Bridging Native Modules in React Native

Introduction to Bridging Native Modules in React Native

Bridging Native Modules in React Native allows developers to create mobile applications using JavaScript while maintaining a single codebase for both iOS and Android. Despite this adv

antage, there are scenarios where accessing native functionality not directly available in React Native becomes necessary. In these cases, establishing a bridge between JavaScript and native code such as Objective-C/Swift for iOS or Java/Kotlin for Android is crucial. Bridging native modules enables the effective use of native features, leading to improved performance and optimized React Native development. A thorough understanding of key concepts, appropriate steps, and best practices is essential for achieving a seamless integration.

Why Use Native Modules in React Native?

Although React Native covers many common use cases with its built-in components and modules, certain features still require native code. Some examples include:

• Accessing device-specific APIs (e.g., Bluetooth, biometrics, sensors)
• Interfacing with third-party native SDKs (e.g., payments, video processing)
• Optimizing performance-critical tasks that need to run on the native thread

By bridging native modules, you can access native functionality from your JavaScript code without needing to rewrite the entire app in native languages.

Understanding the React Native Bridge

The React Native makes use of a bridge to facilitate communication in between the JavaScript code and native code. This allows the JavaScript and native code to run asynchronously. The native modules act as gateways exposing native functionality to the JavaScript.

The bridge works like this:

1. JavaScript calls a native function via the bridge.
2. The native function runs in the native environment (Java/Kotlin for Android, Objective-C/Swift for iOS).
3. The result is passed back to JavaScript through the bridge, allowing the app to continue executing on the JavaScript side.

Two Key Points to Understand:

• Asynchronous Communication: The bridge doesn’t block the JavaScript thread, meaning native operations (which may take time) don’t slow down the UI.
• Marshaling Data: Data passed between JavaScript and native code needs to be marshaled (or converted). For instance, complex data types (like arrays or objects) need to be serialized to be passed through the bridge.

Creating a Native Module in iOS (Swift)

Let’s start by creating a native module for iOS using Swift.

Step 1: Setting Up the Native Code

1. Open your iOS project in Xcode: Open the ios directory of your React Native project in Xcode.
2. Create a Swift file:
   • Select your project, right-click on the folder containing the code (YourAppName > New File).
   • Choose Swift File, give it a name (e.g., CustomModule.swift), and add it to your project.
3. Configure Bridging Header: When prompted to create a Bridging Header, accept it. This allows your Swift code to communicate with Objective-C, which is necessary for React Native to interact with your Swift module.

Step 2: Implement the Native Module in Swift

import Foundation
import React

@objc(CustomModule)
class CustomModule: NSObject {
  
  // Expose method to React Native
  @objc
  func showMessage(_ message: String, callback: RCTResponseSenderBlock) {
    // Perform native functionality (e.g., showing a native alert)
    let alert = UIAlertController(title: "React Native", message: message, preferredStyle: .alert)
    alert.addAction(UIAlertAction(title: "OK", style: .default, handler: nil))
    
    // Pass data back to JavaScript
    callback(["Success"])
  }
  
  // Indicate to React Native that this module needs to be initialized
  @objc static func requiresMainQueueSetup() -> Bool {
    return true
  }
}

Step 3: Register the Module

Next, we need to tell React Native that our native module exists.

1. Open YourAppName > ios > YourAppName > YourAppName-Bridging-Header.h.
2. Add the following import statement:

#import <React/RCTBridgeModule.h>

In the CustomModule.swift, the native method showMessage is exposed to JavaScript, and React Native can call this method using the bridge.

Step 4: Expose the Native Module to JavaScript

Create a file named CustomModule.js in your React Native project.

import { NativeModules } from 'react-native';

const { CustomModule } = NativeModules;

export default CustomModule;

Now, you can call your native iOS functionality directly from JavaScript.

Example Usage:

import React from 'react';
import { Button, View } from 'react-native';
import CustomModule from './CustomModule';

const App = () => {
  const showMessage = () => {
    CustomModule.showMessage('Hello from React Native!', (result) => {
      console.log(result); // logs "Success"
    });
  };

  return (
    <View>
      <Button title="Show Native Alert" onPress={showMessage} />
    </View>
  );
};

export default App;

Creating a Native Module in Android (Java/Kotlin)

Now let’s look at how to create a native module for Android.

Step 1: Setting Up the Native Code

1. Open your Android project in Android Studio: Open the android directory of your React Native project.
2. Create a Java class for your native module: In android/app/src/main/java/com/yourappname/, create a new Java class (e.g., CustomModule.java).

