Tag: Unmounting

Handling Mounting And Unmounting Of Navigation Routes In React Native

In this article, we are going to walk through mounting and unmounting of navigation routes in React Native. An expected behavior of your app is that once the authentication condition is met, a new set of navigation routes are available only to logged-in users, while the other screens which were displayed before authentication is removed and can’t be returned to unless the user signs out of the application.

For security in your app, protected routes provide you with a way to only display certain information/content on your app to specific users, while restricting access from unauthorized persons.

We will be working with Expo for this project because it’ll help us focus on the problem at hand instead of worrying about a lot of setups. The exact same steps in this article could be followed for a bare React Native application.

You need some familiarity with JavaScript and React Native to follow through with this tutorial. Here are a few important things you should already be familiar with:

• Custom components in React Native (how to create components, receive, pass, and use props in a component). Read more.
• React Navigation. Read more.
• Stack Navigator in React Native. Read more.
• Basic Knowledge of React Native Core components (<View/>, <Text/>, etc.). Read more.
• React Native AsyncStorage. Read more.
• Context API. Read more.

Project Setup And Base Authentication

If you’re new to using expo and don’t know how to install expo, visit the official documentation. Once the installation is complete, go ahead to initialize a new React Native project with expo from our command prompt:

expo init navigation-project

You will be presented with some options to choose how you want the base setup to be:

In our case, let’s select the first option to set up our project as a blank document. Now, wait until the installation of the JavaScript dependencies is complete.

Once our app is set up, we can change our directory to our new project directory and open it in your favorite code editor. We need to install the library we will be using for AsyncStorage and our navigation libraries. Inside your folder directory in your terminal, paste the command above and choose a template (blank would work) to install our project dependencies.

Let’s look at what each of these dependencies is for:

• @react-native-community/async-storage
  Like localStorage on the web, it is a React Native API for persisting data on a device in key-value pairs.
• @react-native-community/masked-view, react-native-screens, react-native-gesture-handle
  These dependencies are core utilities that are used by most navigators to create the navigation structure in the app. (Read more in Getting started with React Native navigation.)
• @react-navigation/native
  This is the dependency for React Native navigation.
• @react-navigation/stack
  This is the dependency for stack navigation in React Native.

npm install @react-native-community/async-storage @react-native-community/masked-view @react-navigation/native @react-navigation/stack react-native-screens react-native-gesture-handle

To start the application use expo start from the app directory in your terminal. Once the app is started, you can use the expo app from your mobile phone to scan the bar code and view the application, or if you have an android emulator/IOS simulator, you can open the app through them from the expo developer tool that opens up in your browser when you start an expo application. For the images examples in this article, we will be using Genymotions to see our result. Here’s what our final result will look like in Genymotions:

Folder Structures

Let us create our folder structure from the start so that it’s easier for us to work with it as we proceed:

We need two folders first:

• context
  This folder will hold the context for our entire application as we will be working with Context API for global state management.
• views
  This folder will hold both the navigation folder and the views for different screens.

Go ahead and create the two folders in your project directory.

Inside the context folder, create a folder called authContext and create two file inside of the authContext folder:

• AuthContext.js,
• AuthState.js.

We will need these files when we start working with Context API.

Now go to the views folder we created and create two more folders inside of it, namely:

• navigation,
• screens.

Now, we are not yet finished, inside the screens folder, create these two more folders:

• postAuthScreens,
• preAuthScreens.

If you followed the folder setup correctly, this is how your folder structure should look like at the moment:

Creating Our First Screen

Now let’s create our first screen and call it the welcomeScreen.js inside the preAuthScreens folder.

preAuthScreens > welcomeScreen.js

Here’s the content of our welcomeScreen.js file:

import React from 'react'; import { View, Text, Button, StyleSheet, TextInput } from 'react-native';  const WelcomeScreen = () => {    const onUserAuthentication = () => {     console.log("User authentication button clicked")   }    return (     <View style={styles.container}>       <Text style={styles.header}>Welcome to our App!</Text>       <View>         <TextInput style={styles.inputs} placeholder="Enter your email here.." />         <TextInput style={styles.inputs} secureTextEntry={true} placeholder="Enter your password here.." /> <Button  title="AUTHENTICATE" onPress={onUserAuthentication} />       </View>     </View>   ) }  const styles = StyleSheet.create({   container: {     flex: 1,     backgroundColor: '#fff',     alignItems: 'center',     justifyContent: 'center',   },   header: {     fontSize: 25,     fontWeight: 'bold',     marginBottom: 30   },   inputs: {     width: 300,     height: 40,     marginBottom: 10,     borderWidth: 1,   } })  export default WelcomeScreen 

Here’s what we did in the code block above:

First, we imported the things we need from the React Native library, namely, View, Text, Button, TextInput. Next, we created our functional component WelcomeScreen.

