Flutter 58: 圖解 Flutter 嵌入原生 Android

Jack2k發表於2021-09-09
Flutter圖解Android

      小菜前段時間學習了一下 Flutter 與原生 Android 之間的互動；是以 Android 為主工程，Flutter 作為 Module 方式進行互動；今天小菜嘗試一下 Flutter 中嵌入 Native View 的互動方式；Android 端採用 iOS 端採用 ；小菜僅學習了 AndroidView 的基本用法；

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原始碼分析

const AndroidView({
    Key key,
    @required this.viewType,
    this.onPlatformViewCreated,
    this.hitTestBehavior = PlatformViewHitTestBehavior.opaque,
    this.layoutDirection,
    this.gestureRecognizers,
    this.creationParams,
    this.creationParamsCodec,
})
  1. viewType -> 與 Android 原生互動時唯一識別符號，常見形式是包名+自定義名；
  2. onPlatformViewCreated -> 建立檢視後的回撥；
  3. hitTestBehavior -> 滲透點選事件，接收範圍 opaque > translucent > transparent；
  4. layoutDirection -> 嵌入檢視文字方向；
  5. gestureRecognizers -> 可以傳遞到檢視的手勢集合；
  6. creationParams -> 向檢視傳遞引數，常為 PlatformViewFactory；
  7. creationParamsCodec -> 編解碼器型別；

基本用法

1. viewType

a. Android 端
  1. 自定義 PlatformView，可根據需求實現 Channel 互動介面；
public class NLayout implements PlatformView {
    private LinearLayout mLinearLayout;
    private BinaryMessenger messenger;

    NLayout(Context context, BinaryMessenger messenger, int id, Map<String, Object> params) {
        this.messenger = messenger;
        LinearLayout mLinearLayout = new LinearLayout(context);
        mLinearLayout.setBackgroundColor(Color.rgb(100, 200, 100));
        LinearLayout.LayoutParams lp = new LinearLayout.LayoutParams(900, 900);
        mLinearLayout.setLayoutParams(lp);
        this.mLinearLayout = mLinearLayout;
    }

    @Override
    public View getView() { return mLinearLayout; }

    @Override
    public void dispose() {}
}
  1. 建立 PlatformViewFactory 用於生成 PlatformView；
public class NLayoutFactory extends PlatformViewFactory {
    private final BinaryMessenger messenger;

    public NLayoutFactory(BinaryMessenger messenger) {
        super(StandardMessageCodec.INSTANCE);
        this.messenger = messenger;
    }

    @Override
    public PlatformView create(Context context, int i, Object o) {
        Map<String, Object> params = (Map<String, Object>) o;
        return new NLayout(context, messenger, i, params);
    }

    public static void registerWith(PluginRegistry registry) {
        final String key = "NLayout";
        if (registry.hasPlugin(key)) return;
        PluginRegistry.Registrar registrar = registry.registrarFor(key);
        registrar.platformViewRegistry().registerViewFactory("com.ace.ace_demo01/method_layout", new NLayoutFactory(registrar.messenger()));
    }
}
  1. 在 MainActivity 中註冊該元件；
NLayoutFactory.registerWith(this);
b. Flutter 端

      建立 AndroidView 並設定與原生相同的 viewType；

return ListView(children: <Widget>[
  Container(child: AndroidView(viewType: "com.ace.ace_demo01/method_layout"),
      color: Colors.pinkAccent, height: 400.0),
  Container(child: AndroidView(viewType: "com.ace.ace_demo01/method_layout"),
      color: Colors.greenAccent, height: 200.0)
]);

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c. 相關小結
  1. 小菜對比兩個 Container 高度，Container 尺寸大於 AndroidView 對應的原生 View 尺寸時，完全展示；相反小於時則會裁剪 AndroidView 對應的原生 View；
  2. 兩個 Container 背景色均未展示，小菜理解是 AndroidView 是填充滿 Container 的，只是 AndroidView 中展示效果跟原生 View 尺寸相關；
  3. AndroidView 中未填充滿的部分會展示白色或黑色背景色，與 Android 主題版本 或 裝置 相關；

2. creationParams / creationParamsCodec

      creationParams 與 creationParamsCodec 一般成對使用，creationParams 為預設傳遞引數，creationParamsCodec 為編解碼器型別；

// Flutter 端 預設傳遞不同尺寸引數
return ListView(children: <Widget>[
  Container(child: AndroidView(viewType: "com.ace.ace_demo01/method_layout0",
          creationParamsCodec: const StandardMessageCodec(),
          creationParams: {'method_layout_size': 150}),
      color: Colors.pinkAccent,height: 400.0),
  Container(child: AndroidView(viewType: "com.ace.ace_demo01/method_layout0",
          creationParamsCodec: const StandardMessageCodec(),
          creationParams: {'method_layout_size': 450}),
      color: Colors.greenAccent,height: 200.0)
]);

