【Flutter 混合开发】嵌入原生View-Android

AndroidView

建议使用 Android Studio 进行开发，在 Android Studio 左侧 project tab下选中 android 目录下任意一个文件，右上角会出现 Open for Editing in Android Studio ，

点击即可打开，打开后 project tab 并不是一个 Android 项目，而是项目中所有 Android 项目，包含第三方：

app 目录是当前项目的 android 目录，其他则是第三方的 android 目录。

在App 项目的 java/包名 目录下创建嵌入 Flutter 中的 Android View，此 View 继承 PlatformView ：

class MyFlutterView(context: Context) : PlatformView {
override fun getView(): View {
TODO("Not yet implemented")
}

override fun dispose() {
TODO("Not yet implemented")
}
}

• getView ：返回要嵌入 Flutter 层次结构的Android View
• dispose：释放此View时调用，此方法调用后 View 不可用，此方法需要清除所有对象引用，否则会造成内存泄漏。

返回一个简单的 TextView ：

class MyFlutterView(context: Context, messenger: BinaryMessenger, viewId: Int, args: Map<String, Any>?) : PlatformView {

val textView: TextView = TextView(context)

init {
textView.text = "我是Android View"
}

override fun getView(): View {

return textView
}

override fun dispose() {
TODO("Not yet implemented")
}
}

• messenger：用于消息传递，后面介绍 Flutter 与 原生通信时用到此参数。
• viewId：View 生成时会分配一个唯一 ID。
• args：Flutter 传递的初始化参数。

注册PlatformView

创建PlatformViewFactory：

class MyFlutterViewFactory(val messenger: BinaryMessenger) : PlatformViewFactory(StandardMessageCodec.INSTANCE) {

override fun create(context: Context, viewId: Int, args: Any?): PlatformView {
val flutterView = MyFlutterView(context, messenger, viewId, args as Map<String, Any>?)
return flutterView
}

}

创建 MyPlugin ：

class MyPlugin : FlutterPlugin {

override fun onAttachedToEngine(binding: FlutterPlugin.FlutterPluginBinding) {
val messenger: BinaryMessenger = binding.binaryMessenger
binding
.platformViewRegistry
.registerViewFactory(
"plugins.flutter.io/custom_platform_view", MyFlutterViewFactory(messenger))
}

companion object {
@JvmStatic
fun registerWith(registrar: PluginRegistry.Registrar) {
registrar
.platformViewRegistry()
.registerViewFactory(
"plugins.flutter.io/custom_platform_view",
MyFlutterViewFactory(registrar.messenger()))
}
}

override fun onDetachedFromEngine(binding: FlutterPlugin.FlutterPluginBinding) {

}
}

记住 plugins.flutter.io/custom_platform_view ，这个字符串在 Flutter 中需要与其保持一致。

在 App 中 MainActivity 中注册：

class MainActivity : FlutterActivity() {
override fun configureFlutterEngine(flutterEngine: FlutterEngine) {
super.configureFlutterEngine(flutterEngine)
flutterEngine.plugins.add(MyPlugin())
}
}

如果是 Flutter Plugin，没有MainActivity，则在对应的 Plugin onAttachedToEngine 和 registerWith 方法修改如下：

public class CustomPlatformViewPlugin : FlutterPlugin,MethodCallHandler {
/// The MethodChannel that will the communication between Flutter and native Android
///
/// This local reference serves to register the plugin with the Flutter Engine and unregister it
/// when the Flutter Engine is detached from the Activity
private lateinit var channel: MethodChannel

override fun onAttachedToEngine(@NonNull flutterPluginBinding: FlutterPlugin.FlutterPluginBinding) {
channel = MethodChannel(flutterPluginBinding.getFlutterEngine().getDartExecutor(), "custom_platform_view")
channel.setMethodCallHandler(this)

val messenger: BinaryMessenger = flutterPluginBinding.binaryMessenger
flutterPluginBinding
.platformViewRegistry
.registerViewFactory(
"plugins.flutter.io/custom_platform_view", MyFlutterViewFactory(messenger))