You’ll notice that we imported the StyleSheet from React Native and used it to define styles for our header and also our <TextInput />.

Lastly, we export the WelcomeScreen component at the bottom of the code.

Now that we are done with this, let’s get this component to function as expected by using the useState hook to store the values of the inputs and update their states anytime a change happens in the input fields. We will also bring import the useCallback hook from React as we will be needing it later to hold a function.

First, while we are still in the WelcomeScreen component, we need to import the useState and useCallback from React.

import React, { useState, useCallback } from 'react';

Now inside the WelcomeScreen functional component, let’s create the two states for the email and password respectively:

... const WelcomeScreen = () => {   const [email, setEmail] = useState('')   const [password, setPassword] = useState('')   return (     ...   ) } ...

Next, we need to modify our <TextInput /> fields so that the get their value from their respective states and update their state when the value of the input is updated:

import React, { useState, useCallback } from 'react'; import { View, Text, Button, StyleSheet, TextInput } from 'react-native';  const WelcomeScreen = () => {   const [email, setEmail] = useState('')   const [password, setPassword] = useState('')    const onInputChange = (value, setState) => {     setState(value);   }   return (     <View>       ...
      <View>         <TextInput           style={styles.inputs}           placeholder="Enter your email here.."           value={email}           onChangeText={(value) => onInputChange(value, setEmail)}         />         <TextInput           style={styles.inputs}           secureTextEntry={true}           placeholder="Enter your password here.."           value={password}           onChangeText={(value) => onInputChange(value, setPassword)}         />         ...       </View>     </View>   ) } ... 

In the code above, here is what we did:

• We made the value of each of the text inputs to point to their respective states.
• We added the onChangeText handler to our text inputs. This fires up anytime a new value is entered or deleted from the input fields.
• We called our onInputChange function which accepts two arguments:
  • The current value is supplied by the onChangeText handler.
  • The setter of the state that should be updated (for the first input field we pass setEmail and the second we pass setPassword.
  • Finally, we write our onInputChange function, and our function does only one thing: It updates the respective states with the new value.

The next thing we need to work on is the onUserAuthentication() function with is called whenever the button for the form submission is clicked.

Ideally, the user must have already created an account and login will involve some backend logic of some sort to check that the user exists and then assign a token to the user. In our case, since we are not using any backend, we will create an object holding the correct user login detail, and then only authenticate a user when the values they enter matches our fixed values from the login object of email and password that we will create.

Here’s the code we need to do this:

...  const correctAuthenticationDetails = {   email: 'demouser@gmail.com',   password: 'password' } const WelcomeScreen = () => {   ...    // This function gets called when the AUTHENTICATE button is clicked   const onUserAuthentication = () => {     if (       email !== correctAuthenticationDetails.email ||       password !== correctAuthenticationDetails.password     ) {       alert('The email or password is incorrect')       return     }       // In here, we will handle what happens if the login details are       // correct   }    ...   return (     ...   ) } ... 

One of the first things you’ll notice in the code above is that we defined a correctAuthenticationDetails (which is an object that holds the correct login details we expect a user to supply) outside of the WelcomeScreen() functional component.

Next, we wrote the content of the onUserAuthentication() function and used a conditional statement to check if the email or password held in the respective states does not match the one we supplied in our object.

If you would like to see what we have done so far, import the WelcomeScreen component into your App.js like this:

Open the App.js file and put this replace the entire code with this:

import { StatusBar } from 'expo-status-bar'; import React from 'react'; import { View } from 'react-native'; import WelcomeScreen from './views/screens/preAuthScreens/welcomeScreen'; export default function App() {   return (     <View>       <StatusBar style="auto" />       <WelcomeScreen />     </View>   ); } 

Looking closely at the code above, you’ll see that what we did was import the WelcomeScreen component and then used it in the App() function.

