NavigationExperimental: Avoid double push on double-tap in UIExplorer

Reviewed By: javache

Differential Revision: D3033918

fb-gh-sync-id: 9085db138754f1aa557f0190456529e5e71ac27b
shipit-source-id: 9085db138754f1aa557f0190456529e5e71ac27b

Examples/UIExplorer/UIExplorerNavigationReducer.js

@@ -36,8 +36,12 @@ export type UIExplorerNavigationState = {
 };
 
 const UIExplorerStackReducer = StackReducer({
-  getPushedReducerForAction: (action) => {
+  getPushedReducerForAction: (action, lastState) => {
     if (action.type === 'UIExplorerExampleAction' && UIExplorerList.Modules[action.openExample]) {
+      if (lastState.children.find(child => child.key === action.openExample)) {
+        // The example is already open, we should avoid pushing examples twice
+        return null;
+      }
       return (state) => state || {key: action.openExample};
     }
     return null;

Libraries/NavigationExperimental/Reducer/NavigationStackReducer.js

@@ -29,7 +29,7 @@ export type NavigationStackReducerAction = BackAction | {
 
 export type ReducerForStateHandler = (state: NavigationState) => NavigationReducer;
 
-export type PushedReducerForActionHandler = (action: any) => ?NavigationReducer;
+export type PushedReducerForActionHandler = (action: any, lastState: NavigationParentState) => ?NavigationReducer;
 
 export type StackReducerConfig = {
   /*
@@ -93,7 +93,7 @@ function NavigationStackReducer({initialState, getReducerForState, getPushedRedu
       };
     }
 
-    const subReducerToPush = getPushedReducerForAction(action);
+    const subReducerToPush = getPushedReducerForAction(action, lastParentState);
     if (subReducerToPush) {
       return NavigationStateUtils.push(
         lastParentState,