4 files changed, 249 insertions, 0 deletions
diff --git a/app_expo/navigators/index.ts b/app_expo/navigators/index.ts
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+++ b/app_expo/navigators/index.ts
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+export * from './main-navigator'
+export * from './root-navigator'
+export * from './navigation-utilities'
+// export other navigators from here
diff --git a/app_expo/navigators/main-navigator.tsx b/app_expo/navigators/main-navigator.tsx
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+++ b/app_expo/navigators/main-navigator.tsx
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+/**
+ * This is the navigator you will modify to display the logged-in screens of your app.
+ * You can use RootNavigator to also display an auth flow or other user flows.
+ *
+ * You'll likely spend most of your time in this file.
+ */
+import React from 'react'
+import { createStackNavigator } from '@react-navigation/stack'
+import { WelcomeScreen, DemoScreen, DemoListScreen, GraphScreen } from '../screens'
+
+/**
+ * This type allows TypeScript to know what routes are defined in this navigator
+ * as well as what properties (if any) they might take when navigating to them.
+ *
+ * If no params are allowed, pass through `undefined`. Generally speaking, we
+ * recommend using your MobX-State-Tree store(s) to keep application state
+ * rather than passing state through navigation params.
+ *
+ * For more information, see this documentation:
+ *   https://reactnavigation.org/docs/params/
+ *   https://reactnavigation.org/docs/typescript#type-checking-the-navigator
+ */
+export type PrimaryParamList = {
+  welcome: undefined
+  demo: undefined
+  demoList: undefined
+  graph: undefined
+}
+
+// Documentation: https://reactnavigation.org/docs/stack-navigator/
+const Stack = createStackNavigator<PrimaryParamList>()
+
+export function MainNavigator() {
+  return (
+    <Stack.Navigator
+      screenOptions={{
+        cardStyle: { backgroundColor: 'transparent' },
+        headerShown: false,
+      }}
+    >
+      <Stack.Screen name="graph" component={GraphScreen} />
+    </Stack.Navigator>
+  )
+}
+
+/**
+      <Stack.Screen name="welcome" component={WelcomeScreen} />
+      <Stack.Screen name="demo" component={DemoScreen} />
+      <Stack.Screen name="demoList" component={DemoListScreen} />
+ * A list of routes from which we're allowed to leave the app when
+ * the user presses the back button on Android.
+ *
+ * Anything not on this list will be a standard `back` action in
+ * react-navigation.
+ *
+ * `canExit` is used in ./app/app.tsx in the `useBackButtonHandler` hook.
+ */
+const exitRoutes = ['welcome']
+export const canExit = (routeName: string) => exitRoutes.includes(routeName)
diff --git a/app_expo/navigators/navigation-utilities.tsx b/app_expo/navigators/navigation-utilities.tsx
new file mode 100644
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+++ b/app_expo/navigators/navigation-utilities.tsx
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+import React, { useState, useEffect, useRef } from 'react'
+import { BackHandler } from 'react-native'
+import { PartialState, NavigationState, NavigationContainerRef } from '@react-navigation/native'
+
+export const RootNavigation = {
+  navigate(name: string) {
+    name // eslint-disable-line no-unused-expressions
+  },
+  goBack() {}, // eslint-disable-line @typescript-eslint/no-empty-function
+  resetRoot(state?: PartialState<NavigationState> | NavigationState) {}, // eslint-disable-line @typescript-eslint/no-unused-vars, @typescript-eslint/no-empty-function
+  getRootState(): NavigationState {
+    return {} as any
+  },
+}
+
+export const setRootNavigation = (ref: React.RefObject<NavigationContainerRef>) => {
+  for (const method in RootNavigation) {
+    RootNavigation[method] = (...args: any) => {
+      if (ref.current) {
+        return ref.current[method](...args)
+      }
+    }
+  }
+}
+
+/**
+ * Gets the current screen from any navigation state.
+ */
+export function getActiveRouteName(state: NavigationState | PartialState<NavigationState>) {
+  const route = state.routes[state.index]
+
+  // Found the active route -- return the name
+  if (!route.state) return route.name
+
+  // Recursive call to deal with nested routers
+  return getActiveRouteName(route.state)
+}
+
+/**
+ * Hook that handles Android back button presses and forwards those on to
+ * the navigation or allows exiting the app.