Here’s what the result looks like of our WelcomeScreen looks like:

Now that we are done building the WelcomeScreen component, let’s move ahead and start working with Context API for managing our global state.

Why Context API?

Using Context API, we do not need to install any additional library into ReactJS, it is less stressful to set up, and is one of the most popular ways of handling global state in ReactJS. For lightweight state management, it is a good choice.

Creating Our Context

If you recall, we created a context folder earlier and created a subfolder inside of it called the authContext.

Now let’s navigate to the AuthContext.js file in the authContext folder and create our context:

context > authContext > AuthContext.js

 import React, { createContext } from 'react'; const AuthContext = createContext(); export default AuthContext; 

The AuthContext we just created holds the loading state value and the userToken state values. Currently, in the createContext we declared in the code-block above, we didn’t initialize any default values here so our context is currently undefined. An example value of the auth context could be {loading: false, userToken: 'abcd}

The AuthState.js file holds our Context API logic and their state values. Functions written here can be called from anywhere in our app and when they update values in state, it is updated globally also.

First, let’s bring in all the imports we will need in this file:

context > AuthContext > AuthState.js

import React, { useState } from 'react'; import AuthContext from './AuthContext'; import AsyncStorage from '@react-native-community/async-storage';

We imported the useState() hook from ReactJS to hold our states, we imported the AuthContext file we created above because this is where our empty context for authentication is initialized and we will need to use it as you’ll see later on while we progress, finally we import the AsyncStorage package (similar to localStorage for the web).

AsyncStorage is a React Native API that allows you to persist data offline over the device in a React Native application.

...  const AuthState = (props) => {     const [userToken, setUserToken] = useState(null);     const [isLoading, setIsLoading] = useState(true);      const onAuthentication = async() => {         const USER_TOKEN = "drix1123q2"         await AsyncStorage.setItem('user-token', USER_TOKEN);         setUserToken(USER_TOKEN);         console.warn("user has been authenticated!")     }      return (         <AuthContext.Provider             value={{                 onAuthentication,             }}         >             {props.children}         </AuthContext.Provider>     ) } export default AuthState; 

In the code block above here’s what we did:

• We declared two states for the userToken and isLoading. The userToken state will be used to store the token saved to AsyncStorage, while the isLoading state will be used to track the loading status (initially it is set to true). We will find out more about the use of these two states as we proceed.

• Next, we wrote our onAuthentication() function. This function is an async function that gets called when the login button is clicked from the welcomeScreen.jsx file. This function will only get called if the email and password the user has supplied matches the correct user detail object we provided. Usually what happens during authentication is that a token is generated for the user after the user is authenticated on the backend using a package like JWT, and this token is sent to the frontend. Since we are not going into all of that for this tutorial, we created a static token and kept it in a variable called USER_TOKEN.

• Next, we use the await keyword to set our user token to AsyncStorage with the name user-token. The console.warn() statement is just used to check that everything went right, you can take it off whenever you like.

• Finally, we pass our onAuthenticated function as a value inside our <AuthContext.Provider> so that we can access and call the function from anywhere in our app.

screens > preAuth > welcomeScreen.js

First, import useContext from ReactJS and import the AuthContext from the AuthContext.js file.

import React, { useState, useContext } from 'react'; import AuthContext from '../../../context/authContext/AuthContext' ...

Now, inside the welcomeScreen() functional component, let’s use the context which we have created:

... const WelcomeScreen = () => {   const { onAuthentication } = useContext(AuthContext)   const onUserAuthentication = () => {     if (       email !== correctAuthenticationDetails.email ||       password !== correctAuthenticationDetails.password     ) {       alert('The email or password is incorrect')       return     }     onAuthentication()   }   return (     ...   ) } ... 

In the above code block, we destructured the onAuthentication function from our AuthContext and then we called it inside our onUserAuthentication() function and removed the console.log() statement which was there before now.

Right now, this will throw an error because we don’t yet have access to the AuthContext. To use the AuthContext anywhere in your application, we need to wrap the top-level file in our app with the AuthState (in our case, it is the App.js file).

