Flutter中调用原生-platform channels(平台通道)

上一次介绍过Flutter中调用原生相册/相机功能,这个是因为flutter官网提供了三方的ImagePicker插件,可以快速实现访问相机功能,但是,如果像某些原生的信息,没有很好的插件,我们只能通过platform channels(平台通道)来获取信息。
以一个Flutter中文网的显示电池电量的例子,来介绍下MethodChannel来实现客户端(UI)和宿主(平台)之间的信息传递。
platform channels(平台通道)

使用平台通道在客户端(Flutter UI)和宿主(iOS平台 & Android平台)之间传递消息,如下图所示(Flutter中文网提供):

Flutter中调用原生-platform channels(平台通道)_第1张图片
001.png

消息和响应是异步传递的,以确保用户界面保持响应(不会挂起)。

调用过程大致如下:
1.在客户端,MethodChannel (API)可以发送与方法调用相对应的消息;
2.平台端(iOS、Android端)接收方法,并返回结果;
iOS端通过FlutterMethodChannel做出响应;
Android端通过MethodChannel做出响应;

Flutter中调用原生-platform channels(平台通道)_第2张图片
002.png

实战过程:

我们这里创建一个获取电池电量信息的项目,分别通过iOS和Android原生代码来获取对应的信息:

1.Step 1: 创建一个新的Flutter应用程序项目
① 首先创建一个新的Flutter应用程序:

在终端运行中:flutter create batterylevel
目前默认创建的Flutter项目,对应iOS的编程语言是Swift,对应Android的编程语言是kotlin

如果我们希望指定编程语言,比如iOS编程语言为Objective-C,Android的编程语言为Java
flutter create -i objc -a java batterylevel2

② 使用Android studio打开创建的项目,Flutter端获取当前电量信息代码如下

class _MyHomePageState extends State {
  int _level = 0;
  static const platform = const MethodChannel("flutter.com/battery");

  @override
  Widget build(BuildContext context) {

    return Scaffold(
      appBar: AppBar(
        title: Text(widget.title),
      ),
      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: [
            Text(
              '剩余电量:',
            ),
            Text(
              '$_level',
              style: Theme.of(context).textTheme.headline4,
            ),
            RaisedButton(
              child: Text("获取剩余电量"),
              onPressed: _getBatteryInfo,
            ),
          ],
        ),
      ), // This trailing comma makes auto-formatting nicer for build methods.
    );
  }

  /// 获取电量信息
  void _getBatteryInfo() async {
    final result = await platform.invokeMethod("flutter.com/battery");
    setState(() {
      _level = result;
    });
  }

}

Step 2: 打开batterylevel下的iOS的Runner工程,

Flutter中调用原生-platform channels(平台通道)_第3张图片
003.png

iOS端对应的获取电量信息的代码如下:

@objc class AppDelegate: FlutterAppDelegate {
  override func application(
    _ application: UIApplication,
    didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey: Any]?
  ) -> Bool {
    
    // 实现获取电池信息的功能
    // 1.获取FlutterViewController
    let controller: FlutterViewController = window.rootViewController as! FlutterViewController ;
    // 2.创建FlutterMethodChannel
    let channel = FlutterMethodChannel(name: "flutter.com/battery", binaryMessenger: controller.binaryMessenger);
    // 3.监听channel调用方法(Flutter中platform.invokeMethod方法调用,下面这个函数回调就会执行)
    channel.setMethodCallHandler { (call:FlutterMethodCall,result: @escaping FlutterResult) in
        //3.1 判断当前方法是否是getBatteryInfo
        guard call.method == "getBatteryInfo" else {
            result(FlutterMethodNotImplemented);
            return;
        }
        //3.2获取电池信息
        let device = UIDevice.current;
        device.isBatteryMonitoringEnabled = true;
        
        //3.3获取电量信息
        if device.batteryState == UIDevice.BatteryState.unknown {
            result(FlutterError(code:"unknow", message:"batter info is unknow",details:nil));
            // result(1000);
        } else {
            result(Int(device.batteryLevel * 100));
        }
    };
    
    GeneratedPluginRegistrant.register(with: self)
    return super.application(application, didFinishLaunchingWithOptions: launchOptions)
    
  }
}

Step 3: 打开batterylevel下的android的工程

Flutter中调用原生-platform channels(平台通道)_第4张图片
004.png

android端对应的获取电量信息的代码如下(kotlin):

class MainActivity: FlutterActivity() {

    private val channel = "flutter.com/battery"

    override fun configureFlutterEngine(@NonNull flutterEngine: FlutterEngine) {
        GeneratedPluginRegistrant.registerWith(flutterEngine);

        // 1.创建MethodChannel对象
        val methodChannel = MethodChannel(flutterEngine.dartExecutor.binaryMessenger, channel)

        // 2.添加调用方法的回调
        methodChannel.setMethodCallHandler {
            // Note: this method is invoked on the main thread.
            call, result ->
            // 2.1.如果调用的方法是getBatteryInfo,那么正常执行
            if (call.method == "getBatteryInfo") {
                // 2.1.1.调用另外一个自定义方法回去电量信息
                val batteryLevel = getBatteryLevel()

                // 2.1.2. 判断是否正常获取到
                if (batteryLevel != -1) {
                    // 获取到返回结果
                    result.success(batteryLevel)
                } else {
                    // 获取不到抛出异常
                    result.error("UNAVAILABLE", "Battery level not available.", null)
                }
            } else {
                // 2.2.如果调用的方法是getBatteryInfo,那么正常执行
                result.notImplemented()
            }
        }
    }

    private fun getBatteryLevel(): Int {
        val batteryLevel: Int
        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.LOLLIPOP) {
            val batteryManager = getSystemService(Context.BATTERY_SERVICE) as BatteryManager
            batteryLevel = batteryManager.getIntProperty(BatteryManager.BATTERY_PROPERTY_CAPACITY)
        } else {
            val intent = ContextWrapper(applicationContext).registerReceiver(null, IntentFilter(Intent.ACTION_BATTERY_CHANGED))
            batteryLevel = intent!!.getIntExtra(BatteryManager.EXTRA_LEVEL, -1) * 100 / intent.getIntExtra(BatteryManager.EXTRA_SCALE, -1)
        }
        return batteryLevel
    }
}

andriod运行效果如下:

Flutter中调用原生-platform channels(平台通道)_第5张图片
005.jpg

至此,Flutter中和原生的通信暂时学习记录至此,后续有有新的用法将持续更新。
DEMO下载.

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