In Dart, FFI (Foreign Function Interface) allows us to call native C APIs directly from Dart code, which is particularly useful when we need to perform heavy computations, access platform-specific libraries, or integrate existing native code without writing a full platform channel.
I’ve used Dart FFI primarily in Flutter projects where performance and platform integration were critical. For example, in one project, we had to perform complex image processing that was already implemented in a C++ library. Instead of rewriting everything in Dart, I used FFI to bridge the Dart layer with that native C++ library.
The process starts by creating a C library (for instance, image_utils.c) and compiling it into a shared library (.so, .dylib, or .dll, depending on the platform). In Dart, we then load that library using DynamicLibrary.open('image_utils.so'). Next, we define function signatures using typedef in both C and Dart. For example:
typedef NativeAdd = Int32 Function(Int32 a, Int32 b);
typedef DartAdd = int Function(int a, int b);
Then we can call it through:
final dylib = DynamicLibrary.open('image_utils.so');
final add = dylib.lookupFunction('add');
print(add(2, 3)); // Output: 5
One of the challenges I faced was with memory management — Dart’s garbage collector doesn’t manage native memory, so any manually allocated native resources (like using malloc) must be explicitly freed to avoid memory leaks. Also, struct alignment between Dart and C was tricky; if the data types didn’t align perfectly, it caused unexpected behavior. Using @Packed() or ensuring consistent field order solved that issue.
I applied this concept in a cross-platform Flutter app that required real-time audio processing. FFI provided much better performance than method channels because the calls are synchronous and don’t rely on serialization through platform channels.
However, one limitation is that FFI is synchronous and runs on the Dart isolate thread, so if you call a heavy native function directly, it can block the UI. To avoid that, I ran FFI calls on a background isolate or used compute() for offloading.
As an alternative, if we don’t need high performance or already have platform-specific APIs, using Flutter’s platform channels might be simpler, especially when the native integration involves Kotlin/Swift APIs instead of pure C libraries.
So, overall, FFI is a powerful choice for performance-critical and C-based integrations, but it requires careful memory handling and thread management.