Go to the App.js file and replace the code there with this:

import React from 'react'; import WelcomeScreen from './views/screens/preAuthScreens/welcomeScreen'; import AuthState from './context/authContext/AuthState'  export default function App() {   return (     <AuthState>       <WelcomeScreen />     </AuthState>   ); } 

We’ve come so far and we’re done with this section. Before we move into the next section where we set up our routing, let’s create a new screen. The screen we are about to create will be the HomeScreen.js file which is supposed to show up only after successful authentication.

Go to: screens > postAuth.

Create a new file called HomeScreen.js. Here’s the code for the HomeScreen.js file:

screens > postAuth > HomeScreen.js

import React from 'react'; import { View, Text, Button, StyleSheet } from 'react-native';  const HomeScreen = () => {    const onLogout = () => {     console.warn("Logout button cliked")   }    return (     <View style={styles.container}>       <Text>Now you're authenticated! Welcome!</Text>       <Button title="LOG OUT" onPress={onLogout} />     </View>   ) }  const styles = StyleSheet.create({   container: {     flex: 1,     backgroundColor: '#fff',     alignItems: 'center',     justifyContent: 'center',   }, })  export default HomeScreen 

For now, the logout button has a dummy console.log() statement. Later on, we will create the logout functionality and pass it to the screen from our context.

Setting Up Our Routes

We need to create three (3) files inside our navigation folder:

• postAuthNavigator.js,
• preAuthNavigator.js,
• AppNavigator.js.

Once you’ve created these three files, navigate to the preAuthNaviagtor.js file you just created and write this:

navigation > preAuthNavigator.js

import React from "react"; import { createStackNavigator } from "@react-navigation/stack"; import WelcomeScreen from "../screens/preAuthScreens/welcomeScreen";  const PreAuthNavigator = () => {     const { Navigator, Screen } = createStackNavigator();      return (         <Navigator initialRouteName="Welcome">             <Screen                 name="Welcome"                 component={WelcomeScreen}             />         </Navigator>     ) } export default PreAuthNavigator; 

In the file above, here’s what we did:

• We imported the createStackNavigator from the @react-navigation/stack which we are using for our stack navigation. The createStackNavigatorProvides a way for your app to transition between screens where each new screen is placed on top of a stack. By default the stack navigator is configured to have the familiar iOS and Android look & feel: new screens slide in from the right on iOS, fade in from the bottom on Android. Click here if you want to learn more about the stack navigator in React Native.
• We destructured Navigator and Screen from the createStackNavigator().
• In our return statement, we created our navigation with the <Navigator/> and created our screen with the <Screen/>. this means that if we had multiple screens that can be accessed before authentication, we will have multiple <Screen/> tags here representing them.
• Finally, we export our PreAuthNavigator component.

Let us do a similar thing for the postAuthNavigator.js file.

navigation > postAuthNavigator.js

import React from "react"; import { createStackNavigator } from "@react-navigation/stack"; import HomeScreen from "../screens/postAuthScreens/HomeScreen"; const PostAuthNavigator = () => {   const { Navigator, Screen} = createStackNavigator();   return (     <Navigator initialRouteName="Home">       <Screen         name="Home"         component={HomeScreen}       />     </Navigator>    ) } export default PostAuthNavigator; 

As we see in the code above, the only difference between the preAuthNavigator.js and the postAuthNavigator.js is the screen being rendered. While the first one takes the WelcomeScreen, the postAuthNavigator.js takes the HomeScreen.

To create our AppNavigator.js we need to create a few things.

Since the AppNavigator.js is where we will be switching and checking which route will be available for access by the user, we need several screens in place for this to work properly, let’s outline the things we need to create first:

1. TransitionScreen.js
   While the app decides which navigation it is going to mount, we want a transition screen to show up. Typically, the transition screen will be a loading spinner or any other custom animation chosen for the app, but in our case, we will use a basic <Text/> tag to display loading….
2. checkAuthenticationStatus()
   This function is what we will be calling to check the authentication status which will determine which navigation stack is going to be mounted. We will create this function in our context and use it in the Appnavigator.js.

Now, let’s go ahead and create our TransitionScreen.js file.

screens > TransitionScreen.js

import React from 'react'; import { Text, View } from 'react-native';  const TransitionScreen = () => {   return (     <View>       <Text>Loading...</Text>     </View>   ) }  export default TransitionScreen 

Our transition screen is just a simple screen that shows loading text. We will see where to use this as we proceed in this article.

