Flutter 实战

一.前置概念

1. Flutter module

概念：

将Flutter添加到你的既有 iOS 应用中(利用CocoaPods)

创建 :

1 2	cd some/path/ flutter create --template module my_flutter

2. 原生插件 (Plugin packages)

概念：

使用 Dart 编写的，按需使用 Java 或 Kotlin、Objective-C 或 Swift 分别在 Android 和/或 iOS 平台实现的 package。

创建 :

1 2	// 使用 -a 选项指定 Android 的语言，或使用 -i 选项指定 iOS 的语言 flutter create --org com.example --template=plugin --platforms=android,ios -a kotlin -i swift flutter_plugins

3. 纯 Dart 库 (Dart packages)

概念：

用 Dart 编写的传统 package，比如 path。其中一些可能包含 Flutter 的特定功能，因此依赖于 Flutter 框架，其使用范围仅限于 Flutter，比如 fluro。

创建：

1	flutter create --template=package flutter_packages

Tips：

你的应用将不能在模拟器上运行 Release 模式，因为 Flutter 还不支持将 Dart 代码编译成 x86/x86_64 ahead-of-time (AOT) 模式的二进制文件。
Flutter.framework 是 Flutter engine 的框架， App.framework 是你的 Dart 代码的编译产物。
参考文档 >>

二. 开始集成

修改Podfile

在 Podfile 中添加下面代码：

1 2	flutter_application_path = '${flutter module目录}' load File.join(flutter_application_path, '.ios', 'Flutter', 'podhelper.rb')

每个需要集成 Flutter 的 Podfile target，执行 install_all_flutter_pods(flutter_application_path)：
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target 'MyApp' do
install_all_flutter_pods(flutter_application_path)
end
运行 pod install。

Tips：

podhelper.rb 脚本会把你的 plugins， Flutter.framework，和 App.framework 集成到你的项目中
运行一个集成flutter module的项目：

cd ${flutter module目录}
flutter pub upgrade
cd ${iOS工程目录}
pod install

三. Flutter Engine

lazy var flutterEngine = FlutterEngine(name: "flutter engine")

  func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey: Any]?) -> Bool {
      // 启动引擎
      self.flutterEngine.run()
      // 注册插件
      GeneratedPluginRegistrant.register(with: self.flutterEngine);
      // 平台视图
      let factory = FLNativeViewFactory(messenger: self.flutterEngine.binaryMessenger)
      self.flutterEngine.registrar(forPlugin: "<plugin-name>")?.register(factory, withId: "<platform-view-type>")
      
      return true
  }

Tips：

1. IDE推荐Android Studio

2.在 FlutterEngine 上调用 run，默认将会调用你的 lib/main.dart 文件里的 main() 函数。

四. Flutter和iOS原生交互

1. Methods Channel

dart To iOS

// 测试 methodChannel  dart -> iOS
MethodChannel methodChannel = const MethodChannel('samples.flutter.dev');
Future<void> _getDeviceInfo() async {
  try {
    final String result = await methodChannel.invokeMethod('getDeviceInfo', {"key": "value"});
    _deviceInfo = result;
    debugPrint(result);
  } on PlatformException catch (e) {
    _deviceInfo = "Failed to get device info: '${e.message}'.";
  }
  setState(() {});
}

// iOS 端
lazy var methodChannel:FlutterMethodChannel = {
    return FlutterMethodChannel(name: "samples.flutter.dev",
                  binaryMessenger: self.flutterEngine.binaryMessenger);
  }()
  
  
func initChannel() {
    self.methodChannel.setMethodCallHandler({
      (call: FlutterMethodCall, result: @escaping FlutterResult) -> Void in
      // Note: this method is invoked on the UI thread.
      // Handle battery messages.
      if (call.method == "getDeviceInfo") {
        let device = UIDevice.current
        result(device.identifierForVendor?.uuidString)
      } else {
        result(FlutterMethodNotImplemented)
      }
    })
  }

iOS To dart

// iOS 端
 self.methodChannel.invokeMethod("callToDart", arguments: ["我是原生端":"呵呵🙂"]) { data in
      // Dart 返回的数据
      if let content = data as? String {
        let alert = UIAlertController(title: "Dart返回的数据", message: content, preferredStyle: UIAlertController.Style.alert)
        alert.addAction(UIAlertAction(title: "确定", style: UIAlertAction.Style.default, handler: { action in
           
