Flutter C/C++集成插件flutter_ccpp的使用

当然，以下是一个关于如何在Flutter项目中集成并使用C/C++插件flutter_ccpp的示例代码和步骤。这个示例将展示如何在Flutter应用中调用C/C++编写的原生代码。

前提条件

1. 确保你已经安装了Flutter开发环境。
2. 确保你熟悉Dart和Flutter的基本操作。

步骤一：创建Flutter插件项目

首先，你需要创建一个Flutter插件项目，如果还没有的话。

flutter create my_flutter_app
cd my_flutter_app

步骤二：添加flutter_ccpp插件

由于flutter_ccpp是一个假想的插件名称，实际中你可能需要创建一个自定义的Flutter插件或使用现有的Flutter插件。这里假设你已经有一个名为flutter_ccpp的插件。

在pubspec.yaml文件中添加依赖：

dependencies:
  flutter:
    sdk: flutter
  flutter_ccpp:
    path: ../path_to_your_flutter_ccpp_plugin  # 如果是本地插件
    # 或者使用远程路径或版本
    # version: ^x.y.z

步骤三：编写C/C++代码

假设你的flutter_ccpp插件需要实现一个简单的加法函数。在插件的ios和android目录下分别编写C/C++代码。

iOS

在ios/Classes目录下创建一个native_code.cpp文件：

// native_code.cpp
#include <jni.h>
#include <flutter/method_channel.h>
#include <string>

extern "C" {
    __attribute__((visibility("default")))
    int32_t add(int32_t a, int32_t b) {
        return a + b;
    }
}

在ios/Classes/FlutterCcppPlugin.mm文件中注册方法通道并调用C/C++代码：

#import <Flutter/Flutter.h>
#import "native_code.cpp"

@interface FlutterCcppPlugin : NSObject<FlutterPlugin>
@end

@implementation FlutterCcppPlugin
+ (void)registerWithRegistrar:(NSObject<FlutterPluginRegistrar>*)registrar {
    FlutterMethodChannel* channel = [FlutterMethodChannel
                                     methodChannelWithName:@"flutter_ccpp"
                                     binaryMessenger:registrar.messenger];
    __weak typeof(self) weakSelf = self;
    [channel setMethodCallHandler:^(FlutterMethodCall* call, FlutterResult result) {
      if ([@"add" isEqualToString:call.method]) {
        NSNumber *num1 = call.arguments[@"a"];
        NSNumber *num2 = call.arguments[@"b"];
        int32_t a = [num1 intValue];
        int32_t b = [num2 intValue];
        int32_t sum = add(a, b);
        result(@(sum));
      } else {
        result(FlutterMethodNotImplemented);
      }
    }];
}
@end

Android

在android/src/main/cpp目录下创建一个CMakeLists.txt文件和一个native_code.cpp文件。

CMakeLists.txt:

cmake_minimum_required(VERSION 3.4.1)

add_library(
            native-lib
            SHARED
            native_code.cpp)

find_library(
            log-lib
            log)

target_link_libraries(
            native-lib
            ${log-lib})

native_code.cpp:

#include <jni.h>
#include <string>

extern "C" JNIEXPORT jint JNICALL
Java_com_example_flutterccpp_NativeLib_add(JNIEnv* env, jobject /* this */, jint a, jint b) {
    return a + b;
}

在android/src/main/java/com/example/flutterccpp目录下创建一个NativeLib.java文件：

package com.example.flutterccpp;

public class NativeLib {
    static {
        System.loadLibrary("native-lib");
    }

    public native int add(int a, int b);
}

在android/src/main/kotlin/com/example/flutterccpp/FlutterCcppPlugin.kt（或Java）中注册方法通道并调用C/C++代码：

package com.example.flutterccpp

import io.flutter.embedding.engine.plugins.FlutterPlugin
import io.flutter.embedding.engine.plugins.activity.ActivityAware
import io.flutter.embedding.engine.plugins.activity.ActivityPluginBinding
import io.flutter.plugin.common.MethodCall
import io.flutter.plugin.common.MethodChannel
import io.flutter.plugin.common.MethodChannel.MethodCallHandler
import io.flutter.plugin.common.MethodChannel.Result
import android.app.Activity
import android.content.Context

class FlutterCcppPlugin: FlutterPlugin, MethodCallHandler, ActivityAware {
  private lateinit var channel: MethodChannel
  private var context: Context? = null

  override fun onAttachedToEngine(binding: FlutterPluginBinding) {
    channel = MethodChannel(binding.binaryMessenger, "flutter_ccpp")
    channel.setMethodCallHandler(this)
    context = binding.applicationContext
  }

  override fun onMethodCall(call: MethodCall, result: Result) {
    if (call.method == "add") {
      val a = call.argument<Int>("a") ?: 0
      val b = call.argument<Int>("b") ?: 0
      val sum = NativeLib().add(a, b)
      result.success(sum)
    } else {
      result.notImplemented()
    }
  }

  override fun onDetachedFromEngine(binding: FlutterPluginBinding) {
    channel.setMethodCallHandler(null)
  }

  override fun onAttachedToActivity(binding: ActivityPluginBinding) {
    binding.addActivityResultListener(this)
  }

  override fun onDetachedFromActivityForConfigChanges() {
    // No-op
  }

  override fun onReattachedToActivityForConfigChanges(binding: ActivityPluginBinding) {
    // No-op
  }

  override fun onDetachedFromActivity() {
    // No-op
  }
}

步骤四：在Flutter中调用C/C++代码

在你的Flutter项目中，你可以通过方法通道调用C/C++代码。在lib/main.dart文件中：

import 'package:flutter/material.dart';
import 'package:flutter/services.dart';
import 'package:flutter_ccpp/flutter_ccpp.dart'; // 假设有这样一个导入

void main() {
  runApp(MyApp());
}

class MyApp extends StatelessWidget {
  static const platform = MethodChannel('flutter_ccpp');

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: Scaffold(
        appBar: AppBar(
          title: const Text('Flutter C/C++ Integration'),
        ),
        body: Center(
          child: ElevatedButton(
            onPressed: _invokeNativeAdd,
            child: Text('Invoke Native Add'),
          ),
        ),
      ),
    );
  }

  Future<void> _invokeNativeAdd() async {
    try {
      final int result = await platform.invokeMethod('add', <String, dynamic>{'a': 10, 'b': 20});
      print("Result: $result");
    } on PlatformException catch (e) {
      print("Failed to invoke: '${e.message}'.");
    }
  }
}

注意事项

1. 上述代码示例仅作为演示，实际项目中需要根据具体需求进行调整。
2. 确保在iOS和Android平台上分别正确配置了CMake和NDK（如果适用）。
3. 确保插件的注册和调用方法通道的代码正确无误。

通过以上步骤，你可以在Flutter应用中集成并使用C/C++编写的原生代码。