Expo Router: Navigating Back & Passing Data (Screen A To B)

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Expo Router: Navigating Back & Passing Data (Screen A to B)

Hey guys! Let's dive into a common scenario in React Native with Expo Router: how to get data back from a previous screen after you've navigated away and then returned using router.back(). Imagine you're building an app and you've got Screen A and Screen B. You use router.push() to go from Screen A to Screen B, maybe to fill out a form or make a selection. Now, you want to send that data back to Screen A when you go back. Sound familiar? Let's break down how to do it efficiently.

Understanding the Problem: Data Flow with router.back()

So, the main issue is figuring out the best way to handle data transfer when you're moving backwards through your app's navigation stack. When you use router.push(), you're effectively adding a new screen to the stack. When you use router.back(), you're removing the current screen and going back to the one before it. By default, router.back() doesn't automatically pass any data. This means that if you just call router.back(), you'll simply be taken to the previous screen, but you won't have access to any data that was created or modified on the screen you're leaving.

This is where understanding state management and how Expo Router handles navigation comes into play. You have a few main options to pass data back and forth, each with its own advantages and disadvantages depending on the complexity of your app and the nature of the data you're passing. We'll explore these options in detail so you can choose the best approach for your specific needs. We will examine different strategies that can be used such as state management, params, and context. It's crucial to choose the method that best aligns with your project's architecture and the complexity of the data you're dealing with. Let's make sure you can confidently navigate and exchange data between your screens in your Expo Router app.

The Challenge of Retroactive Data

The real challenge lies in getting the data back to Screen A after Screen B has been displayed and then dismissed using router.back(). Screen B is the one generating the data, and Screen A is the one that needs it. This requires a mechanism to store or transmit the data. We'll be looking at methods that involve storing data in a place that both screens can access, or passing the data along with the navigation action. You need to keep in mind, we're not just pushing and popping screens; we're also aiming to synchronize data between them. The choice of strategy often depends on how long the data needs to persist, and how complex it is.

Let's get into the nitty-gritty of how to solve this data transfer problem!

Solution 1: Using router.push() with Params (Simple Data Transfer)

Alright, let's start with a straightforward method: passing data using router.push() and parameters. This is super handy when you only need to pass a small amount of data and don't require the data to persist across multiple navigation events. This approach is best for simple data transfers, such as passing a selected ID or a short string of text.

Here’s how it works. Instead of just calling router.push('/screenB'), you'll call something like router.push({pathname: '/screenB', params: { data: 'someData' }}). This is how you'll move to Screen B, and it's also how you'll include your data. The params object is where you bundle up the data you want to send.

On Screen B, you will access the data from the useLocalSearchParams() hook. This hook gives you access to the parameters passed to the screen. For example, if you send { data: 'someData' }, on Screen B, you'll be able to access the value with const { data } = useLocalSearchParams(). Now, when you call router.back() from Screen B, the data is not automatically available on Screen A. The key part of this method is that the data is already available on Screen B from the moment it is initialized.

Practical Implementation: Screen A to B

Here’s a basic example:

// Screen A
import { router } from 'expo-router';
import { useState } from 'react';
import { Button, TextInput, View } from 'react-native';

export default function ScreenA() {
  const [text, setText] = useState('');

  const goToScreenB = () => {
    router.push({
      pathname: '/screenB',
      params: { inputText: text },
    });
  };

  return (
    <View>
      <TextInput onChangeText={setText} value={text} placeholder="Enter text" />
      <Button title="Go to Screen B" onPress={goToScreenB} />
    </View>
  );
}

And now Screen B:

// Screen B
import { useLocalSearchParams, router } from 'expo-router';
import { Text, View, Button } from 'react-native';

export default function ScreenB() {
  const { inputText } = useLocalSearchParams();

  return (
    <View>
      <Text>You entered: {inputText}</Text>
      <Button title="Go Back" onPress={() => router.back()} />
    </View>
  );
}

As you can see, the inputText is passed from Screen A to Screen B using params. It is directly accessible to Screen B.

Advantages of using params:

  • Simple: Super easy to implement for passing basic data.
  • Direct Access: The data is readily available in the target screen.
  • Suitable for small data: Ideal when passing strings, numbers, or simple objects.

Disadvantages of using params:

  • Limited data: Doesn't handle complex data structures or large amounts of data well.
  • Persistence: Data only exists during the screen's lifespan. Won't persist if the app is closed or navigated away from and back to.

This method is great for quick, simple data transfers. But what if you need more robust solutions for handling larger, more complex data, or if you need to retain the data across multiple navigations?

Solution 2: State Management with Context or a Dedicated Library

Now, let's level up our game and look into using a state management solution. This is great when you need to share data across multiple screens, or if the data is complex and needs to be updated. This is one of the most powerful and flexible ways to manage data in your Expo Router app. Using this approach allows you to separate the data from the navigation, making your code easier to manage and scale.

For this approach, you can choose from various libraries like React Context, Redux, or MobX. I'll walk through a basic example with React Context since it's built into React and doesn't require any additional setup. The core idea is simple: You create a context that holds your data, and any component can access or modify this data. This allows you to update the data in one place and have it reflect across your app.

Setting up the Context

First, you will need to create a context file (e.g., AppContext.js). In this file, you define your context and provide the data and methods to update it:

// AppContext.js
import React, { createContext, useState, useContext } from 'react';

const AppContext = createContext();

export const useAppContext = () => {
  return useContext(AppContext);
};

export const AppContextProvider = ({ children }) => {
  const [dataFromB, setDataFromB] = useState(null);

  const updateDataFromB = (newData) => {
    setDataFromB(newData);
  };

  const value = {
    dataFromB,
    updateDataFromB,
  };

  return <AppContext.Provider value={value}>{children}</AppContext.Provider>;
};

In this example, AppContext will store the data coming from Screen B (dataFromB). The updateDataFromB function allows you to update the data from anywhere in the app.

Wrapping your app

Next, you have to wrap your app with the context provider. This will make your context available to every part of your app.

// app/_layout.js
import { AppContextProvider } from '../AppContext';

export default function RootLayout() {
  return (
    <AppContextProvider>
      {/* Your app content */}
    </AppContextProvider>
  );
}

Implementing in Screen A and Screen B

Now, let's see how this works in Screen A and Screen B.

// Screen A
import {  View, Text, Button } from 'react-native';
import {  useRouter } from 'expo-router';
import { useAppContext } from '../AppContext';

export default function ScreenA() {
  const router = useRouter();
  const { dataFromB } = useAppContext();

  return (
    <View>
      <Text>Data from B: {dataFromB ? dataFromB : 'None'}</Text>
      <Button title="Go to B" onPress={() => router.push('/screenB')} />
    </View>
  );
}

// Screen B
import {  View, Text, Button, TextInput } from 'react-native';
import {  useRouter } from 'expo-router';
import { useState } from 'react';
import { useAppContext } from '../AppContext';

export default function ScreenB() {
  const router = useRouter();
  const { updateDataFromB } = useAppContext();
  const [inputText, setInputText] = useState('');

  const goBackAndSendData = () => {
    updateDataFromB(inputText);
    router.back();
  };

  return (
    <View>
      <Text>Enter data to send back to A:</Text>
      <TextInput onChangeText={setInputText} value={inputText} />
      <Button title="Send Data and Go Back" onPress={goBackAndSendData} />
    </View>
  );
}

In this example, Screen B has a TextInput where the user can enter some text. When the user presses the