android - 从原生 Android 主屏幕小部件调用 Flutter (Dart) 代码

Question

我向我的 Flutter 应用程序添加了一个原生 Android 主屏幕小部件。

在我的 AppWidgetProvider 实现中，我想使用平台 channel 在 onUpdate() 方法中调用 dart 代码。

这可能吗？如果可以，如何实现？

我当前的 Android (Java) 代码:

package com.westy92.checkiday;

import android.appwidget.AppWidgetManager;
import android.appwidget.AppWidgetProvider;
import android.content.Context;
import android.util.Log;

import io.flutter.plugin.common.MethodChannel;
import io.flutter.view.FlutterNativeView;

public class HomeScreenWidget extends AppWidgetProvider {

    private static final String TAG = "HomeScreenWidget";
    private static final String CHANNEL = "com.westy92.checkiday/widget";

    private static FlutterNativeView backgroundFlutterView = null;
    private static MethodChannel channel = null;

    @Override
    public void onEnabled(Context context) {
        Log.i(TAG, "onEnabled!");
        backgroundFlutterView = new FlutterNativeView(context, true);
        channel = new MethodChannel(backgroundFlutterView, CHANNEL);
    }

    @Override
    public void onUpdate(Context context, AppWidgetManager appWidgetManager, int[] appWidgetIds) {
        Log.i(TAG, "onUpdate!");
        if (channel != null) {
            Log.i(TAG, "channel not null, invoking dart method!");
            channel.invokeMethod("foo", "extraJunk");
            Log.i(TAG, "after invoke dart method!");
        }
    }
}

Dart 代码:

void main() {
  runApp(Checkiday());
}

class Checkiday extends StatefulWidget {
  @override
  _CheckidayState createState() => _CheckidayState();
}

class _CheckidayState extends State<Checkiday> {
  static const MethodChannel platform = MethodChannel('com.westy92.checkiday/widget');

  @override
  void initState() {
    super.initState();
    platform.setMethodCallHandler(nativeMethodCallHandler);
  }

  Future<dynamic> nativeMethodCallHandler(MethodCall methodCall) async {
    print('Native call!');
    switch (methodCall.method) {
      case 'foo':
        return 'some string';
      default:
      // todo - throw not implemented
    }
  }

  @override
  Widget build(BuildContext context) {
    // ...
  }
}

当我将小部件添加到主屏幕时，我看到:

I/HomeScreenWidget(10999): onEnabled!
I/HomeScreenWidget(10999): onUpdate!
I/HomeScreenWidget(10999): channel not null, invoking dart method!
I/HomeScreenWidget(10999): after invoke dart method!

但是，我的 dart 代码似乎没有收到调用。

Answer 1

我还需要一些原生的 android 小部件来与我的 dart 代码进行通信，经过一些修补后，我设法做到了。在我看来，关于如何做到这一点的文档有点稀少，但我凭借一点创造力设法让它发挥作用。我还没有做足够的测试来称这个 100% 生产就绪，但它似乎正在工作......

Dart 设置

转到 main.dart 并添加以下顶级函数:

void initializeAndroidWidgets() {
  if (Platform.isAndroid) {
    // Intialize flutter
    WidgetsFlutterBinding.ensureInitialized();

    const MethodChannel channel = MethodChannel('com.example.app/widget');

    final CallbackHandle callback = PluginUtilities.getCallbackHandle(onWidgetUpdate);
    final handle = callback.toRawHandle();

    channel.invokeMethod('initialize', handle);
  }
}

然后在运行您的应用程序之前调用此函数

void main() {
  initializeAndroidWidgets();
  runApp(MyApp());
}

这将确保我们可以在 native 端为我们的入口点获取回调句柄。

现在像这样添加一个入口点:

void onWidgetUpdate() {
  // Intialize flutter
  WidgetsFlutterBinding.ensureInitialized();

  const MethodChannel channel = MethodChannel('com.example.app/widget');

