前言

我们都知道Flutter开发的app是可以同时在iOS和Android系统上运行的。显然Flutter需要有和Native通信的能力。在实际项目中，Flutter并不能全面满足项目需求，比如获取一些硬件信息（如电池电量），这些都是一些比较简单的Native需求，Flutter官方也给出了一些比较常用的Plugin。但在实际项目中可能需求就没那么简单了，比如融云通讯、环信通讯，再或者项目自定义的需求，这可能就需要我们自己去写插件了。这里我就以Flutter获取Native电池电量和电池状态（充电中、充满电、未充电）为例（包括IOS-Swift 和 Android-Kotlin）来实现自己的需求。

思路

Flutter是如何做到的呢？当然是Flutter官方给的Platform Channels。如图：

上图来自Flutter官网，表明了Platform Channels的架构示意图。Platform Channel包括MethodChannel、EventChannel和BasicMessageChannel三大通道。

Platform Channel 支持的数据类型

比较常用

MethodChannel

俗称方法通道（个人见解）用于传递方法调用

以 Flutter 获取 手机电量为例, 在 Flutter 界面中要想获取 Android/iOS 的电量, 首先要在 Native 编写获取电量的功能, 供 Flutter 来调用。

• Native - iOS

public class SwiftFlutterPluginLearningPlugin: NSObject, FlutterPlugin {public static func register(with registrar: FlutterPluginRegistrar) {let instance = SwiftFlutterPluginLearningPlugin()let methodChannel = FlutterMethodChannel(name: "plugins.limit.io/battery", binaryMessenger: registrar.messenger())//注册电池（plugins.limit.io/battery）方法通道registrar.addMethodCallDelegate(instance, channel: methodChannel)}public func handle(_ call: FlutterMethodCall, result: @escaping FlutterResult) {switch call.method {case "getBatteryLevel":let batterLevel = getBatteryLevel()if(batterLevel == -1) {result(FlutterError(code: "UNAVAILABLE", message: "Battery info unavailable", details: nil));} else {result(batterLevel)}default:result(FlutterMethodNotImplemented)}}//获取电池电量private func getBatteryLevel() -> Float {let device = UIDevice.currentdevice.isBatteryMonitoringEnabled = trueif device.batteryState == .unknown {return -1;} else {return UIDevice.current.batteryLevel}}
}复制代码

• Native - Android

public class FlutterPluginLearningPlugin : FlutterPlugin, MethodCallHandler, EventChannel.StreamHandler {private var applicationContext: Context? = null/*** 方法通道*/private var methodChannel: MethodChannel? = null/*** 连接到引擎*/override fun onAttachedToEngine(@NonNull flutterPluginBinding: FlutterPlugin.FlutterPluginBinding) {onAttachedToEngine(flutterPluginBinding.applicationContext, flutterPluginBinding.binaryMessenger)}private fun onAttachedToEngine(applicationContext: Context, messenger: BinaryMessenger) {this.applicationContext = applicationContextmethodChannel = MethodChannel(messenger, "plugins.limit.io/battery")methodChannel?.setMethodCallHandler(this)}companion object {@JvmStaticfun registerWith(registrar: Registrar) {val instance = FlutterPluginLearningPlugin()instance.onAttachedToEngine(registrar.context(), registrar.messenger())}}/*** 回调方法*/override fun onMethodCall(@NonNull call: MethodCall, @NonNull result: Result) {if (call.method == "getBatteryLevel") {val batterLevel = getBatteryLevel()if (batterLevel != -1) {result.success(batterLevel)} else {result.error("UNAVAILABLE", "Battery level not available.", null);}} else {result.notImplemented()}}/*** 从引擎中脱离*/override fun onDetachedFromEngine(@NonNull binding: FlutterPlugin.FlutterPluginBinding) {applicationContext = nullmethodChannel?.setMethodCallHandler(null)methodChannel = null}/*** 获取电池电量方法*/private fun getBatteryLevel(): Int {var batteryLevel = -1batteryLevel = if (VERSION.SDK_INT >= VERSION_CODES.LOLLIPOP) {val batteryManager = applicationContext?.let { getSystemService(it, BatteryManager::class.java) }batteryManager!!.getIntProperty(BatteryManager.BATTERY_PROPERTY_CAPACITY)} else {val intent = ContextWrapper(applicationContext).registerReceiver(null, IntentFilter(Intent.ACTION_BATTERY_CHANGED))intent.getIntExtra(BatteryManager.EXTRA_LEVEL, -1) * 100 / intent.getIntExtra(BatteryManager.EXTRA_SCALE, -1)}return batteryLevel}
}
复制代码

