Flutter 插件开发

Flutter 汇总请看这里

Flutter插件 解决什么问题

Flutter是一种跨平台框架，一套代码在Android和iOS上运行，那么当一些功能在两端需要不同的实现比如权限申请，三方api调用，这时Flutter Plugin就可以发挥作用，它包含一个用Dart编写的API定义，然后结合Android和iOS的平台不同实现。达到统一调用的目的

通信原理

消息通过platform channels在客户端（UI）和主机（platform）之间传递，如下图所示：

在Flutter层，MethodChannel(API)允许发送与方法调用相对应的消息。 在平台层面也就是Android或者iOS，Android(API)上的MethodChannel和iOS(API)上的FlutterMethodChannel启用接收方法调用并发回结果。 可以使用非常少的“样板”代码开发平台插件。

支持传递的数据类型

既然要通信，那么一下两个问题就不仅浮现在眼前
MethodChannel传递的数据支持什么类型？
Dart数据类型与Android，iOS类型的对应关系是怎样的？
结论如下：

Dart	Android	iOS
null	null	nil (NSNull when nested)
bool	java.lang.Boolean	NSNumber numberWithBool:
int	java.lang.Integer	NSNumber numberWithInt:
int if 32 bits not enough	java.lang.Long	NSNumber numberWithLong:
double	java.lang.Double	NSNumber numberWithDouble:
String	java.lang.String	NSString
Uint8List	byte[]	FlutterStandardTypedData typedDataWithBytes:
Int32List	int[]	FlutterStandardTypedData typedDataWithInt32:
Int64List	long[]	FlutterStandardTypedData typedDataWithInt64:
Float64List	double[]	FlutterStandardTypedData typedDataWithFloat64:
List	java.util.ArrayList	NSArray
Map	java.util.HashMap	NSDictionary

step1 创建插件工程

File->New->New Flutter Project 选择Flutter Plugin 起个名字一路next

此时我们创建了一个名为voice_plugin的插件

我们以工程模式打开插件工程 项目结构是这样的

我们着重了解一下以下三个文件
lib/voice_plugin.dart ——Api定义类
android/src/main/java/demo/roobo/com/voice_plugin/VoicePlugin.java ——android实现类
ios/Classes/VoicePlugin.m ——ios实现类

MethodChannel是如何交互

交互就是通过MethodChannel。MethodChannel负责dart和原生代码通信。voice_plugin是MethodChannel的名字，flutter通过一个具体的名字能才够在对应平台上找到对应的MethodChannel，从而实现flutter与平台的交互。同样地，我们在对应的平台上也要注册名为voice_plugin的MethodChannel。

lib/voice_plugin.dart

class VoicePlugin {
  static const MethodChannel _channel = const MethodChannel('voice_plugin');

  static Future<String> get platformVersion async {
    final String version = await _channel.invokeMethod('getPlatformVersion');
    return version;
  }
}

Android注册名为voice_plugin的Channel

public class VoicePlugin implements MethodCallHandler {
    private static final String TAG = "VoicePlugin";

    /**
     * Plugin registration.
     */
    public static void registerWith(Registrar registrar) {
        final MethodChannel channel = new MethodChannel(registrar.messenger(), "voice_plugin");
        channel.setMethodCallHandler(new VoicePlugin());
        Log.e(TAG, "init: mContext");
    }

    @Override
    public void onMethodCall(MethodCall call, Result result) {
        switch (call.method) {
            case "getPlatformVersion":
                result.success("Android " + android.os.Build.VERSION.RELEASE);
                break;
            default:
                result.notImplemented();
                break;
        }
    }

}

ios注册名为voice_plugin的Channel

public class SwiftVoicePlugin: NSObject, FlutterPlugin {
  public static func register(with registrar: FlutterPluginRegistrar) {
    let channel = FlutterMethodChannel(name: "voice_plugin", binaryMessenger: registrar.messenger())
    let instance = SwiftVoicePlugin()
    registrar.addMethodCallDelegate(instance, channel: channel)
  }

  public func handle(_ call: FlutterMethodCall, result: @escaping FlutterResult) {
    result("iOS " + UIDevice.current.systemVersion)
  }
}

