Navigation Back support and examples for Android

Summary:
public
- Intro new back action
- Add support in the two main reducers
- Use it in examples to support Android back button
- Disable NavigationCard gestures on Android

Reviewed By: hedgerwang

Differential Revision: D2914154

fb-gh-sync-id: d4dce6538e19613a2ffca21e2e3b2ecaded3d5dc
shipit-source-id: d4dce6538e19613a2ffca21e2e3b2ecaded3d5dc

Libraries/NavigationExperimental/Reducer/NavigationFindReducer.js

@@ -22,7 +22,7 @@ import type {
   NavigationReducer
 } from 'NavigationState';
 
-function NavigationFindReducer(reducers: Array<NavigationReducer>): ?NavigationReducer {
+function NavigationFindReducer(reducers: Array<NavigationReducer>): NavigationReducer {
   return function(lastState: ?NavigationState, action: ?any): ?NavigationState {
     for (let i = 0; i < reducers.length; i++) {
       let reducer = reducers[i];

Libraries/NavigationExperimental/Reducer/NavigationStackReducer.js

@@ -18,7 +18,11 @@ import type {
   NavigationReducer,
 } from 'NavigationState';
 
-export type NavigationStackReducerAction = {
+import type {
+  BackAction,
+} from 'NavigationRootContainer';
+
+export type NavigationStackReducerAction = BackAction | {
   type: string,
 };
 
@@ -101,6 +105,7 @@ function NavigationStackReducer({initialStates, initialIndex, key, matchAction,
           action.state
         );
       case ActionTypes.POP:
+      case 'BackAction':
         if (lastParentState.index === 0 || lastParentState.children.length === 1) {
           return lastParentState;
         }

Libraries/NavigationExperimental/Reducer/NavigationTabsReducer.js

@@ -17,7 +17,8 @@ const NavigationStateUtils = require('NavigationState');
 import type {
   NavigationReducer,
   NavigationReducerWithDefault,
-  NavigationState
+  NavigationState,
+  NavigationParentState
 } from 'NavigationState';
 
 const ActionTypes = {
@@ -106,17 +107,15 @@ function NavigationTabsReducer({key, initialIndex, tabReducers}: TabsReducerConf
       }
     }
     const subReducers = tabReducers.map((tabReducer, tabIndex) => {
-      return function reduceTab(lastTabState: ?NavigationState, tabAction: ?any): ?NavigationState {
-        if (!lastTabState) {
-          return tabReducer(lastTabState, tabAction);
+      return function reduceTab(lastNavState: ?NavigationState, tabAction: ?any): ?NavigationState {
+        if (!tabReducer || !lastNavState) {
+          return lastNavState;
         }
-        if (!lastParentNavState) {
-          return lastTabState;
-        }
-        const lastSubTabState = lastParentNavState.children[tabIndex];
+        const lastParentNavState = NavigationStateUtils.getParent(lastNavState);
+        const lastSubTabState = lastParentNavState && lastParentNavState.children[tabIndex];
         const nextSubTabState = tabReducer(lastSubTabState, tabAction);
         if (nextSubTabState && lastSubTabState !== nextSubTabState) {
-          const tabs = lastParentNavState.children;
+          const tabs = lastParentNavState && lastParentNavState.children || [];
           tabs[tabIndex] = nextSubTabState;
           return {
             ...lastParentNavState,
@@ -129,11 +128,17 @@ function NavigationTabsReducer({key, initialIndex, tabReducers}: TabsReducerConf
     });
     let selectedTabReducer = subReducers.splice(lastParentNavState.index, 1)[0];
     subReducers.unshift(selectedTabReducer);
+    subReducers.push((lastParentNavState: ?NavigationState, action: ?any) => {
+      if (lastParentNavState && action && action.type === 'BackAction') {
+        return NavigationStateUtils.jumpToIndex(
+          lastParentNavState,
+          0
+        );
+      }
+      return lastParentNavState;
+    });
     const findReducer = NavigationFindReducer(subReducers);
-    if (findReducer) {
-      return findReducer(lastParentNavState, action);
-    }
-    return lastParentNavState;
+    return findReducer(lastParentNavState, action);
   };
 }