Step 2: Implement the Native Module in Java

package com.yourappname;

import android.widget.Toast;
import com.facebook.react.bridge.ReactApplicationContext;
import com.facebook.react.bridge.ReactContextBaseJavaModule;
import com.facebook.react.bridge.ReactMethod;
import com.facebook.react.bridge.Callback;

public class CustomModule extends ReactContextBaseJavaModule {

    CustomModule(ReactApplicationContext context) {
        super(context);
    }

    @Override
    public String getName() {
        return "CustomModule";
    }

    @ReactMethod
    public void showMessage(String message, Callback callback) {
        // Show a native toast
        Toast.makeText(getReactApplicationContext(), message, Toast.LENGTH_LONG).show();
        
        // Call the JavaScript callback
        callback.invoke("Success");
    }
}

Step 3: Register the Module

Next, you need to register the native module so React Native can access it. Create a new file called CustomPackage.java in the same directory:

package com.yourappname;

import com.facebook.react.ReactPackage;
import com.facebook.react.bridge.NativeModule;
import com.facebook.react.bridge.ReactApplicationContext;
import com.facebook.react.uimanager.ViewManager;

import java.util.ArrayList;
import java.util.Collections;
import java.util.List;

public class CustomPackage implements ReactPackage {

    @Override
    public List<NativeModule> createNativeModules(ReactApplicationContext reactContext) {
        List<NativeModule> modules = new ArrayList<>();
        modules.add(new CustomModule(reactContext));
        return modules;
    }

    @Override
    public List<ViewManager> createViewManagers(ReactApplicationContext reactContext) {
        return Collections.emptyList();
    }
}

Step 4: Link the Native Module in MainApplication.java

Open MainApplication.java and add the custom package:

@Override
protected List<ReactPackage> getPackages() {
    return Arrays.<ReactPackage>asList(
        new MainReactPackage(),
        new CustomPackage() // Add this line
    );
}

Advantages of Bridging Native Modules in React Native

Bridging native modules in React Native offers developers the flexibility to integrate platform-specific functionality and harness the full potential of native APIs. This allows React Native apps to achieve near-native performance and access features not available through JavaScript alone. Here are the key advantages of bridging native modules in React Native:

1. Access to Native Functionality

• Platform-Specific Features: Bridging enables React Native developers to access native functionality, such as device hardware (camera, GPS, etc.) or platform-specific APIs, that may not be available through React Native’s JavaScript APIs.
• Greater Customization: It allows developers to write custom native code (in Java, Kotlin, Swift, or Objective-C) to meet specific application needs, providing a higher level of control over the app’s behavior.

2. Improved Performance

• Native-Level Performance: For performance-critical tasks such as complex animations, heavy computations, or intensive data processing, bridging to native modules can bypass the limitations of JavaScript, delivering faster and more responsive app performance.
• Optimized Code: By leveraging the efficiency of native code, developers can reduce the execution time of certain features, improving the overall responsiveness and performance of the app.

3. Reuse of Existing Native Code

• Leverage Existing Libraries: Bridging allows developers to reuse existing native libraries and frameworks, making it easier to integrate proven native solutions without having to rewrite the entire functionality in JavaScript.
• Preserve Legacy Code: If an organization already has a well-established native codebase, React Native’s bridging mechanism allows them to reuse that code without significant rework, reducing development time and effort.

4. Enhanced Flexibility

• Custom Solutions: When a specific feature or module is not available in React Native’s ecosystem, developers can build their own native modules. This provides the flexibility to create custom solutions tailored to the app’s unique requirements.
• Future-Proofing: As new native features are introduced by Android and iOS, developers can immediately access and integrate these features into their React Native applications via bridging, even before official support is available in the React Native library.

5. Integration with Platform-Specific APIs

• Access to Native SDKs: Many third-party services offer SDKs for iOS and Android. Bridging allows developers to integrate these SDKs seamlessly into a React Native app, unlocking advanced functionalities like push notifications, in-app purchases, or authentication.
• Hardware-Level Access: Bridging enables direct access to device hardware, such as the camera, sensors, Bluetooth, or biometrics (like Face ID or fingerprint recognition), expanding the scope of what the app can do.

6. Better User Experience

• Smoother Animations and Interactions: Bridging can provide a smoother user experience by utilizing native APIs for animations, gesture handling, or transitions, which are often faster and more efficient than their JavaScript counterparts.
• Platform-Specific Optimizations: By using native code, developers can tailor their app’s user experience to better align with the design conventions and performance expectations of each platform (iOS or Android), improving the overall app experience.

7. Expanded Ecosystem

• Broader Toolset: Bridging allows React Native developers to tap into the broader ecosystem of native development, using tools and libraries that are well-established in the native mobile development space.
• Native Code Communities: Developers can also leverage the expertise and solutions of native development communities (such as iOS or Android developers), enhancing the resources available for problem-solving and feature implementation.

8. Native Module Sharing

• Reusable Modules: Once a native module is created for a specific app, it can be reused across multiple React Native projects, making it easier to share and maintain commonly used functionalities.
• Community Modules: Many developers and organizations contribute their native modules to the React Native ecosystem. These can be used by other developers without the need to write their own native code from scratch.

9. Extending React Native’s Capabilities

• Filling Gaps in React Native: Bridging allows developers to extend React Native’s capabilities when certain features or APIs are missing or not performant enough in JavaScript. This empowers teams to build fully-featured applications without waiting for React Native’s core team to implement every feature.
• Rapid Prototyping: By bridging specific native functionality, developers can rapidly prototype features using a combination of JavaScript and native code, enabling faster testing and iteration.