@implementation VoicePlugin
+ (void)registerWithRegistrar:(NSObject<FlutterPluginRegistrar>*)registrar {
  [SwiftVoicePlugin registerWithRegistrar:registrar];
}
@end

至此，Flutter与原生的桥接已经完成

step2 编写Api和不同平台的实现

编写不同平台实现的时候你会发现没有提示，甚至连包依赖都找不到，而且ide在提示你 编写特定平台的代码时 你需要以工程身份打开项目 点解即可

我们打开android 工程
如下图 ：

app 是插件工程example下的android的示例程序，可以用来测试android与dart的通信

voice_plugin即android平台下实现插件api的地方

这里就像一个android工程一样 可以gradle导包 编写java或kotlin代码

首先我们在插件工程下 lib/voice_plugin.dart定义我们需要的功能 比如我们定义了register getRead getASR platformVersion等方法
在android/src/main/java/demo/roobo/com/voice_plugin/VoicePlugin.java中的onMethodCall截获这些方法获取参数并实现相应功能并且提供返回值。

//以如下方式传递参数
static Future register(String sn, String publicKey) async {
    Map<String, Object> map = {"sn": sn, "publicKey": publicKey};
    await _channel.invokeMethod('register', map);
  }
//以如下方式截获参数处理
private void registerAndInit(MethodCall call, Result result) {
       String sn = call.argument("sn");
       String publicKey = call.argument("publicKey");
       Log.e("voicePlugin", " sn:" + sn + " pbk: " + publicKey);
       init(mContext, sn, publicKey, result);
   }
//以如下方式返回数据给flutter
//Result result  result 由flutter框架创建 onMethodCall中可以得到 public void onMethodCall(MethodCall call, Result result) {}
result.success(answer.Data.pronunciation + "");

flutter插件实例

step2.1 定义api

class VoicePlugin {
  static const MethodChannel _channel = const MethodChannel('voice_plugin');

  static Future<String> get platformVersion async {
    final String version = await _channel.invokeMethod('getPlatformVersion');
    return version;
  }

  static Future register(String sn, String publicKey) async {
    Map<String, Object> map = {"sn": sn, "publicKey": publicKey};
    await _channel.invokeMethod('register', map);
  }

  static Future<String> get getASR async {
    final String result = await _channel.invokeMethod('getASR');
    return result;
  }

  static Future<String> getRead(String qa) async {
    Map<String, Object> map = {"qa": qa};

    final String result = await _channel.invokeMethod('getRead', map);
    return result;
  }
}

step2.2 实现android API

public class VoicePlugin implements MethodCallHandler {
    private static final String TAG = "VoicePlugin";
    private static Context mContext;

    /**
     * Plugin registration.
     */
    public static void registerWith(Registrar registrar) {
        final MethodChannel channel = new MethodChannel(registrar.messenger(), "voice_plugin");
        channel.setMethodCallHandler(new VoicePlugin());
        Log.e(TAG, "init: mContext");
        mContext = registrar.context();
    }

    @Override
    public void onMethodCall(MethodCall call, Result result) {
        switch (call.method) {
            case "getPlatformVersion":
                result.success("Android " + android.os.Build.VERSION.RELEASE);
                break;
            case "register":
                registerAndInit(call, result);
                break;
            case "getASR":
                onASRClick(result);
                break;
            case "getRead":
                onReadClick(call, result);
                break;
            default:
                result.notImplemented();
                break;
        }
    }

    private void registerAndInit(MethodCall call, Result result) {
        String sn = call.argument("sn");
        String publicKey = call.argument("publicKey");
        Log.e("voicePlugin", " sn:" + sn + " pbk: " + publicKey);
        init(mContext, sn, publicKey, result);
    }