// Android NLayout
public class NLayout implements PlatformView {
    private LinearLayout mLinearLayout;
    private BinaryMessenger messenger;
    private int size = 0;

    NLayout(Context context, BinaryMessenger messenger, int id, Map<String, Object> params) {
        this.messenger = messenger;
        LinearLayout mLinearLayout = new LinearLayout(context);
        mLinearLayout.setBackgroundColor(Color.rgb(100, 200, 100));
        if (params != null && params.containsKey("method_layout_size")) {
            size = Integer.parseInt(params.get("method_layout_size").toString());
        } else {
            size = 900;
        }
        LinearLayout.LayoutParams lp = new LinearLayout.LayoutParams(size,size);
        mLinearLayout.setLayoutParams(lp);
        this.mLinearLayout = mLinearLayout;
    }

    @Override
    public View getView() { return mLinearLayout; }

    @Override
    public void dispose() {}
}

3. onPlatformViewCreated

      Flutter 與 Android 互動一般藉助 MethodChannel / BasicMessageChannel / EventChannel 三種方式進行橋接互動；小菜以自定義 TextView 進行嘗試；PlatformViewFactory 基本一致，只是更換初始化和註冊的 N…TextView 即可；自定義 N…TextView 需實現各自的 Channel 方式；

MethodChannel 方式
// Flutter 端
return Container(height: 80.0, child: AndroidView(
      onPlatformViewCreated: (id) async {
        MethodChannel _channel = const MethodChannel('ace_method_text_view');
        _channel..invokeMethod('method_set_text', 'Method_Channel')..setMethodCallHandler((call) {
            if (call.method == 'method_click') {
              _toast('Method Text FlutterToast!', context);
            }
          });
      },
      viewType: "com.ace.ace_demo01/method_text_view",
      creationParamsCodec: const StandardMessageCodec(),
      creationParams: {'method_text_str': 'Method Channel Params!!'}));

// Android NMethodTextView
public class NMethodTextView implements PlatformView, MethodChannel.MethodCallHandler {
    private TextView mTextView;
    private MethodChannel methodChannel;
    private BinaryMessenger messenger;

    NMethodTextView(Context context, BinaryMessenger messenger, int id, Map<String, Object> params) {
        this.messenger = messenger;
        TextView mTextView = new TextView(context);
        mTextView.setText("我是來自Android的原生TextView");
        mTextView.setBackgroundColor(Color.rgb(155, 205, 155));
        mTextView.setGravity(Gravity.CENTER);
        mTextView.setTextSize(16.0f);
        if (params != null && params.containsKey("method_text_str")) {
            mTextView.setText(params.get("method_text_str").toString());
        }
        this.mTextView = mTextView;

        methodChannel = new MethodChannel(messenger, "ace_method_text_view");
        methodChannel.setMethodCallHandler(this);

        mTextView.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                methodChannel.invokeMethod("method_click", "點選！");
                Toast.makeText(context, "Method Click NativeToast!", Toast.LENGTH_SHORT).show();
            }
        });
    }

    @Override
    public void onMethodCall(MethodCall methodCall, MethodChannel.Result result) {
        if (methodCall != null && methodCall.method.toString().equals("method_set_text")) {
            mTextView.setText(methodCall.arguments.toString());
            result.success("method_set_text_success");
        }
    }

    @Override
    public View getView() { return mTextView; }

    @Override
    public void dispose() { methodChannel.setMethodCallHandler(null); }
}
BasicMessageChannel 方式
// Flutter 端
return Container(height: 80.0, child: AndroidView(
      hitTestBehavior: PlatformViewHitTestBehavior.translucent,
      onPlatformViewCreated: (id) async {
        BasicMessageChannel _channel = const BasicMessageChannel('ace_basic_text_view', StringCodec());
        _channel..send("Basic_Channel")..setMessageHandler((message) {
            if (message == 'basic_text_click') {
              _toast('Basic Text FlutterToast!', context);
            }
            print('===${message.toString()}==');
          });
      },
      viewType: "com.ace.ace_demo01/basic_text_view",
      creationParamsCodec: const StandardMessageCodec(),
      creationParams: {'basic_text_str': 'Basic Channel Params!!'}));

// Android NBasicTextView
public class NBasicTextView implements PlatformView, BasicMessageChannel.MessageHandler {
    private TextView mTextView;
    private BasicMessageChannel basicMessageChannel;
    private BinaryMessenger messenger;

