.length === 0) {
+    return false;
+  }
+  store.dispatch(back());
+  return true;
+});
+
 const Main = () =>
   <Provider store={store}>
     <ReduxNavigator />

app/components/navigator.js

@@ -14,7 +14,6 @@ const mapDispatchToProps = dispatch => ({
   navigate: scene => dispatch(actions.navigate(scene)),
 });
 
-
 const ReduxNavigator = (props) => {
   const currentScene = props.currentScene;
   switch (currentScene) {
@@ -31,5 +30,4 @@ ReduxNavigator.propTypes = {
   currentScene: React.PropTypes.string.isRequired,
 };
 
-
 export default connect(mapStateToProps, mapDispatchToProps)(ReduxNavigator);

app/reducers/navigation.js

 import * as types from '../actions/actionTypes';
 
 const initialState = {
+  previousScenes: [],
   currentScene: 'login',
 };
 
 
 export default function navigate(state = initialState, action = {}) {
+  const { currentScene, previousScenes } = state;
   switch (action.type) {
     case types.LOGIN:
       if (action.success) {
-        return { ...state, currentScene: 'welcome' };
+        return {
+          previousScenes: [
+            ...previousScenes,
+            currentScene,
+          ],
+          currentScene: 'welcome',
+        };
       }
       return { ...state };
+    case types.BACK: {
+      const scene = previousScenes.pop();
+      return {
+        previousScenes,
+        currentScene: scene,
+      };
+    }
     default:
       return { ...state };
   }