   
    public void onASRClick(final Result result) {
		//这里我们调用了三方sdk获取结果
        IRooboRecognizeEngine engine = VUISDK.getInstance().getRecognizeEngine();
        engine.stopListening();
        engine.setParameter(SDKConstant.Parameter.PARAMERER_AI_ON_OFF, "off");
        engine.setCloudResultListener(new OnCloudResultListener() {
            @Override
            public void onResult(int i, String s) {
                Log.d(TAG, "onASRResult() called with: i = [" + i + "], s = [" + s + "]");
                Gson gson = new Gson();
                VoiceAnswer voiceAnswer = gson.fromJson(s, VoiceAnswer.class);
                //回执
                result.success(voiceAnswer.text);
                IRooboRecognizeEngine engine = VUISDK.getInstance().getRecognizeEngine();
                engine.stopListening();
            }

            @Override
            public void onError(SDKError sdkError) {
                Log.d(TAG, "onError() called with: sdkError = [" + sdkError + "]");
            }
        });
        engine.setOnVadListener(new OnVADListener() {
            @Override
            public void onBeginOfSpeech() {
                Log.d(TAG, "onBeginOfSpeech() called");
            }

            @Override
            public void onEndOfSpeech() {
                Log.d(TAG, "onEndOfSpeech() called");
            }

            @Override
            public void onCancelOfSpeech() {
                Log.d(TAG, "onCancelOfSpeech() called");
            }

            @Override
            public void onAudioData(byte[] bytes) {
            }
        });
        engine.startListening();
    }

    public void onReadClick(MethodCall call, final Result result) {
        String qa = call.argument("qa");

        IRooboRecognizeEngine engine = VUISDK.getInstance().getRecognizeEngine();
        engine.stopListening();

        engine.setParameter(SDKConstant.Parameter.PARAMERER_ORAL_TESTING, "on");
        engine.setParameter(SDKConstant.Parameter.PARAMERER_AI_CONTEXTS, "");

        engine.setCloudResultListener(new OnCloudResultListener() {
            @Override
            public void onResult(int i, String s) {
                Log.d(TAG, "onReadResult() called with: i = [" + i + "], s = [" + s + "]");
                Gson gson = new Gson();
                FollowAnswer answer = gson.fromJson(s, FollowAnswer.class);
                result.success(answer.Data.pronunciation + "");
                IRooboRecognizeEngine engine = VUISDK.getInstance().getRecognizeEngine();
                engine.stopListening();
            }

            @Override
            public void onError(SDKError sdkError) {
                Log.d(TAG, "onError() called with: sdkError = [" + sdkError + "]");
            }
        });
        engine.setOnVadListener(new OnVADListener() {
            @Override
            public void onBeginOfSpeech() {
                Log.d(TAG, "onBeginOfSpeech() called");
            }

            @Override
            public void onEndOfSpeech() {
                Log.d(TAG, "onEndOfSpeech() called");
            }

            @Override
            public void onCancelOfSpeech() {
                Log.d(TAG, "onCancelOfSpeech() called");
            }

            @Override
            public void onAudioData(byte[] bytes) {
            }
        });
        engine.setParameter(
                SDKConstant.Parameter.PARAMERER_ORAL_TESTING_EX,
                JsonUtil.toJsonString(new RequestReadScore(1, qa)));
        engine.startListening();
    }


    private static void init(Context context, String sn, String publicKey, final Result result) {
        if (VUISDK.getInstance().hasInited()) {
            Log.e(TAG, "init: has inited");
            result.success("succeed");
            return;
        }

        SDKRequiredInfo info = new SDKRequiredInfo();
        info.setDeviceID(sn);
        info.setAgentID("xxxxxxxxxxxxxxxxxx");
        info.setPublicKey(publicKey);
        info.setAgentToken("xxxxxxxxxxxxxxxxxxxxxxxxx");

