android - android 应用程序类启动时运行 flutter 代码

Question

我正在为 Flutter 制作一个插件，以使用 android native 库处理 fcm 消息。

正如我们所知，当 FCM 收到一条消息时，它会启动应用程序(它是应用程序类)并运行 Application#onCreate block 中的代码，因此我们可以在应用程序启动时运行 native 代码fcm 在后台。

我的问题是，是否可以在应用程序启动时运行 flutter 代码？
例如，如果收到消息:

应用类:

public class Application extends FlutterApplication {

  @Override
  public void onCreate() {
    super.onCreate();
    // Start flutter engine
    // Invoke a dart code in the Plugin using methodChannel or etc.
  }
}

Answer 1

简短回答，是

您可以使用它的句柄键在后台调用 Dart 方法。

1。在后台注册你的插件

实现自定义应用程序类(覆盖 FlutterApplication )

public class MyApp extends FlutterApplication implements PluginRegistry.PluginRegistrantCallback {

    @Override
    public void registerWith(io.flutter.plugin.common.PluginRegistry registry) {
        // For apps using FlutterEmbedding v1
        GeneratedPluginRegistrant.registerWith(registry);
       // App with V2 will initialize plugins automatically, you might need to register your own however
    }
}

记得在AndroidManifest中注册类(class)通过添加 android:name=".MyApp"至 <application>属性。

What is embedding v2?

2。在您的 Flutter 代码中创建一个设置函数作为顶级函数

/// Define this TopLevel or static
void _setup() async {
  MethodChannel backgroundChannel = const MethodChannel('flutter_background');
  // Setup Flutter state needed for MethodChannels.
  WidgetsFlutterBinding.ensureInitialized();

  // This is where the magic happens and we handle background events from the
  // native portion of the plugin.
  backgroundChannel.setMethodCallHandler((MethodCall call) async {
    if (call.method == 'handleBackgroundMessage') {
      final CallbackHandle handle =
          CallbackHandle.fromRawHandle(call.arguments['handle']);
      final Function handlerFunction =
          PluginUtilities.getCallbackFromHandle(handle);
      try {
        var dataArg = call.arguments['message'];
        if (dataArg == null) {
          print('Data received from callback is null');
          return;
        }
        await handlerFunction(dataArg);
      } catch (e) {
        print('Unable to handle incoming background message.\n$e');
      }
    }
    return Future.value();
  });

3。创建一个顶级回调，它将获取后台消息并调用它

_bgFunction(dynamic message) {
    // Message received in background
    // Remember, this will be a different isolate. So, no widgets
}

4。获取后台函数的handle key和setup通过MethodChannel发送给native

// dart:ui needed
CallbackHandle setup PluginUtilities.getCallbackHandle(_setup);
CallbackHandle handle PluginUtilities.getCallbackHandle(_bgFunction);

_channel.invokeMethod<bool>(
  'handleFunction',
  <String, dynamic>{
    'handle': handle.toRawHandle(),
    'setup': setup.toRawHandle()
  },
);

5。保存到原生端的SharedPref中

public void onMethodCall(MethodCall call, MethodChannel.Result result) {
  String methodName = call.method
  if (methodName == "handleFunction") {
     long handle = call.argument("handle");
     long setup = call.argument("setup");
     // save them
  }
}

6。后台唤醒后，启动后台隔离

FlutterMain.ensureInitializationComplete(context, null)
val appBundlePath = FlutterMain.findAppBundlePath()
val flutterCallback = FlutterCallbackInformation.lookupCallbackInformation(setupHandleYouHadSaved)

FlutterNativeView backgroundFlutterView = FlutterNativeView(context, true)

val args = FlutterRunArguments()
args.bundlePath = appBundlePath
args.entrypoint = flutterCallback.callbackName
args.libraryPath = flutterCallback.callbackLibraryPath

backgroundFlutterView?.runFromBundle(args)

// Initialize your registrant in the app class
pluginRegistrantCallback?.registerWith(backgroundFlutterView?.pluginRegistry)

7.当您的插件注册后，创建一个后台 channel 并将其传递给

val backgroundChannel = MethodChannel(messenger, "pushe_flutter_background")

8.调用将调用的设置方法并将消息提供给回调

private fun sendBackgroundMessageToExecute(context: Context, message: String) {
    if (backgroundChannel == null) {
        return
    }

    val args: MutableMap<String, Any?> = HashMap()
    if (backgroundMessageHandle == null) {
        backgroundMessageHandle = getMessageHandle(context)
    }
    args["handle"] = backgroundMessageHandle
    args["message"] = message
    // The created background channel at step 7
    backgroundChannel?.invokeMethod("handleBackgroundMessage", args, null)
}

sendBackgroundMessageToExecute将执行飞镖 _setup函数并传递消息和回调句柄。在第2步中，将调用回调。

Note: There are still certain corner cases you may want to consider (for instance thread waiting and ...). Checkout the samples and see the source code.

有几个项目支持应用在后台启动时后台执行。

FirebaseMessaging

Pushe

WorkManager