Embedding a C library and its dependencies into a Flutter iOS app: A Step-by-Step Guide

Step 1: Create a new Flutter project

Let’s start by creating a new Flutter project using the command:

flutter create my_app

This will create a new directory called `my_app` with the basic structure for a Flutter project.

Step 2: Add the C library and its dependencies to the project

Next, we need to add the C library and its dependencies to our project. There are several ways to do this, depending on the nature of the library and its dependencies.

Option 1: Add the C library and its dependencies as source code

If you have the source code for the C library and its dependencies, you can add them to your project by creating a new directory called `c_src` inside the `ios` directory:

mkdir ios/c_src

Then, add the source code files for the C library and its dependencies to this directory.

Option 2: Add the C library and its dependencies as pre-built binaries

If you have pre-built binaries for the C library and its dependencies, you can add them to your project by creating a new directory called `c_libs` inside the `ios` directory:

mkdir ios/c_libs

Then, add the pre-built binaries for the C library and its dependencies to this directory.

Step 3: Create a Swift wrapper for the C library

To use the C library from Swift, we need to create a Swift wrapper that exposes the functionality of the C library. Create a new file called `CLibrary.swift` inside the `ios/Flutter` directory:

touch ios/Flutter/CLibrary.swift

Then, add the following code to this file:

import Foundation

public class CLibrary {
    public init() {}

    public func myCFunction() {
        // Call the C function here
        my_c_function()
    }
}

private func my_c_function() {
    // Load the C library and its dependencies
    let libPath = Bundle.main.path(forResource: "my_c_lib", ofType: "dylib")!
    let libHandle = dlopen(libPath, RTLD_LAZY)

    // Get the address of the C function
    let sym = dlsym(libHandle, "my_c_function")
    let funcPtr = sym!.assumingMemoryBound(to: (@convention(c) () -> Void).self)

    // Call the C function
    funcPtr()
}

This code defines a Swift class called `CLibrary` that exposes a single function called `myCFunction`. This function loads the C library and its dependencies, gets the address of the C function, and calls it.

Step 4: Use the Swift wrapper from Dart

To use the Swift wrapper from Dart, we need to create a platform channel that communicates with the Swift code. Create a new file called `c_library_channel.dart` inside the `lib` directory:

touch lib/c_library_channel.dart

Then, add the following code to this file:

import 'package:flutter/services.dart';

class CLibraryChannel {
  static const platform = const MethodChannel('my_app/c_library');

  Future myCFunction() async {
    await platform.invokeMethod('myCFunction');
  }
}

This code defines a Dart class called `CLibraryChannel` that uses the `MethodChannel` class to communicate with the Swift code.

Step 5: Register the platform channel

To register the platform channel, add the following code to the `ios` section of the `pubspec.yaml` file:

ios:
  flutter:
    platforms:
      ios:
        enabled: true
  platform-channel:
    CLibraryChannel: 'my_app/c_library'

Step 6: Use the C library from Dart

Finally, we can use the C library from Dart by creating an instance of the `CLibraryChannel` class and calling its `myCFunction` method:

import 'package:flutter/material.dart';
import 'package:my_app/c_library_channel.dart';

class MyApp extends StatefulWidget {
  @override
  _MyAppState createState() => _MyAppState();
}

class _MyAppState extends State {
  final CLibraryChannel _channel = CLibraryChannel();

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('My App'),
      ),
      body: Center(
        child: ElevatedButton(
          child: Text('Call C Function'),
          onPressed: () async {
            await _channel.myCFunction();
          },
        ),
      ),
    );
  }
}

This code creates a Flutter app that has a single button. When the button is pressed, it calls the `myCFunction` method on the `CLibraryChannel` instance, which in turn calls the C function using the Swift wrapper.

Conclusion

And that’s it! With these steps, you should now have a Flutter iOS app that embeds a C library and its dependencies. Remember to replace the placeholder names and paths with the actual names and paths of your C library and its dependencies.

By following this guide, you can take advantage of the performance benefits of native code and reuse existing C libraries in your Flutter iOS app. Happy coding!

Note: This article assumes that you have basic knowledge of Flutter, Dart, Swift, and C programming. If you’re new to any of these topics, you may need to do some additional research before attempting to embed a C library into your Flutter iOS app.

Frequently Asked Question

Got questions about embedding a C library and its dependencies into a Flutter iOS app? We’ve got answers! Checkout our FAQs below: