在 flutter 上使用 c 代码 - (一) 有源码的项目

1void hello_world()
2{
3    printf("Hello World\n");
4}

1import 'dart:ffi' as ffi;

 1// 定义一个ffi类型
 2typedef hello_world_func = ffi.Void Function();
 3
 4// 将ffi类型定义为dart类型
 5typedef HelloWorld = void Function();
 6
 7// 打开动态库, dylib是mac上的动态库的后缀
 8final dylib = ffi.DynamicLibrary.open('hello_world.dylib');
 9
10// 这里是最难理解的一步, 后面会详细解说
11final HelloWorld hello = dylib
12    .lookup<ffi.NativeFunction<hello_world_func>>('hello_world')
13    .asFunction();
14
15// 调用
16hello();

1external Pointer<T> lookup<T extends NativeType>(String symbolName);

1
2/// 定义是这样的
3void Function()
4
5/// 接收的asFunction方法
6final void Function() hello = XXXX;

1extern "C" {
2// __attribute__((visibility("default"))) __attribute__((used)) // 虽然说需要这行, 但是没这行也没报错
3int32_t native_add(int32_t x, int32_t y) { return x + y; }
4
5double double_add(double x, double y) { return x + y; }
6}

 1import 'dart:ffi';
 2
 3final DynamicLibrary dylib = Platform.isAndroid
 4    ? DynamicLibrary.open("libnative_add.so")
 5    : DynamicLibrary.open("native_add.framework/native_add");
 6
 7final int Function(int x, int y) nativeAdd = dylib
 8    .lookup<NativeFunction<Int32 Function(Int32, Int32)>>("native_add")
 9    .asFunction();
10
11final double Function(double, double) doubleAdd = dylib
12    .lookup<NativeFunction<Double Function(Double, Double)>>("double_add")
13    .asFunction();

1#include <stdint.h>
2
3extern "C" {
4// __attribute__((visibility("default"))) __attribute__((used))
5int32_t native_add(int32_t x, int32_t y) { return x + y; }
6
7double double_add(double x, double y) { return x + y; }
8}

 1final DynamicLibrary dylib = Platform.isAndroid
 2    ? DynamicLibrary.open("libnative_add.so")
 3    : DynamicLibrary.open("native_add.framework/native_add");
 4
 5final int Function(int x, int y) nativeAdd = dylib
 6    .lookup<NativeFunction<Int32 Function(Int32, Int32)>>("native_add")
 7    .asFunction();
 8
 9final double Function(double, double) doubleAdd = dylib
10    .lookup<NativeFunction<Double Function(Double, Double)>>("double_add")
11    .asFunction();

 1
 2class MyHomePage extends StatefulWidget {
 3  MyHomePage({Key key, this.title}) : super(key: key);
 4
 5  final String title;
 6
 7  @override
 8  _MyHomePageState createState() => _MyHomePageState();
 9}
10
11class _MyHomePageState extends State<MyHomePage> {
12  int _counter = 0;
13
14  void _incrementCounter() {
15    setState(() {
16      _counter = nativeAdd(_counter, 1);
17    });
18  }
19
20  @override
21  Widget build(BuildContext context) {
22    return Scaffold(
23      appBar: AppBar(
24        title: Text(widget.title),
25      ),
26      body: Center(
27        child: Column(
28          mainAxisAlignment: MainAxisAlignment.center,
29          children: <Widget>[
30            Text(
31              'You have pushed the button this many times:',
32            ),
33            Text(
34              '$_counter',
35              style: Theme.of(context).textTheme.display1,
36            ),
37            Text(
38                "native double value = ${doubleAdd(_counter.toDouble(), _counter.toDouble())}"),
39          ],
40        ),
41      ),
42      floatingActionButton: FloatingActionButton(
43        onPressed: _incrementCounter,
44        tooltip: 'Increment',
45        child: Icon(Icons.add),
46      ),
47    );
48  }
49}

1s.source_files = 'Classes/**/*'

1cmake_minimum_required(VERSION 3.4.1)  # for example
2
3add_library( native_add
4
5    # Sets the library as a shared library.
6    SHARED
7
8    # Provides a relative path to your source file(s).
9    ../ios/Classes/native_add.cpp )

1android{
2    // ...
3    externalNativeBuild {
4        cmake {
5            path "CMakeLists.txt"
6        }
7    }
8}