本文介绍从dart中，通过ffi方式调用golang生成的动态链接库。

go/lib.go

package mainimport "C"//export GetKey
func GetKey() *C.char {theKey := "123-456-789"return C.CString(theKey)
}func main() {}

cd go
go build -buildmode=c-shared -o lib.a lib.go

如果是android上的arm64:

GOOS=android GOARCH=arm64 CGO_ENABLED=1 CC=/home/leon/app/lib/android-sdk/ndk/23.1.7779620/toolchains/llvm/prebuilt/linux-x86_64/bin/aarch64-linux-android30-clang go build -buildmode=c-shared -o libgetkey.so lib.go
$ file libgetkey.so
libgetkey.so: ELF 64-bit LSB shared object, ARM aarch64, version 1 (SYSV), dynamically linked, Go BuildID=DcPg8Sp5h2rp3UWnE6Zg/_OH6HiVNpMa5Q-1cB2k6/9fkQff1HpM8_877p07S9/Dsh4z9riT9y9DVK5HiSQ, with debug_info, not stripped

然后创建lib/checkffi.dart文件。

lib/checkffi.dart

import 'dart:ffi';
import 'dart:io' show Directory, Platform;import 'package:ffi/ffi.dart';
import 'package:path/path.dart' as path;// C function: char *GetKey();
// There's no need for two typedefs here, as both the
// C and Dart functions have the same signature
typedef HelloWorld = Pointer<Utf8> Function();getKey() {// Open the dynamic libraryvar libraryPath =path.join(Directory.current.path, 'go', 'lib.a');final dylib = DynamicLibrary.open(libraryPath);final helloWorld =dylib.lookupFunction<HelloWorld, HelloWorld>('GetKey');final message = helloWorld().toDartString();return message;
}

如果想做个测试：

lib.dart

import 'fficheck.dart';main() {print("Hello, World!");print(getKey());
}

flutter main.dartimport 'package:flutter/material.dart';
import "fficheck.dart";void main() {runApp(const MyApp());
}class MyApp extends StatelessWidget {const MyApp({super.key});// This widget is the root of your application.@overrideWidget build(BuildContext context) {return MaterialApp(title: 'Flutter Demo',theme: ThemeData(// This is the theme of your application.//// Try running your application with "flutter run". You'll see the// application has a blue toolbar. Then, without quitting the app, try// changing the primarySwatch below to Colors.green and then invoke// "hot reload" (press "r" in the console where you ran "flutter run",// or simply save your changes to "hot reload" in a Flutter IDE).// Notice that the counter didn't reset back to zero; the application// is not restarted.primarySwatch: Colors.blue,),home: const MyHomePage(title: 'Flutter Demo Home Page'),);}
}class MyHomePage extends StatefulWidget {const MyHomePage({super.key, required this.title});// This widget is the home page of your application. It is stateful, meaning// that it has a State object (defined below) that contains fields that affect// how it looks.// This class is the configuration for the state. It holds the values (in this// case the title) provided by the parent (in this case the App widget) and// used by the build method of the State. Fields in a Widget subclass are// always marked "final".final String title;@overrideState<MyHomePage> createState() => _MyHomePageState();
}class _MyHomePageState extends State<MyHomePage> {int _counter = 0;void _incrementCounter() {setState(() {// This call to setState tells the Flutter framework that something has// changed in this State, which causes it to rerun the build method below// so that the display can reflect the updated values. If we changed// _counter without calling setState(), then the build method would not be// called again, and so nothing would appear to happen._counter++;});}@overrideWidget build(BuildContext context) {// This method is rerun every time setState is called, for instance as done// by the _incrementCounter method above.//// The Flutter framework has been optimized to make rerunning build methods// fast, so that you can just rebuild anything that needs updating rather// than having to individually change instances of widgets.return Scaffold(appBar: AppBar(// Here we take the value from the MyHomePage object that was created by// the App.build method, and use it to set our appbar title.title: Text(widget.title),),body: Center(// Center is a layout widget. It takes a single child and positions it// in the middle of the parent.child: Column(// Column is also a layout widget. It takes a list of children and// arranges them vertically. By default, it sizes itself to fit its// children horizontally, and tries to be as tall as its parent.//// Invoke "debug painting" (press "p" in the console, choose the// "Toggle Debug Paint" action from the Flutter Inspector in Android// Studio, or the "Toggle Debug Paint" command in Visual Studio Code)// to see the wireframe for each widget.//// Column has various properties to control how it sizes itself and// how it positions its children. Here we use mainAxisAlignment to// center the children vertically; the main axis here is the vertical// axis because Columns are vertical (the cross axis would be// horizontal).mainAxisAlignment: MainAxisAlignment.center,children: <Widget>[const Text('You have pushed the button this many times:',),Text(getKey(),style: Theme.of(context).textTheme.headlineMedium,),],),),floatingActionButton: FloatingActionButton(onPressed: _incrementCounter,tooltip: 'Increment',child: const Icon(Icons.add),), // This trailing comma makes auto-formatting nicer for build methods.);}
}

pubspec.yaml
中增加：

dependencies:
ffi: ^1.0.0

运行：
flutter pub get
然后启动运行。

如果是在android中：

1). 需要在android/app中创建CMakeList.txt:

cmake_minimum_required(VERSION 3.4.1)  # for exampleadd_library( getkeySHAREDIMPORTEDGLOBAL
)
set_target_properties(getkey PROPERTIES IMPORTED_LOCATION ${CMAKE_CURRENT_SOURCE_DIR}/src/main/jniLibs/${ANDROID_ABI}/libgetkey.so)

本文用src/main/jniLibs/arm64-v8a/目录。

2). 在 android/app/build.gradle中添加externalNativeBuild:

android {// ...externalNativeBuild {// Encapsulates your CMake build configurations.cmake {// Provides a relative path to your CMake build script.path "CMakeLists.txt"}}//...
}

如果是C语言的源代码而不是so动态链接库，则CMakeList.txt内容参考如下：

cmake_minimum_required(VERSION 3.4.1)  # for exampleadd_library( getkey# Sets the library as a shared library.SHARED# Provides a relative path to your source file(s).src/main/c/getkey.c )

c源文件放在src/main/c/getkey.c里面

//
// Created by leon on 13/4/2023.
//
char* GetKey() {char* s = "123-456-789";return s;
}void main() {}

然后编译运行会自动生产不同架构版本的libgetkey.so，在flutter的build文件夹下面。

参考：
https://github.com/dart-lang/samples/tree/main/ffi
https://docs.flutter.dev/development/platform-integration/android/c-interop