【Flutter 專題】58 圖解 Flutter 嵌入原生 AndroidView 小嚐試｜8月更文挑戰

      “這是我參與8月更文挑戰的第30天，活動詳情檢視： 8月更文挑戰” juejin.cn/post/698796…

      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 AndroidView iOS 端採用 UiKitView；小菜僅學習了 AndroidView 的基本用法；

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,
})
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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() {}
}
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2. 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()));
    }
}
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3. 在 MainActivity 中註冊該元件；

NLayoutFactory.registerWith(this);
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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() {}
}
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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); }
}
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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");
        }
    }
}
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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；

c. transparent

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

      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