        ISDKSettings settings = VUISDK.getInstance().getSettings();
        settings.setTokenType(AIParamInfo.TOKEN_MODE_INNER);
        settings.setEnv(SDKConstant.EnvType.ENV_TEST);
        settings.setLogLevel(SDKConstant.LogLevelType.LOG_LEVEL_VERBOSE);
        VUISDK.getInstance().init(context, info, new ISDKInitListener() {
            @Override
            public void onSuccess() {
                Log.d(TAG, "onSuccess() called");
                IRooboRecognizeEngine engine = VUISDK.getInstance().getRecognizeEngine();
                engine.setEngineEnable(SDKConstant.Engine.ENGINE_LOCAL_REC, false);
                engine.setEngineEnable(SDKConstant.Engine.ENGINE_VAD, false);
                engine.setEngineEnable(SDKConstant.Engine.ENGINE_WAKEUP, false);
            }

            @Override
            public void onFailed(SDKError sdkError) {
                Log.d(TAG, "onFailed() called with: sdkError = [" + sdkError + "]");
            }
        });
        result.success("succeed");
    }

}

step2.3 实现iOS API

和android 一样 实现一套ios平台代码

step2.4 flutter 调用

在pubspec.yaml中添加依赖

dependencies:
  flutter:
    sdk: flutter

  # The following adds the Cupertino Icons font to your application.
  # Use with the CupertinoIcons class for iOS style icons.
  cupertino_icons: ^0.1.2
  dio: ^3.0.0
  shared_preferences: ^0.5.4+6
  permission_handler: ^4.0.0

  voice_plugin:
    path: voice_plugin

//导包
  import 'package:voice_plugin/voice_plugin.dart';

  Future<String> getRead(String qa) async {
    return await VoicePlugin.getRead(qa);
  }

  Future<String> getASR() async {
    return await VoicePlugin.getASR;
  }
 //调用
 getRead(msg.extra.question)
 .then((str) {
    NetHelper.post(
        action: msg.action,
        session: msg.session,
        answer: str,
        hostId: msg.hostId);
    Navigator.pop(context);
  });
 
  getASR().then((str) {
    NetHelper.post(
        action: msg.action,
        session: msg.session,
        answer: str,
        hostId: msg.hostId);
    Navigator.pop(context);
  });

Flutter调用原生并传递数据

static Future register(String sn, String publicKey) async {
    await _channel.invokeMethod('register', {"sn": sn, "publicKey": publicKey});
  }

我们将传进来的参数重新组装成了Map并传递给了invokeMethod。其中invokeMethod函数第一个参数为函数名称，即register，我们将在原生平台用到这个名字。第二个参数为要传递给原生的数据。我们看一下invokeMethod的源码：

  @optionalTypeArgs
  Future<T> invokeMethod<T>(String method, [ dynamic arguments ]) async {
    assert(method != null);
    final ByteData result = await binaryMessenger.send(
      name,
      codec.encodeMethodCall(MethodCall(method, arguments)),
    );
    if (result == null) {
      throw MissingPluginException('No implementation found for method $method on channel $name');
    }
    final T typedResult = codec.decodeEnvelope(result);
    return typedResult;
  }

第二个参数是dynamic的，那么我们是否可以传递任何数据类型呢？至少语法上是没有错误的，但实际上这是不允许的，只有对应平台的codec支持的类型才能进行传递，也就是上文提到的数据类型对应表，这条规则同样适用于返回值，也就是原生给Flutter传值。请记住这条规定

