Flutter 58: 图解 Flutter 嵌入原生 AndroidView 小尝试

      小菜前段时间学习了一下 Flutter 与原生 Android 之间的交互；是以 Android 为主工程，Flutter 作为 Module 方式进行交互；今天小菜尝试一下 Flutter 中嵌入 Native View 的交互方式；Android 端采用 AndroidView iOS 端采用 UiKitView；小菜仅学习了 AndroidView 的基本用法；

源码分析

const AndroidView({ Key key, @required this.viewType, this.onPlatformViewCreated, this.hitTestBehavior = PlatformViewHitTestBehavior.opaque, this.layoutDirection, this.gestureRecognizers, this.creationParams, this.creationParamsCodec, })

1. viewType -> 与 Android 原生交互时唯一标识符，常见形式是包名+自定义名；
2. onPlatformViewCreated -> 创建视图后的回调；
3. hitTestBehavior -> 渗透点击事件，接收范围 opaque > translucent > transparent；
4. layoutDirection -> 嵌入视图文本方向；
5. gestureRecognizers -> 可以传递到视图的手势集合；
6. creationParams -> 向视图传递参数，常为 PlatformViewFactory；
7. creationParamsCodec -> 编解码器类型；

基本用法

1. viewType

a. Android 端

1. 自定义 PlatformView，可根据需求实现 Channel 交互接口；

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. 创建 PlatformViewFactory 用于生成 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 中注册该组件；

NLayoutFactory.registerWith(this);

b. Flutter 端

      创建 AndroidView 并设置与原生相同的 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) ]);

c. 相关小结

1. 小菜对比两个 Container 高度，Container 尺寸大于 AndroidView 对应的原生 View 尺寸时，完全展示；相反小于时则会裁剪 AndroidView 对应的原生 View；
2. 两个 Container 背景色均未展示，小菜理解是 AndroidView 是填充满 Container 的，只是 AndroidView 中展示效果跟原生 View 尺寸相关；
3. AndroidView 中未填充满的部分会展示白色或黑色背景色，与 Android 主题版本 或 设备 相关；

2. creationParams / creationParamsCodec

      creationParams 与 creationParamsCodec 一般成对使用，creationParams 为默认传递参数，creationParamsCodec 为编解码器类型；

// Flutter 端 默认传递不同尺寸参数 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 与 Android 交互一般借助 MethodChannel / BasicMessageChannel / EventChannel 三种方式进行桥接交互；小菜以自定义 TextView 进行尝试；PlatformViewFactory 基本一致，只是更换初始化和注册的 N...TextView 即可；自定义 N...TextView 需实现各自的 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("我是来自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", "点击！"); 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) {} }

4. gestureRecognizers

      针对不同的 View 需要的手势有所不同，上述 TextView 没有设置手势集合，默认支持点击，但对于 ListView 之类的需要滑动手势或长按点击的话则需要添加 gestureRecognizers 手势集合；

// 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; } }

5. hitTestBehavior

      小菜尝试了数据绑定和手势操作，但重要的一点是数据透传，小菜在 Flutter / Android 两端添加了 Toast 进行测试；

a. opaque

      使用 PlatformViewHitTestBehavior.opaque 方式，两端均可监听处理，小菜理解，若有叠加 AndroidView 则不会透传到下一层；注意 PlatformView 只可在 AndroidView 范围内展示；

b. translucent

      使用 PlatformViewHitTestBehavior.translucent 方式，两端均可监听处理，小菜理解，若有叠加 AndroidView 则可以透传到下一层；

c. transparent

      使用 PlatformViewHitTestBehavior.transparent 方式，两端均不会透传展示；

      小菜在测试时，NMethodListView 设置高度超过剩余空间高度，例 Container 高度设置 500.0 可实际屏幕剩余高度只有 300.0，因 transparent 不会透传，所以 Flutter 外层 ListView 可以滑动，NMethodListView 不会滑动；使用 opaque / translucent 方式，NMethodListView 可以滑动，Flutter 外层 ListView 不能滑动，故有 200.0 高度展示不出来；

小结

1. 使用 AndroidView 时，Android API > 20；
2. 使用 AndroidView 时均需要有界父类；
3. 官网明确提醒，AndroidView 方式代价较大，由于是 GPU -> CPU -> GPU 有明显的性能缺陷，尽量避免使用；
4. 测试过程中热重载无效，每次均需重新编译；

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      小菜对两端的交互理解还不够深入，尤其是专有名词的理解还不到位，如有问题请多多指导！

来源：阿策小和尚