原生Android与Flutter通信方式(二)

96
aimaile
2019.04.21 18:36 字数 651

MethodChannel用法

Native端:

构造方法原型

//会构造一个StandardMethodCodec.INSTANCE类型的MethodCodec
MethodChannel(BinaryMessenger messenger, String name)
//或
MethodChannel(BinaryMessenger messenger, String name, MethodCodec codec)

  • BinaryMessenger messenger - 消息信使,是消息的发送与接收的工具;
  • String name - Channel的名字,也是其唯一标识符;
  • MethodCodec codec - 用作MethodChannel的编解码器;

setMethodCallHandler方法原型

setMethodCallHandler(@Nullable MethodChannel.MethodCallHandler handler) 

  • @Nullable MethodChannel.MethodCallHandler handler - 消息处理器,配合BinaryMessenger完成消息的处理;

在创建好MethodChannel后,需要调用它的setMessageHandler方法为其设置一个消息处理器,以便能加收来自Dart的消息。

MethodChannel.MethodCallHandler原型

public interface MethodCallHandler {
    void onMethodCall(MethodCall var1, MethodChannel.Result var2);
}

  • onMethodCall(MethodCall call, MethodChannel.Result result) - 用于接受消息,call是消息内容,它有两个成员变量String类型的call.method表示调用的方法名,Object 类型的call.arguments表示调用方法所传递的入参;MethodChannel.Result result是回复此消息的回调函数提供了result.successresult.errorresult.notImplemented方法调用;
public class MethodChannelPlugin implements MethodCallHandler {
    private final Activity activity;

    /**
     * Plugin registration.
     */
    public static void registerWith(FlutterView flutterView) {
        MethodChannel channel = new MethodChannel(flutterView, "MethodChannelPlugin");
        MethodChannelPlugin instance = new MethodChannelPlugin((Activity) flutterView.getContext());
        channel.setMethodCallHandler(instance);
    }

    private MethodChannelPlugin(Activity activity) {
        this.activity = activity;
    }

    @Override
    public void onMethodCall(MethodCall call, Result result) {
        switch (call.method) {//处理来自Dart的方法调用
            case "showMessage":
                showMessage(call.arguments());
                result.success("MethodChannelPlugin收到:" + call.arguments);//返回结果给Dart
                break;
            default:
                result.notImplemented();
        }
    }

    /**
     * 展示来自Dart的数据
     *
     * @param arguments
     */
    private void showMessage(String arguments) {
        if (activity instanceof IShowMessage) {
            ((IShowMessage) activity).onShowMessage(arguments);
        }
        Toast.makeText(activity, arguments, Toast.LENGTH_SHORT).show();
    }
}

Dart端:

构造方法原型

const MethodChannel(this.name, [this.codec = const StandardMethodCodec()])
  • String name - Channel的名字,要和Native端保持一致;
  • MethodCodec codec - 消息的编解码器,默认是StandardMethodCodec,要和Native端保持一致;

invokeMethod方法原型

Future<T> invokeMethod<T>(String method, [ dynamic arguments ])

  • String method:要调用Native的方法名;
  • [ dynamic arguments ]:调用Native方法传递的参数,可不传;
import 'package:flutter/services.dart';
...
static const MethodChannel _methodChannelPlugin =
      const MethodChannel('MethodChannelPlugin');
...
String response;
    try {
        response = await _methodChannelPlugin.invokeMethod('send', value);
    } on PlatformException catch (e) {
      print(e);
    }
...

EventChannel用法

Native端:

构造方法原型

//会构造一个StandardMethodCodec.INSTANCE类型的MethodCodec
EventChannel(BinaryMessenger messenger, String name)
//或
EventChannel(BinaryMessenger messenger, String name, MethodCodec codec)

  • BinaryMessenger messenger - 消息信使,是消息的发送与接收的工具;
  • String name - Channel的名字,也是其唯一标识符;
  • MethodCodec codec - 用作EventChannel的编解码器;

setStreamHandler方法原型

void setStreamHandler(EventChannel.StreamHandler handler)

EventChannel.StreamHandler handler - 消息处理器,配合BinaryMessenger完成消息的处理;
在创建好EventChannel后,如果要让其接收Dart发来的消息,则需要调用它的setStreamHandler方法为其设置一个消息处理器。

EventChannel.StreamHandler原型

public interface StreamHandler {
    void onListen(Object args, EventChannel.EventSink eventSink);

    void onCancel(Object o);
}

  • void onListen(Object args, EventChannel.EventSink eventSink) - Flutter Native监听事件时调用,Object args是传递的参数,EventChannel.EventSink eventSink是Native回调Dart时的会回调函数,eventSink提供successerrorendOfStream三个回调方法分别对应事件的不同状态;
  • void onCancel(Object o) - Flutter取消监听时调用;
public class EventChannelPlugin implements EventChannel.StreamHandler {
    private List<EventChannel.EventSink> eventSinks = new ArrayList<>();

    static EventChannelPlugin registerWith(FlutterView flutterView) {
        EventChannelPlugin plugin = new EventChannelPlugin();
        new EventChannel(flutterView, "EventChannelPlugin").setStreamHandler(plugin);
        return plugin;
    }

    void sendEvent(Object params) {
        for (EventChannel.EventSink eventSink : eventSinks) {
            eventSink.success(params);
        }
    }

    @Override
    public void onListen(Object args, EventChannel.EventSink eventSink) {
        eventSinks.add(eventSink);
    }

    @Override
    public void onCancel(Object o) {

    }
}

Dart端:

构造方法原型

const EventChannel(this.name, [this.codec = const StandardMethodCodec()]);
  • String name - Channel的名字,要和Native端保持一致;
  • MethodCodec codec - 消息的编解码器,默认是StandardMethodCodec,要和Native端保持一致;

receiveBroadcastStream方法原型

Stream<dynamic> receiveBroadcastStream([ dynamic arguments ]) 

  • dynamic arguments - 监听事件时向Native传递的数据;

初始化一个广播流用于从channel中接收数据,它返回一个Stream接下来需要调用Stream的listen方法来完成注册,另外需要在页面销毁时调用Stream的cancel方法来取消监听;

import 'package:flutter/services.dart';
...
static const EventChannel _eventChannelPlugin =
      EventChannel('EventChannelPlugin');
StreamSubscription _streamSubscription;
  @override
  void initState() {
    _streamSubscription=_eventChannelPlugin
        .receiveBroadcastStream()
        .listen(_onToDart, onError: _onToDartError);
    super.initState();
  }
  @override
  void dispose() {
    if (_streamSubscription != null) {
      _streamSubscription.cancel();
      _streamSubscription = null;
    }
    super.dispose();
  }
  void _onToDart(message) {
    setState(() {
      showMessage = message;
    }); 
  }
  void _onToDartError(error) {
    print(error);
  }
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