        }))
        self.present(alert, animated: true, completion: nil)
      }
    }

// dart 端
MethodChannel methodChannel = const MethodChannel('samples.flutter.dev');

void _listenFromNative() {
  methodChannel.setMethodCallHandler(_fromNative);
}

Future<dynamic> _fromNative(MethodCall call) async {
  if (call.method == "callToDart") {
    debugPrint(call.arguments.toString());
    setState(() {
      _nativeData = call.arguments.toString();
    });
  } else {
    return FlutterError("FlutterMethodNotImplemented");
  }
  return {"FlutterKey": "呵呵🙂"}.toString();
}

2.平台视图托管 (PlatformView)

集成平台视图（后称为平台视图）允许将原生视图嵌入到 Flutter 应用中，所以您可以通过 Dart 将变换、裁剪和不透明度等效果应用到原生视图。（eg: Map,Webview … ）

// Dart 端
Widget build(BuildContext context) {
  // This is used in the platform side to register the view.
  final String viewType = '<platform-view-type>';
  // Pass parameters to the platform side.
  final Map<String, dynamic> creationParams = <String, dynamic>{};

  return UiKitView(
    viewType: viewType,
    layoutDirection: TextDirection.ltr,
    creationParams: creationParams,
    creationParamsCodec: const StandardMessageCodec(),
  );
}

// iOS 端
class FLNativeViewFactory: NSObject, FlutterPlatformViewFactory {
  private var messenger: FlutterBinaryMessenger

  init(messenger: FlutterBinaryMessenger) {
    self.messenger = messenger
    super.init()
  }

  func create(
    withFrame frame: CGRect,
    viewIdentifier viewId: Int64,
    arguments args: Any?
  ) -> FlutterPlatformView {
    return FLNativeView(
      frame: frame,
      viewIdentifier: viewId,
      arguments: args,
      binaryMessenger: messenger)
  }
}

class FLNativeView: NSObject, FlutterPlatformView {
  private var _view: UIView

  init(
    frame: CGRect,
    viewIdentifier viewId: Int64,
    arguments args: Any?,
    binaryMessenger messenger: FlutterBinaryMessenger?
  ) {
    _view = UIView()
    super.init()
    // iOS views can be created here
    createNativeView(view: _view)
  }

  func view() -> UIView {
    return _view
  }

  func createNativeView(view _view: UIView){
    _view.backgroundColor = UIColor.gray
    let nativeLabel = UILabel()
    nativeLabel.text = "Native text from iOS"
    nativeLabel.textColor = UIColor.cyan
    nativeLabel.textAlignment = .center
    nativeLabel.frame = CGRect(x: 0, y: 20, width: 200, height:100)
    _view.addSubview(nativeLabel)
  }
}

// 注册平台视图
  lazy var flutterEngine = FlutterEngine(name: "flutter engine")
  let factory = FLNativeViewFactory(messenger: self.flutterEngine.binaryMessenger)
  self.flutterEngine.registrar(forPlugin: "<plugin-name>")?.register(factory, withId: "<platform-view-type>")

3.Event Channel

// swift
public class EventChannelDemo:NSObject, FlutterStreamHandler{
    
    var channel:FlutterEventChannel?
    var count =  0
    var events:FlutterEventSink?
    
    public override init() {
        super.init()
    }
    
    convenience init(messenger: FlutterBinaryMessenger) {
        self.init()
        channel = FlutterEventChannel(name: "samples.flutter.dev.EventChannel", binaryMessenger: messenger)
        channel?.setStreamHandler(self)
        startTimer()
    }
    
    func startTimer() {
        let timer = Timer.scheduledTimer(timeInterval:1, target: self, selector:#selector(self.tickDown),userInfo:nil,repeats: true)
    }
    @objc func tickDown(){
        count += 1
        let args = ["count":count]
        if(events != nil){
            events!(args)
        }
    }
    
    public func onListen(withArguments arguments: Any?, eventSink events: @escaping FlutterEventSink) -> FlutterError? {
        self.events = events
        return nil;
    }
    
    public func onCancel(withArguments arguments: Any?) -> FlutterError? {
        self.events = nil
        return nil;
    }
}

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// Dart 
this.eventChannel = EventChannel("samples.flutter.dev.EventChannel");
this.eventChannel.receiveBroadcastStream().listen((event) {})

Tips：

五. 包体积增长和性能测试

在 iOS 平台上，跟据 App Store Connect 的数据，同一应用的发布 IPA 在 iPhone X 上的下载文件体积为 10.9 MB。 IPA 比 APK 大，主要是因为 Apple 加密了 IPA 中的二进制文件，使得压缩效率降低。（可以查看 iOS App Store Specific Considerations 中 QA1795 关于加密的部分）

Tips：

包体积优化>>

关于性能>>

六. 适用业务场景

几乎95%以上业务都能使用Flutter开发，即使flutter无法实现也能利用platformView进行原生视图托管实现。

七. 相关资料

翻译(二手)资料：

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