+ */
+export function useBackButtonHandler(
+  ref: React.RefObject<NavigationContainerRef>,
+  canExit: (routeName: string) => boolean,
+) {
+  const canExitRef = useRef(canExit)
+
+  useEffect(() => {
+    canExitRef.current = canExit
+  }, [canExit])
+
+  useEffect(() => {
+    // We'll fire this when the back button is pressed on Android.
+    const onBackPress = () => {
+      const navigation = ref.current
+
+      if (navigation == null) {
+        return false
+      }
+
+      // grab the current route
+      const routeName = getActiveRouteName(navigation.getRootState())
+
+      // are we allowed to exit?
+      if (canExitRef.current(routeName)) {
+        // let the system know we've not handled this event
+        return false
+      }
+
+      // we can't exit, so let's turn this into a back action
+      if (navigation.canGoBack()) {
+        navigation.goBack()
+
+        return true
+      }
+
+      return false
+    }
+
+    // Subscribe when we come to life
+    BackHandler.addEventListener('hardwareBackPress', onBackPress)
+
+    // Unsubscribe when we're done
+    return () => BackHandler.removeEventListener('hardwareBackPress', onBackPress)
+  }, [ref])
+}
+
+/**
+ * Custom hook for persisting navigation state.
+ */
+export function useNavigationPersistence(storage: any, persistenceKey: string) {
+  const [initialNavigationState, setInitialNavigationState] = useState()
+  const [isRestoringNavigationState, setIsRestoringNavigationState] = useState(true)
+
+  const routeNameRef = useRef()
+  const onNavigationStateChange = (state) => {
+    const previousRouteName = routeNameRef.current
+    const currentRouteName = getActiveRouteName(state)
+
+    if (previousRouteName !== currentRouteName) {
+      // track screens.
+      __DEV__ && console.tron.log(currentRouteName)
+    }
+
+    // Save the current route name for later comparision
+    routeNameRef.current = currentRouteName
+
+    // Persist state to storage
+    storage.save(persistenceKey, state)
+  }
+
+  const restoreState = async () => {
+    try {
+      const state = await storage.load(persistenceKey)
+      if (state) setInitialNavigationState(state)
+    } finally {
+      setIsRestoringNavigationState(false)
+    }
+  }
+
+  useEffect(() => {
+    if (isRestoringNavigationState) restoreState()
+  }, [isRestoringNavigationState])
+
+  return { onNavigationStateChange, restoreState, initialNavigationState }
+}
diff --git a/app_expo/navigators/root-navigator.tsx b/app_expo/navigators/root-navigator.tsx
new file mode 100644
index 0000000..ed48dd5
--- /dev/null
+++ b/app_expo/navigators/root-navigator.tsx
@@ -0,0 +1,59 @@
+/**
+ * The root navigator is used to switch between major navigation flows of your app.
+ * Generally speaking, it will contain an auth flow (registration, login, forgot password)
+ * and a "main" flow (which is contained in your MainNavigator) which the user
+ * will use once logged in.
+ */
+import React from 'react'
+import { NavigationContainer, NavigationContainerRef } from '@react-navigation/native'
+import { createStackNavigator } from '@react-navigation/stack'
+import { MainNavigator } from './main-navigator'
+import { color } from '../theme'
+
+/**
+ * This type allows TypeScript to know what routes are defined in this navigator
+ * as well as what properties (if any) they might take when navigating to them.
+ *
+ * We recommend using MobX-State-Tree store(s) to handle state rather than navigation params.
+ *
+ * For more information, see this documentation:
+ *   https://reactnavigation.org/docs/params/
+ *   https://reactnavigation.org/docs/typescript#type-checking-the-navigator
+ */
+export type RootParamList = {
+  mainStack: undefined
+}
+
+const Stack = createStackNavigator<RootParamList>()
+
+const RootStack = () => {
+  return (
+    <Stack.Navigator
+      screenOptions={{
+        cardStyle: { backgroundColor: color.palette.deepPurple },
+        headerShown: false,
+      }}
+    >
+      <Stack.Screen
+        name="mainStack"
+        component={MainNavigator}
+        options={{
+          headerShown: false,
+        }}
+      />
+    </Stack.Navigator>
+  )
+}
+
+export const RootNavigator = React.forwardRef<
+  NavigationContainerRef,
+  Partial<React.ComponentProps<typeof NavigationContainer>>
+>((props, ref) => {
+  return (
+    <NavigationContainer {...props} ref={ref}>
+      <RootStack />
+    </NavigationContainer>
+  )
+})
+
+RootNavigator.displayName = 'RootNavigator'