React Native
Implementing a Native Module in Android for React Native
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Introduction
Native modules in React Native allow JavaScript to interact with Android's native functionalities. Below is an example of creating and using a custom native module in Android.
Example: Battery Level Fetcher
Android Native Code
Step 1: Create a Native Module Class Create a Java class in the Android project to define the native module.
File: BatteryModule.java
Location: android/app/src/main/java/com/yourapp/
package com.yourapp;import android.content.Intent;import android.content.IntentFilter;import android.os.BatteryManager;import com.facebook.react.bridge.ReactApplicationContext;import com.facebook.react.bridge.ReactContextBaseJavaModule;import com.facebook.react.bridge.ReactMethod;import com.facebook.react.bridge.Promise;public class BatteryModule extends ReactContextBaseJavaModule { private final ReactApplicationContext reactContext; public BatteryModule(ReactApplicationContext reactContext) { super(reactContext); this.reactContext = reactContext; } @Override public String getName() { return "BatteryModule"; } @ReactMethod public void getBatteryLevel(Promise promise) { try { IntentFilter intentFilter = new IntentFilter(Intent.ACTION_BATTERY_CHANGED); Intent batteryStatus = reactContext.registerReceiver(null, intentFilter); int level = batteryStatus.getIntExtra(BatteryManager.EXTRA_LEVEL, -1); int scale = batteryStatus.getIntExtra(BatteryManager.EXTRA_SCALE, -1); double batteryPercentage = level * 100 / (double) scale; promise.resolve(batteryPercentage); } catch (Exception e) { promise.reject("ERROR", "Could not get battery level"); } }}
Step 2: Register the Module
Add the native module to the package list.
File: MainApplication.java Location: android/app/src/main/java/com/yourapp/
import com.yourapp.BatteryModule;@Overrideprotected List<ReactPackage> getPackages() { return Arrays.<ReactPackage>asList( new MainReactPackage(), new ReactPackage() { @Override public List<NativeModule> createNativeModules(ReactApplicationContext reactContext) { return Arrays.<NativeModule>asList(new BatteryModule(reactContext)); } @Override public List<ViewManager> createViewManagers(ReactApplicationContext reactContext) { return Collections.emptyList(); } } );}
2. JavaScript Code
Step 1: Create a JavaScript Wrapper
Create a JavaScript module to interface with the native code.
File: BatteryModule.js
import { NativeModules } from 'react-native';const { BatteryModule } = NativeModules;export const getBatteryLevel = async () => { try { const batteryLevel = await BatteryModule.getBatteryLevel(); return batteryLevel; } catch (error) { console.error("Error fetching battery level:", error); throw error; }};
Step 2: Use the Module in Your React Native App
Example of how to use the battery level module in your app:
import React, { useState } from 'react';import { View, Text, Button } from 'react-native';import { getBatteryLevel } from './BatteryModule';const App = () => { const [batteryLevel, setBatteryLevel] = useState(null); const fetchBatteryLevel = async () => { try { const level = await getBatteryLevel(); setBatteryLevel(level); } catch (error) { console.error("Failed to fetch battery level:", error); } }; return ( <View style={{ flex: 1, justifyContent: 'center', alignItems: 'center' }}> <Text>Battery Level: {batteryLevel != null ? `${batteryLevel}%` : "Unknown"}</Text> <Button title="Get Battery Level" onPress={fetchBatteryLevel} /> </View> );};export default App; Advantages of Custom Native Modules in Android
- Access Native APIs: Native modules enable you to use Android-specific features not exposed by React Native.
- Performance Optimization: Direct native code execution ensures faster performance, especially for computationally intensive tasks.
- Custom Features: Implement features specific to your app’s requirements, which are unavailable in the React Native ecosystem.
- Thread Management: Perform tasks off the main thread for smooth UI updates.
- Reusable Code: Create modular components that can be reused across different projects.
- Seamless Integration: Easily combine existing Android SDKs or libraries into your React Native project.
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