10. Seamless Cross-Platform Experience

• Unified JavaScript and Native Integration: With bridging, developers can combine the flexibility of JavaScript for logic and UI development with the power of native code for performance-critical features. This results in a seamless cross-platform experience while leveraging the strengths of each technology.
• Consistency Across Platforms: Bridging ensures that the same functionality is available on both Android and iOS with minimal effort, making it easier to maintain a consistent user experience across different platforms.

Disadvantages of Bridging Native Modules in React Native

This native modules bridge in React Native enables programmers to access more features, which are achievable only on a specific platform, and boosts performance but presents various issues. These disadvantages reflect the trade-offs that developers must make when opting to implement native code within a React Native application. The main disadvantages include the following:

1. Increased Development Complexity

• Greater Learning Curve: The bride requires developers to be abreast with both React Native JavaScript and native languages such as Android Java or Kotlin and Objective C/Swift for iOS. This would, therefore result in a greater learning curve for development.
• Context Switching: Developers have to switch between various programming environments; for instance, JavaScript for React Native and native languages, which slows down the development and makes debugging increasingly complex.

2. Maintenance of Platform-specific code

• Multi Code Bases for Android and iOS: Bridging requires authors to write and maintain separate native code for Android and iOS, making it therefore more burdensome to maintain. In addition to that, updates, bug fixes, and feature additions must be individually handled on each platform.
• Version Incompatibility: As React Native or native SDKs update, there is a risk that native modules, which were previously working, will break due to the version incompatibility, requiring frequent updates and testing.

3. Reduced Cross-Platform Consistency

• Non-Uniform Codebase: Though the ability to share code across platforms is one of the main benefits of React Native, bridging imposes a certain amount of platform-specific code that breaks this uniformity. It implies an approach that’s less uniform in development.
• Different Behaviors on different Platforms: Native modules might behave differently on Android and iOS. This has led to inconsistency in the ways apps work or even look on both platforms, making it tough for the user.

4. Debugging Challenges

• More Challenging Debugging: debugging of native modules using a bridge is often more challenging than JavaScript code. Sometimes, an error might be in the interaction between JavaScript and native code; thus, the developers may have to debug both their JavaScript as well as native parts of the app.
• Lack of Standard Debugging Tools: The debugging tools in JavaScript by React Native are of great quality, but native code also often needs to be debugged using platform-specific tools (e.g., Xcode for iOS and Android Studio for Android), which makes it more cumbersome to identify issues and then correct them.

5. Overhead in terms of Performance

• Communication Overhead: Bridging between JavaScript and native modules always results in performance overhead due to the need to serialize data and perform asynchronous communication between two different environments. This could add latency to your app, especially when relying on heavy interactions between JavaScript and native code.
• High Consumption of Memory: Bridging also increases memory consumption; this can happen in apps that often pass large amounts of data around between the JavaScript and native layers.

6. Difficult Testing and Debugging for Edge Cases

• Platform-Specific Bugs:Testing and Debugging for Edge Cases Bugs Native code can exhibit platform-specific bugs that may not be caught up by React Native. Bugs like that are often not easy to reproduce, considering one app may run in emulators and real devices.
• Complex Unit Testing: Unit testing of bridged native modules can be complex. For a developer, that also means establishing a testing environment of native code, aside from the JavaScript logic to be tested.

7. Increased Development Time

• Longer Cycles: With native code implementation both for Android and iOS on the part of the developer, development time for bridged solutions can be significantly more in duration compared to purely JavaScript-based solutions.
• Slower Prototyping: The need to implement native code slows down rapid prototyping and iteration, one of the key advantages of using React Native.

8. Scope for Technical Debt

• Native Code Build-Up: Native code can build up, gradually raising the technical debt of the project. If too many native modules get relied on by your app, some of the cross-platform capabilities provided by the benefits of React Native might be lost, and the application might ultimately turn into a hybrid app complicated by maintenance needs.
• Native Code Maintenance Dependency: If the third-party libraries include native modules, it might make your project dependent on the group of external developers who need to support and update those modules for Android or iOS changes, leading to delays and problems.

9. Dependency on Native Expertise

• Native Developers: An application that heavily requires bridging for React Native would require developers with experience both in Android and iOS. It might spike the cost of resources and prove difficult in terms of staffing; especially for a small-scale team.
• Difficulty in Hiring: There is a significant difficulty in finding the right candidates who have enough experience in both React Native and native development; one needs to find those who can code JavaScript and Android and iOS ecosystems.

10. Compatibility Issue

• Version Incompatibility Between React Native and Native SDKs: The bridging modules will be version-incompatible with later versions of React Native, or native SDKs. That would take extra development time to solve the issues due to the versioning compatibility problem
• Deprecation: Native APIs, or libraries might be deprecated and hence future unsupported considering changes in iOS and Android. This usually requires quite a lot of refactoring, or rework on the native codebase

11. Scaling Challenges

• Scaling Challenges: As the count of native modules increases, it challenges the maintainability and testing, as well as up-gradation of the codebase. This makes the development process slow and makes the project quite tough to scale up.
• Fragmentation: As soon as the native code is added to the project, fragmentation increases in the codebase. This may eventually be inefficient in terms of development and deployment and increases bugs and inconsistencies.