首先官方文章有介绍基本的使用方法：官方文档

基本使用

参考文章：在 flutter 上使用 c 代码 - (一) 有源码的项目_SimpleCoder's Blog-CSDN博客_flutter 调用c代码 

1、在vscode中使用指令新建一个plugin项目：flutter create -t plugin native_add
2、在新建的native_add项目中，新建native_add.cpp文件，并放到ios/Classes/，如下图

3、native_add.cpp添加两个方法

#include <stdint.h>extern "C" {
// __attribute__((visibility("default"))) __attribute__((used))
int32_t native_add(int32_t x, int32_t y) { return x + y; }double double_add(double x, double y) { return x + y; }
}

4、在andriod目录下，新建CMakeLists.txt

cmake_minimum_required(VERSION 3.4.1)  # for exampleadd_library( native_add# Sets the library as a shared library.SHARED# Provides a relative path to your source file(s).../ios/Classes/native_add.cpp )

5、android/build.gradle文件

android{// ...externalNativeBuild {cmake {path "CMakeLists.txt"}}
}

6、在lib/native_add.dart下添加内容

import 'dart:async';import 'package:flutter/services.dart';import 'dart:ffi'; // For FFI
import 'dart:io'; // For Platform.isXfinal DynamicLibrary nativeAddLib = Platform.isAndroid? DynamicLibrary.open("libnative_add.so"): DynamicLibrary.process();final int Function(int x, int y) nativeAdd =nativeAddLib.lookup<NativeFunction<Int32 Function(Int32, Int32)>>("native_add").asFunction();class NativeAdd {static const MethodChannel _channel =const MethodChannel('native_add');static Future<String> get platformVersion async {final String version = await _channel.invokeMethod('getPlatformVersion');return version;}
}

7、在example/lib/main.dart中使用

8、在vscode的terminal窗口，使用cd example，进入native_add项目的example目录，并执行flutter run，测试是否能成功调用nativeAdd方法

9、测试结果：nativeAdd（1，2）等于3

以上就是简单的纯ffi官方的讲解介绍使用。但是在使用的过程中数据类型不仅仅是int和double，还有其他的一些问题是我遇到了并解决了的，这里给大家一些参考，希望能帮到你。

项目使用建议结合pub.dev上面的ffi和系统的ffi方法一起使用，

 

扩展以及遇到的问题及修复方案：

1. 我的c文件很多，并不是只有一个，而且c文件是已存在的，我只是创建一个交互逻辑使用它。

首先c文件还是按照之前的文件放置在ios/Classes/下面：

 

记得在CMakeLists.txt里面补充上所有的文件，注意如果是c的文件需要在公共引入方法那里导入头文件：文章参考《C++编程报错Error：Undefined reference to的常见解决办法》

extern “C”{#include “OOXX.h”}注意格式换行要正确。

否则编译会出现异常：Undefined reference to ****

 

2. 传参类型有二级指针char **

官方demo讲述的只有int，doubel的基本类型，但是c里面也存在char * 和char **的参数类型，需要用什么dart的类型来桥接？（已通过代码验证有效，尤其是char **，有些文章说使用Pointer<Uint8>，我却使用dart怎么也转换不成对应的样子。）

char *    使用Pointer<Utf8>来接。char **   使用Pointer<Pointer<Utf8>>来接

3. allocate.dart文件，一些博友留一手不上传，这里我整理了一下不需要c币的一份连接：flutter和c调用allocation.dart文件-其它文档类资源-CSDN下载https://download.csdn.net/download/BUG_delete/76844837，这个可以在ffi:0.1.2版本中找到，或则我这里给你们贴出来代码：

// Copyright (c) 2019, the Dart project authors.  Please see the AUTHORS file
// for details. All rights reserved. Use of this source code is governed by a
// BSD-style license that can be found in the LICENSE file.import 'dart:ffi';
import 'dart:io';// Note that kernel32.dll is the correct name in both 32-bit and 64-bit.
final DynamicLibrary stdlib = Platform.isWindows? DynamicLibrary.open("kernel32.dll"): DynamicLibrary.process();typedef PosixMallocNative = Pointer Function(IntPtr);
typedef PosixMalloc = Pointer Function(int);
final PosixMalloc posixMalloc =
stdlib.lookupFunction<PosixMallocNative, PosixMalloc>("malloc");typedef PosixFreeNative = Void Function(Pointer);
typedef PosixFree = void Function(Pointer);
final PosixFree posixFree =
stdlib.lookupFunction<PosixFreeNative, PosixFree>("free");typedef WinGetProcessHeapFn = Pointer Function();
final WinGetProcessHeapFn winGetProcessHeap = stdlib.lookupFunction<WinGetProcessHeapFn, WinGetProcessHeapFn>("GetProcessHeap");
final Pointer processHeap = winGetProcessHeap();typedef WinHeapAllocNative = Pointer Function(Pointer, Uint32, IntPtr);
typedef WinHeapAlloc = Pointer Function(Pointer, int, int);
final WinHeapAlloc winHeapAlloc =
stdlib.lookupFunction<WinHeapAllocNative, WinHeapAlloc>("HeapAlloc");typedef WinHeapFreeNative = Int32 Function(Pointer heap, Uint32 flags, Pointer memory);
typedef WinHeapFree = int Function(Pointer heap, int flags, Pointer memory);
final WinHeapFree winHeapFree =
stdlib.lookupFunction<WinHeapFreeNative, WinHeapFree>("HeapFree");/// Allocates memory on the native heap.
///
/// For POSIX-based systems, this uses malloc. On Windows, it uses HeapAlloc
/// against the default public heap. Allocation of either element size or count
/// of 0 is undefined.
///
/// Throws an ArgumentError on failure to allocate.
Pointer<T> allocate<T extends NativeType>({int count = 1}) {final int totalSize = count * sizeOf<T>();Pointer<T> result;if (Platform.isWindows) {result = winHeapAlloc(processHeap, /*flags=*/ 0, totalSize).cast();} else {result = posixMalloc(totalSize).cast();}if (result.address == 0) {throw ArgumentError("Could not allocate $totalSize bytes.");}return result;
}/// Releases memory on the native heap.
///
/// For POSIX-based systems, this uses free. On Windows, it uses HeapFree
/// against the default public heap. It may only be used against pointers
/// allocated in a manner equivalent to [allocate].
///
/// Throws an ArgumentError on failure to free.
///
// TODO(dartbug.com/36855): Once we have a ffi.Bool type we can use it instead
// of testing the return integer to be non-zero.
void free(Pointer pointer) {if (Platform.isWindows) {if (winHeapFree(processHeap, /*flags=*/ 0, pointer) == 0) {throw ArgumentError("Could not free $pointer.");}} else {posixFree(pointer);}
}

使用：

Pointer<Uint8> soureData = allocate<Uint8>(count:source.length);

如果你使用的时候和我一样遇到allocate方法的第一行的sizeOf<T>();提示错误，不妨可以将这个类型提出来，在外部使用的地方乘好穿进去int值就好了：可以改成如下：

使用的地方：