Next, let us go to our AuthState.js and write our checkAuthenticationStatus():

context > authContext > AuthState.js

import React, { useState, useEffect } from 'react'; import AuthContext from './AuthContext'; import AsyncStorage from '@react-native-community/async-storage';  const AuthState = (props) => {     const [userToken, setUserToken] = useState(null);     const [isLoading, setIsLoading] = useState(true);      ...     useEffect(() => {         checkAuthenticationStatus()     }, [])      const checkAuthenticationStatus = async () => {         try {             const returnedToken = await AsyncStorage.getItem('user-toke             n');             setUserToken(returnedToken);             console.warn('User token set to the state value)         } catch(err){             console.warn(Here's the error that occured while retrievin             g token: $ {err})          }         setIsLoading(false)     }       const onAuthentication = async() => {         ...     }      return (         <AuthContext.Provider             value={{                 onAuthentication,                 userToken,                 isLoading,             }}         >             {props.children}         </AuthContext.Provider>     ) } export default AuthState; 

In the code block above, we wrote the function checkAuthenticationStatus(). In our function, here’s what we are doing:

• We used the await keyword to get our token from AsyncStorage. With AsyncStorage, if there’s no token supplied, it returns null. Our initial userToken state is set to null also.
• We use the setUserToken to set our returned value from AsyncStorage as our new userToken. If the returned value is null, it means our userToken remains null.
• After the try{}…catch(){} block, we set isLoading to false because the function to check authentication status is complete. We’ll need the value of isLoading to know if we should still be displaying the TransitionScreen or not. It’s worth considering setting an error if there is an error retrieving the token so that we can show the user a “Retry” or “Try Again” button when the error is encountered.
• Whenever AuthState mounts we want to check the authentication status, so we use the useEffect() ReactJS hook to do this. We call our checkAuthenticationStatus() function inside the useEffect() hook and set the value of isLoading to false when it is done.
• Finally, we add our states to our <AuthContext.Provider/> values so that we can access them from anywhere in our app covered by the Context API.

Now that we have our function, it is time to go back to our AppNavigator.js and write the code for mounting a particular stack navigator based on the authentication status:

navigation > AppNavigator.js

First, we will import all we need for our AppNavigator.js.

import React, { useEffect, useContext } from "react"; import PreAuthNavigator from "./preAuthNavigator"; import PostAuthNavigator from "./postAuthNavigator"; import { NavigationContainer } from "@react-navigation/native" import { createStackNavigator } from "@react-navigation/stack"; import AuthContext from "../../context/authContext/AuthContext"; import TransitionScreen from "../screens/TransitionScreen"; 

Now that we have all our imports, let’s create the AppNavigator() function.

... const AppNavigator = () => {  }  export default AppNavigator 

Next, we will now go ahead to write the content of our AppNavigator() function:

import React, { useState, useEffect, useContext } from "react"; import PreAuthNavigator from "./preAuthNavigator"; import PostAuthNavigator from "./postAuthNavigator"; import { NavigationContainer } from "@react-navigation/native" import { createStackNavigator } from "@react-navigation/stack"; import AuthContext from "../../context/authContext/AuthContext"; import TransitionScreen from "../screens/transition";  const AppNavigator = () => {     const { Navigator, Screen } = createStackNavigator();     const authContext = useContext(AuthContext);     const { userToken, isLoading } = authContext;     if(isLoading) {       return <TransitionScreen />     }     return (     <NavigationContainer>       <Navigator>         {            userToken == null ? (             <Screen               name="PreAuth"               component={PreAuthNavigator}               options={{ header: () => null }}             />           ) : (             <Screen                name="PostAuth"               component={PostAuthNavigator}               options={{ header: () => null }}             />           )         }       </Navigator>     </NavigationContainer>   ) }  export default AppNavigator 

In the above block of code, here’s an outline of what we did:

• We created a stack navigator and destructured the Navigator and Screen from it.
• We imported the userToken and the isLoading from our AuthContext
• When the AuthState mounts, the checkAuthenticationStatus() is called in the useEffecct hook there. We use the if statement to check if isLoading is true, if it is true the screen we return is our <TransitionScreen /> which we created earlier because the checkAuthenticationStatus() function is not yet complete.
• Once our checkAuthenticationStatus() is complete, isLoading is set to false and we return our main Navigation components.
• The NavigationContainer was imported from the @react-navigation/native. It is only used once in the main top-level navigator. Notice that we are not using this in the preAuthNavigator.js or the postAuthNavigator.js.
• In our AppNavigator(), we still create a stack navigator. If the userToken gotten from our Context API is null, we mount the PreAuthNavigator, if its value is something else (meaning that the AsyncStorage.getItem() in the checkAuthenticationStatus() returned an actual value), then we mount the PostAuthNavigator. Our conditional rendering is done using the ternary operator.