}

// This static function is optional and equivalent to onAttachedToEngine. It supports the old
// pre-Flutter-1.12 Android projects. You are encouraged to continue supporting
// plugin registration via this function while apps migrate to use the new Android APIs
// post-flutter-1.12 via https://flutter.dev/go/android-project-migration.
//
// It is encouraged to share logic between onAttachedToEngine and registerWith to keep
// them functionally equivalent. Only one of onAttachedToEngine or registerWith will be called
// depending on the user's project. onAttachedToEngine or registerWith must both be defined
// in the same class.
companion object {
@JvmStatic
fun regist
56c
erWith(registrar: Registrar) {
val channel = MethodChannel(registrar.messenger(), "custom_platform_view")
channel.setMethodCallHandler(CustomPlatformViewPlugin())

registrar
.platformViewRegistry()
.registerViewFactory(
"plugins.flutter.io/custom_platform_view",
MyFlutterViewFactory(registrar.messenger()))
}
}

override fun onMethodCall(@NonNull call: MethodCall, @NonNull result: Result) {
if (call.method == "getPlatformVersion") {
result.success("Android ${android.os.Build.VERSION.RELEASE}")
} else {
result.notImplemented()
}
}

override fun onDetachedFromEngine(@NonNull binding: FlutterPlugin.FlutterPluginBinding) {
channel.setMethodCallHandler(null)
}
}

嵌入Flutter

在 Flutter 中调用

class PlatformViewDemo extends StatelessWidget {
@override
Widget build(BuildContext context) {
Widget platformView(){
if(defaultTargetPlatform == TargetPlatform.android){
return AndroidView(
viewType: 'plugins.flutter.io/custom_platform_view',
);
}
}
return Scaffold(
appBar: AppBar(),
body: Center(
child: platfor
ad0
mView(),
),
);
}
}

上面嵌入的是 Android View，因此通过 defaultTargetPlatform == TargetPlatform.android 判断当前平台加载，在 Android 上运行效果：

设置初始化参数

Flutter 端修改如下：

AndroidView(
viewType: 'plugins.flutter.io/custom_platform_view',
creationParams: {'text': 'Flutter传给AndroidTextView的参数'},
creationParamsCodec: StandardMessageCodec(),
)

• creationParams ：传递的参数，插件可以将此参数传递给 AndroidView 的构造函数。
• creationParamsCodec ：将 creationParams 编码后再发送给平台侧，它应该与传递给构造函数的编解码器匹配。值的范围： StandardMessageCodec
• JSONMessageCodec
• StringCodec
• BinaryCodec

修改 MyFlutterView ：

class MyFlutterView(context: Context, messenger: BinaryMessenger, viewId: Int, args: Map<String, Any>?) : PlatformView {

val textView: TextView = TextView(context)

init {
args?.also {
textView.text = it["text"] as String
}
}

override fun getView(): View {

return textView
}

override fun dispose() {
TODO("Not yet implemented")
}
}

最终效果：

Flutter 向 Android View 发送消息

修改 Flutter 端，创建 MethodChannel 用于通信：

class PlatformViewDemo extends StatefulWidget {
@override
_PlatformViewDemoState createState() => _PlatformViewDemoState();
}

class _PlatformViewDemoState extends State<PlatformViewDemo> {
static const platform =
const MethodChannel('com.flutter.guide.MyFlutterView');

@override
Widget build(BuildContext context) {
Widget platformView() {
if (defaultTargetPlatform == TargetPlatform.android) {
return AndroidView(
viewType: 'plugins.flutter.io/custom_platform_view',
creationParams: {'text': 'Flutter传给AndroidTextView的参数'},
creationParamsCodec: StandardMessageCodec(),
);
}
}

return Scaffold(
appBar: AppBar(),
body: Column(children: [
RaisedButton(

56c
child: Text('传递参数给原生View'),
onPressed: () {
platform.invokeMethod('setText', {'name': 'laomeng', 'age': 18});
},
),
Expanded(child: platformView()),
]),
);
}
}

在 原生View 中也创建一个 MethodChannel 用于通信：

class MyFlutterView(context: Context, messenger: BinaryMessenger, viewId: Int, args: Map<String, Any>?) : PlatformView, MethodChannel.MethodCallHandler {

val textView: TextView = TextView(context)
private var methodChannel: MethodChannel

init {
args?.also {
textView.text = it["text"] as String
}
methodChannel = MethodChannel(messenger, "com.flutter.guide.MyFlutterView")
methodChannel.setMethodCallHandler(this)
}

override fun getView(): View {

return textView
}

override fun dispose() {
methodChannel.setMethodCallHandler(null)
}

override fun onMethodCall(call: MethodCall, result: MethodChannel.Result) {
if (call.method == "setText") {
val name = call.argument("name") as String?
val age = call.argument("age") as Int?

