Flutter与原生通信的一切

简介

Flutter与原生之间的通信依赖灵活的消息传递方式：

• 应用的Flutter部分通过平台通道（platform channel）将消息发送到其应用程序的所在的宿主（iOS或Android）应用（原生应用）。

• 宿主监听平台通道，并接收该消息。然后它会调用该平台的API，并将响应发送回客户端，即应用程序的Flutter部分。

1. MethodChannel  // Flutter与原生方法相互调用，用于方法掉用

2. BasicMessageChannel // Flutter与原生相互发送消息，用于数据传递

3. EventChannel // 原生发送消息，Flutter接收，用于数据流通信

可以传递的数据结构

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:
int, if 64 bits not enough	Java.lang.BigInteger	FlutterStandardBigInteger
double	Java.lang.Double	NSNumber numberWithDouble
String	java.lang.String	NSString
Unit8List	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

MethodChannel（互相调用方法）

Android调用Flutter方法：

Android:

1. 初始化MethodChannel

//初始化，传递1. flutterView（MainActivity中getFlutter获取），2. name常量，Flutter中使用同名常量	
MethodChannel methodChannel = new MethodChannel(flutterView, “testflutter”);

2. 调用Flutter方法

通过MethodChannel调用invokeMethod("方法名","传递参数",[Flutter返回参数回调，非必须]);

Flutter:

1. 初始化MethodChannel

static const methodChannel = const MethodChannel('testflutter');

复制代码

2. 添加处理方法到MethodChannel

methodChannel.setMethodCallHandler(_addNativeMethod);

3. 处理android调用的方法，根据方法名

Flutter调用Android方法：

Android：

1. 初始化MethodChannel，并添加自定义plugin

MethodChannel methodChannel = new MethodChannel(flutterView, METHOD_CHANNEL);	
methodChannel.setMethodCallHandler(plugin);

2. 自定义的plugin实现MethodChannel.MethodCallHandler接口的onMethodCall方法

@Override	
public void onMethodCall(MethodCall methodCall, MethodChannel.Result result) {	
  // Flutter调用Native的方法	
  if (methodCall.method.equals("getBatteryLevel")) {	
    int batteryLevel = getBatteryLevel();	
    if (batteryLevel != -1) {	
      result.success(batteryLevel);	
    } else {	
      result.error("UNAVALIABLE", "battery level unavaliable", null);	
    }	
  } else {	
    result.notImplemented();	
  }	
}	
//在onMethodCall中监听Flutter调用什么名字的方法（此处getBatterLevel），通过result返回方法的执行结果。

Flutter：

1. 初始化MethodChannel

static const methodChannel = const MethodChannel('testflutter');

复制代码

2. 调用Android的方法，接收返回数据

//方法通道的方法是异步的	
Future _getBatteryLevel() async {	
  String batteryLevel;	
  try {	
    final int result = await methodChannel.invokeMethod('getBatteryLevel');	
    batteryLevel = 'Battery level $result .';	
  } on PlatformException catch (e) {	
    batteryLevel = 'Battery level unknown ${e.message}';	
  }	
  setState(() {	
    _batteryLevel = batteryLevel;	
  });	
}

BasicMessageChannel（互相发送消息）

Android给Flutter发消息：

Android：

1. 初始化BasicMethodChannel

	
BasicMessageChannel messageChannel =	
 new BasicMessageChannel<>(flutterView, 	
"messageChannel", StandardMessageCodec.INSTANCE);	
	
复制代码

2. 调用发送消息的方法

private void sendMessageToFlutter() {	
  if (this.mBasicMessageChannel != null) {	
    this.mBasicMessageChannel.send("Message From Native");	
  }	
}	

Flutter：

1. 初始化BasicMessageChannel

static const basicMessageChannel = BasicMessageChannel('messageChannel', StandardMessageCodec());
复制代码

2. 添加接收信息处理方法

void _listenMessageFromNative() {	
  basicMessageChannel.setMessageHandler(_receiveMessageFromNative);	
}

3. 处理接收的数据

//Flutter接收Native发来的消息	
Future _receiveMessageFromNative(Object result) async {	
  setState(() {	
    _messageFromNative = result.toString();	
  });	
}	

Flutter给Android发消息：

Android：

1. 初始化BasicMessageChannel并添加plugin给handler

BasicMessageChannel messageChannel = new BasicMessageChannel<>(flutterView, "messageChannel", StandardMessageCodec.INSTANCE);	
messageChannel.setMessageHandler(plugin);

2. plugin实现BasicMessageChannel.MessageHandler接口的onMessage方法，处理接收到的信息

@Override	
public void onMessage(Object o, BasicMessageChannel.Reply reply) {	
  Toast.makeText(mContext, o.toString(), Toast.LENGTH_LONG).show();	
  reply.reply(o.toString()+" back from native");	
}	
//reply返回数据给Flutter

Flutter：

1. 初始化BasicMessageChannel

static const basicMessageChannel = 	
BasicMessageChannel('messageChannel', StandardMessageCodec());

2. 发送消息给Android并接收返回数据

EventChannel（原生发送消息，Flutter接收）

Android：

1. 初始化EventChannel并添加plugin给handler

EventChannel eventChannel = new EventChannel(flutterView, EVENT_CHANNEL);	
eventChannel.setStreamHandler(plugin);

2. plugin实现EventChannel.StreamHandler接口及onListen、onCancel方法

3. 在onListen中通过EventChannel.EventShink的实例发消息给Flutter

@Override	
public void onListen(Object o, EventChannel.EventSink eventSink) {	
  BroadcastReceiver chargingBroadcastReceiver = createChargingBroadcaseReceiver(eventSink);	
  mContext.registerReceiver(chargingBroadcastReceiver,new IntentFilter(Intent.ACTION_BATTERY_CHANGED));	
}	
@Override	
public void onCancel(Object o) {	
}	
private BroadcastReceiver createChargingBroadcaseReceiver(EventChannel.EventSink eventSink) {	
  return new BroadcastReceiver() {	
    @Override	
    public void onReceive(Context context, Intent intent) {	
      int status = intent.getIntExtra(BatteryManager.EXTRA_STATUS, -1);	
      if (status == BatteryManager.BATTERY_STATUS_UNKNOWN) {	
        eventSink.error("UNAVALIABLE", "charging status is unavailable", null);	
      } else {	
        boolean isCharging = status == BatteryManager.BATTERY_STATUS_CHARGING;	
        eventSink.success(isCharging ? "charging" : "disCharging");	
      }	
    }	
  };	
}

Flutter:

1. 初始化EventChannel

static const _eventChannel = const EventChannel('charging');

2. 添加接收数据方法

void listenNativeEvent() {	
  _eventChannel.receiveBroadcastStream().listen(_onEvent, onError: _onError);	
}	
//接收返回的数据	
void _onEvent(Object object) {	
  String s = "Battery is ${object == 'charging' ? '' : 'dis'}Charging";	
  setState(() {	
    _batteryStatus = s;	
  });	
}

桥接View给Flutter使用

Android：

1. 自定义View，继承自PlatformView

2. 实现PlatformViewFactory

public class TextViewFactory extends PlatformViewFactory {	
  private MessageCodec