Unlocking the Power of Native Libraries in Flutter with Dart FFI

What is Dart FFI?

Dart FFI (Foreign Function Interface) is a mechanism that enables programs written in one language to call libraries written in other languages. This means you can write code in any language that compiles to a C library, such as Go or Rust, and then expose it to a Flutter app using FFI. The benefits of this approach are twofold: you can reuse existing native code and leverage the performance and functionality of native libraries in your Flutter app.

Using Dart FFI to Access Native Libraries

To demonstrate the power of Dart FFI, let’s start with a simple example. Suppose we want to write a basic math function in C and then use it in a Dart application. We’ll begin by writing the C code and compiling it into a dynamic library. Then, we’ll use Dart FFI to call the function from our Dart app.

// math_library.c
int add(int a, int b) {
    return a + b;
}

Next, we’ll compile the C code into a dynamic library using a compiler such as GCC:

gcc -shared -o libmath_library.so math_library.c

Generating FFI Bindings with FFIGEN

While it’s possible to write FFI binding code by hand, it can be a tedious and time-consuming process. That’s where FFIGEN comes in – a tool that generates FFI bindings for you. With FFIGEN, you can automatically generate Dart code from C headers, making it easier to integrate native libraries into your Flutter app.

// Generated FFI binding code
final DynamicLibrary _library = DynamicLibrary.open('libmath_library.so');

int add(int a, int b) {
  return _library.lookup<nativefunction>('add').asFunction();
}
</nativefunction

A Demo: Using FFIGEN to Integrate cJSON into a Flutter App

To illustrate the power of FFIGEN, let’s walk through a demo that integrates the cJSON library into a Flutter app. We’ll start by generating the dynamic library using CMake, then use FFIGEN to generate the FFI binding code. Finally, we’ll load the library and use it to parse JSON data in our Flutter app.

// Import the generated FFI binding code
import 'package:cjson/cjson.dart';

void main() {
  // Load the cJSON library
  final DynamicLibrary _library = DynamicLibrary.open('libcjson.so');

  // Parse JSON data using cJSON
  final jsonString = '{"name": "John", "age": 30}';
  final cJSON *json = cJSON_Parse(jsonString);
  //...
}

Using FFI to Add a Dynamic Library to a Flutter App

So far, we’ve seen how to use Dart FFI to access native libraries in a Dart application. But what about Flutter apps? The good news is that most of the concepts we’ve covered apply to Flutter as well. To add a dynamic library to a Flutter app using FFI, we’ll need to:

• Configure the Android Studio C compiler: Update the `android/build.gradle` file to include the NDK and CMake.
• Configure the Xcode C compiler: Update the `ios/Podfile` file to include the CocoaPods and CMake.
• Generate the FFI binding code: Use FFIGEN to generate the Dart code from the C headers.
• Load the library: Use the `DynamicLibrary` class to load the dynamic library in your Flutter app.
• Test the call in Flutter: Call the native function from your Flutter app and verify that it works as expected.

By following these steps, you can unlock the power of native libraries in your Flutter app and take it to new heights.