Now we’ve set up our AppNavigator.js. Next, we need to pass our AppNavigator into our App.js file.

Let’s pass our AppNavigator into the App.js file:

App.js

 ... import AppNavigator from './views/navigation/AppNavigator';  ... return (     <AuthState>       <AppNavigator />     </AuthState>   ); 

Let’s now see what our app looks like at the moment:

Here’s what happens when you supply an incorrect credential while trying to log in:

Adding The Logout Functionality

At this point, our authentication and route selection process is complete. The only thing left for our app is to add the logout functionality.

The logout button is in the HomeScreen.js file. We passed an onLogout() function to the onPress attribute of the button. For now, we have a simple console.log() statement in our function, but in a little while that will change.

Now, let’s go to our AuthState.js and write the function for logout. This function simply clears the AsyncStorage where the user token is saved.

context > authContext > AuthState.js

... const AuthState = (props) => {     ...      const userSignout = async() => {         await AsyncStorage.removeItem('user-token');         setUserToken(null);     }       return (       ...     ) }  export default AuthState; 

The userSignout() is an asynchronous function that removes the user-token from our AsyncStorage.

Now we need to call the userSignout() function in our HomeScreen.js any time the logout button is clicked on.

Let’s go to our HomeScreen.js and use ther userSignout() from our AuthContext.

screens > postAuthScreens > HomeScreen.js

import React, { useContext } from 'react'; import { View, Text, Button, StyleSheet } from 'react-native'; import AuthContext from '../../../context/authContext/AuthContext'  const HomeScreen = () => {   const { userSignout } = useContext(AuthContext)    const onLogout = () => {     userSignout()   }   return (     <View style={styles.container}>       <Text>Now you're authenticated! Welcome!</Text>  <Button title="LOG OUT" onPress={onLogout} />     </View>   ) } ... 

In the above code block we imported thee useContext hook from ReactJS, then we imported our AuthContext. Next, we destructured the userSignout function from our AuthContext and this userSignout() function is called in our onLogout() function.

Now whenever our logout button is clicked, the user token in our AsyncStorage is cleared.

Voila! our entire process is finished.

Here’s what happens when you press the back button after you’re logged in:

Here’s what happens when you press the back button after logging out:

Here are some different behaviors we notice when using this pattern in our navigation stack switching:

1. You’ll notice that there was nowhere we needed to make use of navigation.navigate() or navigation.push() to go to another route after login. Once our state is updated with the user token, the navigation stack rendered is automatically changed.
2. Pressing the back button on your device after login is successful cannot take you back to the login page, instead, it closes the app entirely. This behavior is important because you don’t want the user to be able to return back to the login page except they log out of the app. The same thing applies to logging out — once the user logs out, they cannot use the back button to return to the HomeScreen screen, but instead, the app closes.

Conclusion

In many Apps, authentication is one of the most important parts because it confirms that the person trying to gain access to protected content has the right to access the information. Learning how to do it right is an important step in building a great, intuitive, and easy to use/navigate the application.

Building on top of this code, here are a few things you might consider adding:

• Form validation for validating input fields. Check out React Native form validation with Formik and Yup.
• Firebase authentication for integrating authentication with Gmail, Github, Facebook, Twitter, or your custom interface. Check out React Native Firebase.
• Code concepts for designers: Authentication and Authorization.

Here are also some important resources I found that will enlighten you more about authentication, security and how to do it right:

Resources

• React Native: User Authentication Flow Explained
• 10 React Security Best Practices
• Authentication Methods That Can Prevent The Next Breach
• View a live build/preview of our application here;
• View the project on GitHub.

Articles on Smashing Magazine — For Web Designers And Developers