• Flutter

flutter 插件

class FlutterPluginLearning {factory FlutterPluginLearning() {if (_instance == null) {final MethodChannel methodChannel =const MethodChannel('plugins.limit.io/battery');_instance = FlutterPluginLearning.init(methodChannel);}return _instance;}FlutterPluginLearning.init(this._methodChannel);static FlutterPluginLearning _instance;final MethodChannel _methodChannel;Future<int> get batteryLevel => _methodChannel.invokeMethod<int>('getBatteryLevel').then<int>((dynamic result) => result);
}复制代码

flutter 调用

FlutterPluginLearning _battery = FlutterPluginLearning();
_battery.batteryLevel.then((int batteryLevel) {//to do something you want
});
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EventChannel

俗称流通道（个人见解）用于数据流（event streams）的通信 以 Flutter 获取 手机电池状态为例, 在 Flutter 界面中要想获取 Android/iOS 的电池状态, 首先要在 Native 编写获取电池状态的功能, 供 Flutter 来调用。

• Native - iOS

public class SwiftFlutterPluginLearningPlugin: NSObject, FlutterPlugin, FlutterStreamHandler {var eventSink: FlutterEventSink?public static func register(with registrar: FlutterPluginRegistrar) {let instance = SwiftFlutterPluginLearningPlugin()let evenChannel = FlutterEventChannel(name: "plugins.limit.io/charging", binaryMessenger: registrar.messenger())evenChannel.setStreamHandler(instance)}public func handle(_ call: FlutterMethodCall, result: @escaping FlutterResult) {}public func onListen(withArguments arguments: Any?, eventSink events: @escaping FlutterEventSink) -> FlutterError? {eventSink = eventsUIDevice.current.isBatteryMonitoringEnabled = trueself.sendBatteryStateEvent()NotificationCenter.default.addObserver(self, selector: #selector(onBatteryStateDidChange(notification:)), name: UIDevice.batteryStateDidChangeNotification, object: nil)return nil}public func onCancel(withArguments arguments: Any?) -> FlutterError? {NotificationCenter.default.removeObserver(self)eventSink = nilreturn nil}@objc private func onBatteryStateDidChange(notification: NSNotification?) {self.sendBatteryStateEvent()}private func sendBatteryStateEvent() {if eventSink == nil {return}let state = UIDevice.current.batteryStateswitch state {case .full:eventSink!("full")breakcase .charging:eventSink!("charging")breakcase .unplugged:eventSink!("unplugged")breakdefault:eventSink!(FlutterError(code: "UNAVAILABLE", message: "Charging status unavailable", details: nil))break}}
}复制代码

