Using Pigeon for Flutter Development on HarmonyOS

在鸿蒙中开发Flutter项目，一个最大的问题，就是“不太会写鸿蒙代码”，这对于一个Flutter开发者来说，虽然不是一件很麻烦的事，但由于现在鸿蒙的版本和文档还略有一些混乱，所以要写好还是有一些麻烦的，所以，秉着能用工具解决的问题就不要自己写的原则，我们参考Native的Flutter Channel的实现，也就是pigeon的方式，不熟悉的同学可以参考我之前的文章。

Flutter混编工程之高速公路Pigeon

这套东西在鸿蒙中也有的适配，可以一键生成ets代码，方便我们进行多端复用，项目地址如下。

https://gitee.com/openharmony-sig/flutter_packages/tree/master/packages/pigeon

在鸿蒙中使用也非常简单，指定引用即可，代码如下所示。

yaml
pigeon:
git:
url: "https://gitee.com/openharmony-sig/flutter_packages.git"
path: "packages/pigeon"

pub get之后，参考我们之前的实现，创建一个接口协议文件，这里就用之前的来示例。

dart
import 'package:pigeon/pigeon.dart';
@HostApi()
abstract class NativeNetApi {
@async
String
getNativeNetBridge(
String
path,
Map
<
String
,
Object
> params);
@async
String
postNativeNetBridge(
String
path,
Map
<
String
,
Object
> params);
void
doActionUrlCall(
String
actionUrl);
}

接下来执行命令：

shell
flutter pub run pigeon --input lib/native_api.dart --arkts_out lib/native_channel.ets --dart_out lib/native_channel.dart

执行完成后，就会在指定目录下生成我们需要的Channel文件，dart代码我就不贴了，和之前文章中的一样，我们来看下鸿蒙的代码。

arkts
import StandardMessageCodec from '@ohos/flutter_ohos/src/main/ets/plugin/common/StandardMessageCodec';
import BasicMessageChannel, { Reply } from '@ohos/flutter_ohos/src/main/ets/plugin/common/BasicMessageChannel';
import { BinaryMessenger,TaskQueue } from '@ohos/flutter_ohos/src/main/ets/plugin/common/BinaryMessenger';
import MessageCodec from '@ohos/flutter_ohos/src/main/ets/plugin/common/MessageCodec';
import { ByteBuffer } from '@ohos/flutter_ohos/src/main/ets/util/ByteBuffer';
/** Error class for passing custom error details to Flutter via a thrown PlatformException. */
export class FlutterError implements Error {
/** The error code. */
public code: string;
/** The error name. */
public name: string;
/** The error message. */
public message: string;
/** The error stack. */
public stack?: string;
constructor(code: string, name: string,  message: string, stack: string)
{
this.code = code;
this.name = name;
this.message = message;
this.stack = stack;
}
}
function wrapError(error: Error): Array<Object> {
let errorList: Array<Object> = new Array<Object>(3);
if (error instanceof FlutterError) {
let err: FlutterError = error as FlutterError;
errorList[0] = err.code;
errorList[1] = err.name;
errorList[2] = err.message;
} else {
errorList[0] = error.toString();
errorList[1] = error.name;
errorList[2] = "Cause: " + error.message + ", Stacktrace: " + error.stack;
}
return errorList;
}
export interface Result<T> {
success( result: T ): void;
error( error: Error): void;
}
/* Generated abstract class from Pigeon that represents a handler of messages from Flutter.*/
export abstract class NativeNetApi {
abstract getNativeNetBridge(path: string , params: Map<string, Object> , result: Result<string>): void;
abstract postNativeNetBridge(path: string , params: Map<string, Object> , result: Result<string>): void;
abstract doActionUrlCall(actionUrl: string ): void;
/** The codec used by NativeNetApi. */
static getCodec(): MessageCodec<Object>{
return new StandardMessageCodec();
}
/*Sets up an instance of `NativeNetApi` to handle messages through the `binaryMessenger`.*/
static setup(binaryMessenger: BinaryMessenger, api: NativeNetApi | null): void {
{
let channel: BasicMessageChannel<Object> =
new BasicMessageChannel(
binaryMessenger, "dev.flutter.pigeon.test1.NativeNetApi.getNativeNetBridge", NativeNetApi.getCodec());
if (api != null) {
channel.setMessageHandler({
onMessage(message: Object ,reply: Reply<Object> ) {
let args: Array<Object> = message as Array<Object>;
class ResultImp implements Result<string>{
success(result: string): void {
let res: Array<Object> = [];
res.push(result);
reply.reply(res);
}
error(error: Error): void {
let wrappedError: Array<Object> = wrapError(error);
reply.reply(wrappedError);
}
}
let resultCallback: Result<string> = new ResultImp();
api!.getNativeNetBridge(args[0] as string, args[1] as Map<string, Object>, resultCallback);
} });
} else {
channel.setMessageHandler(null);
}
}
{
let channel: BasicMessageChannel<Object> =
new BasicMessageChannel(
binaryMessenger, "dev.flutter.pigeon.test1.NativeNetApi.postNativeNetBridge", NativeNetApi.getCodec());
if (api != null) {
channel.setMessageHandler({
onMessage(message: Object ,reply: Reply<Object> ) {
let args: Array<Object> = message as Array<Object>;
class ResultImp implements Result<string>{
success(result: string): void {
let res: Array<Object> = [];
res.push(result);
reply.reply(res);
}
error(error: Error): void {
let wrappedError: Array<Object> = wrapError(error);
reply.reply(wrappedError);
}
}
let resultCallback: Result<string> = new ResultImp();
api!.postNativeNetBridge(args[0] as string, args[1] as Map<string, Object>, resultCallback);
} });
} else {
channel.setMessageHandler(null);
}
}
{
let channel: BasicMessageChannel<Object> =
new BasicMessageChannel(
binaryMessenger, "dev.flutter.pigeon.test1.NativeNetApi.doActionUrlCall", NativeNetApi.getCodec());
if (api != null) {
channel.setMessageHandler({
onMessage(message: Object ,reply: Reply<Object> ) {
let args: Array<Object> = message as Array<Object>;
let res: Array<Object> = [];
try {
api!.doActionUrlCall(args[0] as string);
res.push(null);
}
catch (error) {
let wrappedError: Array<Object> = wrapError(error);
res = wrappedError;
}
reply.reply(res);
} });
} else {
channel.setMessageHandler(null);
}
}
}
}
}

整体代码和Java的代码很类似，阅读基本没什么障碍，使用方式也和Native保持一致，通过调用setup方法，传入接口的实现即可，这里就不赘述了。

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