在平台接收Flutter传递过来的数据

	@Override
    public void onMethodCall(MethodCall call, Result result) {
        switch (call.method) {
            case "getPlatformVersion":
                result.success("Android " + android.os.Build.VERSION.RELEASE);
                break;
            case "register":
                registerAndInit(call, result);
                break;
            case "getASR":
                onASRClick(result);
                break;
            case "getRead":
                onReadClick(call, result);
                break;
            default:
                result.notImplemented();
                break;
        }
    }

call.method是方法名称，我们要通过方法名称比对完成调用匹配。当call.method == "register"成立时，说明我们要调用register，从而进行更多的操作。
如发现call.method不存在,通过result向Flutter报告一下该方法没实现：result.notImplemented()当调用这个方法之后，我们会在Flutter层收到一个没实现该方法的异常。
iOS端也是大同小异：

- (void)handleMethodCall:(FlutterMethodCall *)call result:(FlutterResult)result {
    if ([@"registerApp" isEqualToString:call.method]) {
        [_fluwxWXApiHandler registerApp:call result:result];
        return;
    }
}

如果方法不存在：result(FlutterMethodNotImplemented);

其数据放在call.arguments，其类型为java.lang.Object，与Flutter传递过来数据类型一一对应。如果数据类型是Map，我们可以通过以下方式取出对应值：

String sn = call.argument("sn");
String publicKey = call.argument("publicKey");

IOS也一样

NSString *appId = call.arguments[@"sn"];
NSString *appId = call.arguments[@"publicKey"];

从平台回调结果给Flutter

在接收Flutter调用的时候会传递一个名字result的参数，通过result我们可以向Flutter回值有三种形式：
success，成功
error,遇到错误
notImplemented,没实现对应方法

result.success("succeed")
result.error("invalid sn", "are you sure your sn is correct ?", sn)

result("succeed");
result([FlutterError errorWithCode:@"invalid sn" message:@"are you sure your sn is correct ? " details:sn]);

平台如何调用Flutter

如果插件的功能很重，或者是异步回调，此时我们就不好使用Result 对象回传结果，比如微信分享，当我们完成分享时，我们可能将分享结果传回Flutter。微信的这些回调是异步的，

原理也一样，在原生代码中，我们也有一个MethodChannel：

val channel = MethodChannel(registrar.messenger(), "xxx")

let channel = FlutterMethodChannel(name: "xxx", binaryMessenger: registrar.messenger())

当我们拿到了MethodChannel，

      val result = mapOf(
                errStr to response.errStr,
                WechatPluginKeys.TRANSACTION to response.transaction,
                type to response.type,
                errCode to response.errCode,
                openId to response.openId,
                WechatPluginKeys.PLATFORM to WechatPluginKeys.ANDROID
        )

    channel?.invokeMethod("onShareResponse", result)

        NSDictionary *result = @{
                description: messageResp.description == nil ?@"":messageResp.description,
                errStr: messageResp.errStr == nil ? @"":messageResp.errStr,
                errCode: @(messageResp.errCode),
                type: messageResp.type == nil ? @2 :@(messageResp.type),
                country: messageResp.country== nil ? @"":messageResp.country,
                lang: messageResp.lang  == nil ? @"":messageResp.lang,
                fluwxKeyPlatform: fluwxKeyIOS
        };
        [methodChannel invokeMethod:@"onShareResponse" arguments:result];

原生调用Flutter和Flutter调用原生的方式其实是一样的，都是通过MethodChannel调用指定名称的方法，并传递数据。

Flutter的接受原生调用的方式和原生接收Flutter调用的方式应该也是样的：

final MethodChannel _channel = const MethodChannel('XXX')
  ..setMethodCallHandler(_handler);

Future<dynamic> _handler(MethodCall methodCall) {
  if ("onShareResponse" == methodCall.method) {
    _responseController.add(WeChatResponse(methodCall.arguments, WeChatResponseType.SHARE));
  } 
  return Future.value(true);
}

稍微不一样的地方就是，在Flutter中，我们使用到了Stream:

StreamController<WeChatResponse> _responseController =
    new StreamController.broadcast();
 Stream<WeChatResponse> get response => _responseController.stream;

当然了不使用Stream也可以。通过Stream，我们可以更轻松地监听回调数据变化：

response.listen((data) {
  //do work
});