• Native - Android

public class FlutterPluginLearningPlugin : FlutterPlugin, MethodCallHandler, EventChannel.StreamHandler {private var applicationContext: Context? = null/*** 事件流通道* Native 需要频繁的发送消息给 Flutter, 比如监听网络状态, 蓝牙设备等等然后发送给 Flutter*/private var eventChannel: EventChannel?= nullprivate var chargingStateChangeReceiver: BroadcastReceiver? = null/*** 连接到引擎*/override fun onAttachedToEngine(@NonNull flutterPluginBinding: FlutterPlugin.FlutterPluginBinding) {onAttachedToEngine(flutterPluginBinding.applicationContext, flutterPluginBinding.binaryMessenger)}private fun onAttachedToEngine(applicationContext: Context, messenger: BinaryMessenger) {this.applicationContext = applicationContexteventChannel = EventChannel(messenger, "plugins.limit.io/charging")eventChannel?.setStreamHandler(this)}companion object {@JvmStaticfun registerWith(registrar: Registrar) {val instance = FlutterPluginLearningPlugin()instance.onAttachedToEngine(registrar.context(), registrar.messenger())}}/*** 回调方法*/override fun onMethodCall(@NonNull call: MethodCall, @NonNull result: Result) {}/*** 从引擎中脱离*/override fun onDetachedFromEngine(@NonNull binding: FlutterPlugin.FlutterPluginBinding) {applicationContext = nulleventChannel?.setStreamHandler(null)eventChannel = null}/*** 监听*/override fun onListen(arguments: Any?, events: EventChannel.EventSink?) {chargingStateChangeReceiver = createChargingStateChangeReceiver(events)applicationContext?.registerReceiver(chargingStateChangeReceiver, IntentFilter(Intent.ACTION_BATTERY_CHANGED))}/*** 取消监听*/override fun onCancel(arguments: Any?) {applicationContext?.unregisterReceiver(chargingStateChangeReceiver)chargingStateChangeReceiver = null}private fun createChargingStateChangeReceiver(events: EventChannel.EventSink?): BroadcastReceiver {return object : BroadcastReceiver() {override fun onReceive(context: Context?, intent: Intent?) {when (intent?.getIntExtra(BatteryManager.EXTRA_STATUS, -1)) {BatteryManager.BATTERY_STATUS_CHARGING -> events?.success("charging")BatteryManager.BATTERY_STATUS_FULL -> events?.success("full")BatteryManager.BATTERY_STATUS_DISCHARGING -> events?.success("discharging")else -> events?.error("UNAVAILABLE", "Charging status unavailable", null)}}}}}复制代码

• Flutter

flutter 插件

enum BatteryState {/// The battery is completely full of energy.full,/// The battery is currently storing energy.charging,/// The battery is currently losing energy.discharging
}class FlutterPluginLearning {factory FlutterPluginLearning() {if (_instance == null) {final EventChannel eventChannel =const EventChannel('plugins.limit.io/charging');_instance = FlutterPluginLearning.init(eventChannel);}return _instance;}FlutterPluginLearning.init(this._eventChannel);static FlutterPluginLearning _instance;final EventChannel _eventChannel;Stream<BatteryState> _onBatteryStateChanged;Stream<BatteryState> get onBatteryStateChanged {if (_onBatteryStateChanged == null) {_onBatteryStateChanged = _eventChannel.receiveBroadcastStream().map((dynamic event) => _parseBatteryState(event));}return _onBatteryStateChanged;}BatteryState _parseBatteryState(String state) {switch (state) {case 'full':return BatteryState.full;case 'charging':return BatteryState.charging;case 'discharging':return BatteryState.discharging;default:throw ArgumentError('$state is not a valid BatteryState.');}}
}
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flutter 调用

FlutterPluginLearning _battery = FlutterPluginLearning();
StreamSubscription<BatteryState> _batteryStateSubscription;
_batteryStateSubscription =_battery.onBatteryStateChanged.listen((BatteryState state) {String batteryState = 'UnKnow';switch (state) {case BatteryState.full:batteryState = '已充满';break;case BatteryState.charging:batteryState = '充电中';break;case BatteryState.discharging:batteryState = '未充电';break;default:}// do something you want});
复制代码

BasicMessageChannel

俗称消息直接通道（个人见解）用于传递字符串和半结构化的信息。 如果仅仅是简单的通信而不是调用某个方法或者是事件流, 可以使用 BasicMessageChannel。BasicMessageChannel 也可以实现 Flutter 和 Native 的双向通信, 下面的示例图就是官方的例子:

详细查看（八）Flutter 和 Native之间的通信详解 的 BasicMessageChannel

Reference

（八）Flutter 和 Native之间的通信详解

官网 - platform-channels

源码

github.com/TBoyLi/flut… 觉得ok! Star ✨✨✨✨✨✨

作者：redli
链接：https://juejin.im/post/5ea78e2be51d454dc93dd94a
来源：掘金
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