    NBasicTextView(Context context, BinaryMessenger messenger, int id, Map<String, Object> params) {
        this.messenger = messenger;
        TextView mTextView = new TextView(context);
        mTextView.setTextColor(Color.rgb(155, 155, 205));
        mTextView.setBackgroundColor(Color.rgb(155, 105, 155));
        mTextView.setGravity(Gravity.CENTER);
        mTextView.setTextSize(18.0f);
        if (params != null && params.containsKey("basic_text_str")) {
            mTextView.setText(params.get("basic_text_str").toString());
        }
        this.mTextView = mTextView;

        basicMessageChannel = new BasicMessageChannel(messenger, "ace_basic_text_view", StringCodec.INSTANCE);
        basicMessageChannel.setMessageHandler(this);

        mTextView.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                basicMessageChannel.send("basic_text_click");
                Toast.makeText(context, "Basic Click NativeToast!", Toast.LENGTH_SHORT).show();
            }
        });
    }

    @Override
    public View getView() { return mTextView; }

    @Override
    public void dispose() { basicMessageChannel.setMessageHandler(null); }

    @Override
    public void onMessage(Object o, BasicMessageChannel.Reply reply) {
        if (o != null){
            mTextView.setText(o.toString());
            basicMessageChannel.send("basic_set_text_success");
        }
    }
}
EventChannel 方式
// Flutter 端
return Container(height: 80.0, child: AndroidView(
      hitTestBehavior: PlatformViewHitTestBehavior.opaque,
      onPlatformViewCreated: (id) async {
        EventChannel _channel = const EventChannel('ace_event_text_view');
        _channel.receiveBroadcastStream('Event_Channel').listen((message) {
          if (message == 'event_text_click') {
            _toast('Event Text FlutterToast!', context);
          }
        });
      },
      viewType: "com.ace.ace_demo01/event_text_view",
      creationParamsCodec: const StandardMessageCodec(),
      creationParams: {'event_text_str': 'Event Channel Params!!'}));

// Android EventChannel
public class NEventTextView implements PlatformView, EventChannel.StreamHandler {
    private TextView mTextView;
    private EventChannel eventChannel;
    private BinaryMessenger messenger;

    NEventTextView(Context context, BinaryMessenger messenger, int id, Map<String, Object> params) {
        this.messenger = messenger;
        TextView mTextView = new TextView(context);
        mTextView.setTextColor(Color.rgb(250, 105, 25));
        mTextView.setBackgroundColor(Color.rgb(15, 200, 155));
        mTextView.setGravity(Gravity.CENTER);
        mTextView.setPadding(10, 10, 10, 10);
        mTextView.setTextSize(20.0f);
        if (params != null && params.containsKey("event_text_str")) {
            mTextView.setText(params.get("event_text_str").toString());
        }
        this.mTextView = mTextView;

        eventChannel = new EventChannel(messenger, "ace_event_text_view");
        eventChannel.setStreamHandler(this);

        mTextView.setOnClickListener(new View.OnClickListener() {

            @Override
            public void onClick(View v) {
                Toast.makeText(context, "Event Click NativeToast!", Toast.LENGTH_SHORT).show();
            }
        });
    }

    @Override
    public View getView() { return mTextView; }

    @Override
    public void dispose() { eventChannel.setStreamHandler(null); }

    @Override
    public void onListen(Object o, EventChannel.EventSink eventSink) {
        if (o != null) {
            mTextView.setText(o.toString());
            eventSink.success("event_set_text_success");
        }
    }

    @Override
    public void onCancel(Object o) {}
}

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4. gestureRecognizers

      針對不同的 View 需要的手勢有所不同，上述 TextView 沒有設定手勢集合，預設支援點選，但對於 ListView 之類的需要滑動手勢或長按點選的話則需要新增 gestureRecognizers 手勢集合；

// Flutter 端
return Container(height: 480.0,
    child: GestureDetector(
      child: AndroidView(
          gestureRecognizers: Set()..add(Factory<VerticalDragGestureRecognizer>(() => VerticalDragGestureRecognizer()))
            ..add(Factory<LongPressGestureRecognizer>(() => LongPressGestureRecognizer())),
          hitTestBehavior: PlatformViewHitTestBehavior.opaque,
          onPlatformViewCreated: (id) async {
            MethodChannel _channel = const MethodChannel('ace_method_list_view');
            _channel..invokeMethod('method_set_list', 15)..setMethodCallHandler((call) {
                if (call.method == 'method_item_click') {
                  _toast('List FlutterToast! position -> ${call.arguments}', context);
                } else if (call.method == 'method_item_long_click') {
                  _toast('List FlutterToast! -> ${call.arguments}', context);
                }
              });
          },
          viewType: "com.ace.ace_demo01/method_list_view",
          creationParamsCodec: const StandardMessageCodec(),
          creationParams: {'method_list_size': 10})));