textView.text = "hello,$name,年龄：$age"
} else {
result.notImplemented()
}
}
}

Flutter 向 Android View 获取消息

与上面发送信息不同的是，Flutter 向原生请求数据，原生返回数据到 Flutter 端，修改 MyFlutterView onMethodCall：

override fun onMethodCall(call: MethodCall, result: MethodChannel.Result) {
if (call.method == "setText") {
val name = call.argument("name") as String?
val age = call.argument("age") as Int?
textView.text = "hello,$name,年龄：$age"
} else if (call.method == "getData") {
val name = call.argument("name") as String?
val age = call.argument("age") as Int?

var map = mapOf("name" to "hello,$name",
"age" to "$age"
)
result.success(map)
} else {
result.notImplemented()
}
}

result.success(map) 是返回的数据。

Flutter 端接收数据：

var _data = '获取数据';

RaisedButton(
child: Text('$_data'),
onPressed: () async {
var result = await platform
.invokeMethod('getData', {'name': 'laomeng', 'age': 18});
setState(() {
_data = '${result['name']},${result['age']}';
ad8

});
},
),

解决多个原生View通信冲突问题

当然页面有3个原生View，

class PlatformViewDemo extends StatefulWidget {
@override
_PlatformViewDemoState createState() => _PlatformViewDemoState();
}

class _PlatformViewDemoState extends State<PlatformViewDemo> {
static const platform =
const MethodChannel('com.flutter.guide.MyFlutterView');

var _data = '获取数据';

@override
Widget build(BuildContext context) {
Widget platformView() {
if (defaultTargetPlatform == TargetPlatform.android) {
return AndroidView(
viewType: 'plugins.flutter.io/custom_platform_view',
creationParams: {'text': 'Flutter传给AndroidTextView的参数'},
creationParamsCodec: StandardMessageCodec(),
);
}
}

return Scaffold(
appBar: AppBar(),
body: Column(children: [
Row(
children: [
RaisedButton(
child: Text('传递参数给原生View'),
onPressed: () {
platform
.invokeMethod('setText', {'name': 'laomeng', 'age': 18});
},
),
RaisedButton(
child: Text('$_data'),
onPressed: () async {
var result = await platform
.invokeMethod('getData', {'name': 'laomeng', 'age': 18});
setState(() {
_data = '${result['name']},${result['age']}';
});
},
),
],
),
Expanded(child: Container(color: Colors.red, child: platformView())),
Expanded(child: Container(color: Colors.blue, child: platformView())),
Expanded(child: Container(color: Colors.yellow, child: platformView())),
]),
);
}
}

此时点击 传递参数给原生View 按钮哪个View会改变内容，实际上只有最后一个会改变。

如何改变指定View的内容？重点是 MethodChannel，只需修改上面3个通道的名称不相同即可：

• 第一种方法：将一个唯一 id 通过初始化参数传递给原生 View，原生 View使用这个id 构建不同名称的 MethodChannel。
• 第二种方法（推荐）：原生 View 生成时，系统会为其生成唯一id：view 1044 Id，使用 viewId 构建不同名称的 MethodChannel。

原生 View 使用 viewId 构建不同名称的 MethodChannel：

class MyFlutterView(context: Context, messenger: BinaryMessenger, viewId: Int, args: Map<String, Any>?) : PlatformView, MethodChannel.MethodCallHandler {

val textView: TextView = TextView(context)
private var methodChannel: MethodChannel

init {
args?.also {
textView.text = it["text"] as String
}
methodChannel = MethodChannel(messenger, "com.flutter.guide.MyFlutterView_$viewId")
methodChannel.setMethodCallHandler(this)
}
...
}

Flutter 端为每一个原生 View 创建不同的MethodChannel：

var platforms = [];

AndroidView(
viewType: 'plugins.flutter.io/custom_platform_view',
onPlatformViewCreated: (viewId) {
print('viewId:$viewId');
platforms
.add(MethodChannel('com.flutter.guide.MyFlutterView_$viewId'));
},
creationParams: {'text': 'Flutter传给AndroidTextView的参数'},
creationParamsCodec: StandardMessageCodec(),
)

给第一个发送消息：

platforms[0]
.invokeMethod('setText', {'name': 'laomeng', 'age': 18});

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