Here's a step-by-step tutorial on how to integrate the OpenAI's ChatGPT API into a React Native application. This tutorial assumes you already have a basic knowledge of JavaScript and React Native. If you're new to these technologies, consider learning them first.

Integrating ChatGPT API in React Native

Table of Contents

• Prerequisites
• Project Setup
• Installing Required Libraries
• Setting Up the ChatGPT API Service
• Creating the Chat Interface
• Connecting the Interface with the ChatGPT Service

Prerequisites

Before you start, make sure you have:

1. Node.js and npm/yarn installed on your computer. If not, download them from here.
2. The latest version of React Native CLI installed. You can install it by running npm install -g react-native-cli.
3. An OpenAI API key. You can get one from the OpenAI dashboard.

Project Setup

Start by creating a new React Native project:

npx react-native init chatGPTApp

Then, move into your project's directory:

cd chatGPTApp

Installing Required Libraries

We will be using axios for making HTTP requests to the ChatGPT API and react-native-dotenv for managing our environment variables (such as the OpenAI API key). Install these libraries with:

npm install axios @react-native-community/dotenv

Then, to setup react-native-dotenv, add the following lines to the babel.config.js:

module.exports = {
  presets: ['module:metro-react-native-babel-preset'],
  plugins: [
    ["module:react-native-dotenv"]
  ]
};

Now, create a .env file in the root directory of your project and add your OpenAI API key:

OPENAI_KEY=your_api_key_here

Setting Up the ChatGPT API Service

Create a new file named ChatGPTService.js in your project's root directory and write the following code:

import axios from 'axios';
import { OPENAI_KEY } from '@env';

const instance = axios.create({
  baseURL: 'https://api.openai.com/v1/engines/davinci-codex/completions',
  headers: {
    'Content-Type': 'application/json',
    'Authorization': `Bearer ${OPENAI_KEY}`
  }
});

export const generateResponse = async (message) => {
  try {
    const response = await instance.post('', {
      prompt: message,
      max_tokens: 60
    });
    return response.data.choices[0].text;
  } catch (error) {
    console.error(error);
    return '';
  }
};

Creating the Chat Interface

This tutorial doesn't focus on creating a sophisticated UI, so for brevity, we'll create a simple chat interface with a TextInput for the user input and a Button for sending messages.

In your App.js, replace the boilerplate code with:

import React, { useState } from 'react';
import { View, TextInput, Button, Text, ScrollView } from 'react-native';

const App = () => {
  const [messages, setMessages] = useState([]);
  const [userInput, setUserInput] = useState('');

  const sendMessage = async () => {
    // Logic to send message will go here
  };

  return (
    <View>
      <ScrollView>
        {messages.map((msg, index) => (
          <Text key={index}>{msg}</Text>
        ))}
      </ScrollView>
      <View>
        <TextInput 
          value={userInput}
          onChangeText={setUserInput}
          placeholder="Type a message"
        />
        <Button title="Send" onPress={sendMessage} />
      </View>
    </View>
  );
};

export default App;

Connecting the Interface with the ChatGPT Service

Finally, we need to connect our chat interface with the ChatGPT service. Modify the sendMessage function in App.js to:

import { generateResponse } from './ChatGPTService';

// ...previous code

const sendMessage = async () => {
  if (!userInput) return;

  setMessages(prevMessages => [...prevMessages, `User: ${userInput}`]);
  const botResponse = await generateResponse(userInput);
  setMessages(prevMessages => [...prevMessages, `ChatGPT: ${botResponse}`]);
  setUserInput('');
};

That's it! You now have a React Native application integrated with the ChatGPT API. You can run your app using npx react-native run-android or npx react-native run-ios depending on your target platform.

Remember to keep your API key secure and do not expose it on the client-side in a real-world application. It's recommended to setup a backend server that communicates with the OpenAI API, and your React Native application should communicate with this server.

If you are interested in skipping all these steps and get a ready to use template, check out this premium React Native ChatGPT app offered by Instamobile.