// Android NMethodListView
public class NMethodListView implements PlatformView, MethodChannel.MethodCallHandler, ListView.OnItemClickListener, ListView.OnItemLongClickListener {

    private Context context;
    private ListView mListView;
    private MethodChannel methodChannel;
    private List<Map<String, String>> list = new ArrayList<>();
    private SimpleAdapter simpleAdapter = null;
    private int listSize = 0;

    NMethodListView(Context context, BinaryMessenger messenger, int id, Map<String, Object> params) {
        this.context = context;
        ListView mListView = new ListView(context);
        if (params != null && params.containsKey("method_list_size")) {
            listSize = Integer.parseInt(params.get("method_list_size").toString());
        }
        if (list != null) { list.clear(); }
        for (int i = 0; i < listSize; i++) {
            Map<String, String> map = new HashMap<>();
            map.put("id", "current item = " + (i + 1));
            list.add(map);
        }
        simpleAdapter = new SimpleAdapter(context, list, R.layout.list_item, new String[] { "id" }, new int[] { R.id.item_tv });
        mListView.setAdapter(simpleAdapter);
        mListView.setOnItemClickListener(this);
        mListView.setOnItemLongClickListener(this);
        this.mListView = mListView;

        methodChannel = new MethodChannel(messenger, "ace_method_list_view");
        methodChannel.setMethodCallHandler(this);
    }

    @Override
    public View getView() { return mListView; }

    @Override
    public void dispose() { methodChannel.setMethodCallHandler(null); }

    @Override
    public void onMethodCall(MethodCall methodCall, MethodChannel.Result result) {
        if (methodCall != null && methodCall.method.toString().equals("method_set_list")) {
            if (list != null) { list.clear(); }
            for (int i = 0; i < Integer.parseInt(methodCall.arguments.toString()); i++) {
                Map<String, String> map = new HashMap<>();
                map.put("id", "current item = " + (i + 1));
                list.add(map);
            }
            simpleAdapter.notifyDataSetChanged();
            result.success("method_set_list_success");
        }
    }

    @Override
    public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
        methodChannel.invokeMethod("method_item_click", position);
        Toast.makeText(context, "ListView.onItemClick NativeToast! position -> " + position, Toast.LENGTH_SHORT).show();
    }

    @Override
    public boolean onItemLongClick(AdapterView<?> parent, View view, int position, long id) {
        methodChannel.invokeMethod("method_item_long_click", list.get(position).get("id"));
        Toast.makeText(context, "ListView.onItemLongClick NativeToast! " + list.get(position).get("id"), Toast.LENGTH_SHORT).show();
        return true;
    }
}

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5. hitTestBehavior

      小菜嘗試了資料繫結和手勢操作，但重要的一點是資料透傳，小菜在 Flutter / Android 兩端新增了 Toast 進行測試；

a. opaque

      使用 PlatformViewHitTestBehavior.opaque 方式，兩端均可監聽處理，小菜理解，若有疊加 AndroidView 則不會透傳到下一層；注意 PlatformView 只可在 AndroidView 範圍內展示；

b. translucent

      使用 PlatformViewHitTestBehavior.translucent 方式，兩端均可監聽處理，小菜理解，若有疊加 AndroidView 則可以透傳到下一層；

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c. transparent

      使用 PlatformViewHitTestBehavior.transparent 方式，兩端均不會透傳展示；
圖片描述

      小菜在測試時，NMethodListView 設定高度超過剩餘空間高度，例 Container 高度設定 500.0 可實際螢幕剩餘高度只有 300.0，因 transparent 不會透傳，所以 Flutter 外層 ListView 可以滑動，NMethodListView 不會滑動；使用 opaque / translucent 方式，NMethodListView 可以滑動，Flutter 外層 ListView 不能滑動，故有 200.0 高度展示不出來；

小結

  1. 使用 AndroidView 時，Android API > 20；
  2. 使用 AndroidView 時均需要有界父類；
  3. 官網明確提醒，AndroidView 方式代價較大，由於是 GPU -> CPU -> GPU 有明顯的效能缺陷，儘量避免使用；
  4. 測試過程中熱過載無效，每次均需重新編譯；

      小菜對兩端的互動理解還不夠深入，尤其是專有名詞的理解還不到位，如有問題請多多指導！

來源：阿策小和尚

來自 “ ITPUB部落格 ” ，連結：http://blog.itpub.net/36/viewspace-2823620/，如需轉載，請註明出處，否則將追究法律責任。

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