  // If you use dependency injection you will need to inject
  // your objects before using them.

  channel.setMethodCallHandler(
    (call) async {
      final id = call.arguments;

      print('on Dart ${call.method}!');

      // Do your stuff here...
      final result = Random().nextDouble();

      return {
        // Pass back the id of the widget so we can
        // update it later
        'id': id,
        // Some data
        'value': result,
      };
    },
  );
}

这个函数将成为我们的小部件的入口点，并在我们的小部件 onUpdate 方法被调用时被调用。然后我们可以传回一些数据(例如在调用 api 之后)。

Android 设置

这里的示例在 Kotlin 中，但在 Java 中也应该进行一些小的调整。

创建一个 WidgetHelper 类，它将帮助我们存储和获取入口点的句柄:

class WidgetHelper {
    companion object  {
        private const val WIDGET_PREFERENCES_KEY = "widget_preferences"
        private const val WIDGET_HANDLE_KEY = "handle"

        const val CHANNEL = "com.example.app/widget"
        const val NO_HANDLE = -1L

        fun setHandle(context: Context, handle: Long) {
            context.getSharedPreferences(
                WIDGET_PREFERENCES_KEY,
                Context.MODE_PRIVATE
            ).edit().apply {
                putLong(WIDGET_HANDLE_KEY, handle)
                apply()
            }
        }

        fun getRawHandle(context: Context): Long {
            return context.getSharedPreferences(
                WIDGET_PREFERENCES_KEY,
                Context.MODE_PRIVATE
            ).getLong(WIDGET_HANDLE_KEY, NO_HANDLE)
        }
    }
}

将您的 MainActivity 替换为:

class MainActivity : FlutterActivity(), MethodChannel.MethodCallHandler {
    override fun configureFlutterEngine(@NonNull flutterEngine: FlutterEngine) {
        GeneratedPluginRegistrant.registerWith(flutterEngine)

        val channel = MethodChannel(flutterEngine.dartExecutor.binaryMessenger, WidgetHelper.CHANNEL)
        channel.setMethodCallHandler(this)
    }

    override fun onMethodCall(call: MethodCall, result: MethodChannel.Result) {
        when (call.method) {
            "initialize" -> {
                if (call.arguments == null) return
                WidgetHelper.setHandle(this, call.arguments as Long)
            }
        }
    }
}

这将确保我们将句柄(入口点的哈希)存储到 SharedPreferences 以便稍后在小部件中检索它。

现在修改您的 AppWidgetProvider 使其看起来类似于以下内容:

class Foo : AppWidgetProvider(), MethodChannel.Result {

    private val TAG = this::class.java.simpleName

    companion object {
        private var channel: MethodChannel? = null;
    }

    private lateinit var context: Context

    override fun onUpdate(context: Context, appWidgetManager: AppWidgetManager, appWidgetIds: IntArray) {
        this.context = context

        initializeFlutter()

        for (appWidgetId in appWidgetIds) {
            updateWidget("onUpdate ${Math.random()}", appWidgetId, context)
            // Pass over the id so we can update it later...
            channel?.invokeMethod("update", appWidgetId, this)
        }
    }

    private fun initializeFlutter() {
        if (channel == null) {
            FlutterMain.startInitialization(context)
            FlutterMain.ensureInitializationComplete(context, arrayOf())

            val handle = WidgetHelper.getRawHandle(context)
            if (handle == WidgetHelper.NO_HANDLE) {
                Log.w(TAG, "Couldn't update widget because there is no handle stored!")
                return
            }

            val callbackInfo = FlutterCallbackInformation.lookupCallbackInformation(handle)

            // Instantiate a FlutterEngine.
            val engine = FlutterEngine(context.applicationContext)
            val callback = DartExecutor.DartCallback(context.assets, loader.findAppBundlePath(), callbackInfo)
            engine.dartExecutor.executeDartCallback(callback)

            channel = MethodChannel(engine.dartExecutor.binaryMessenger, WidgetHelper.CHANNEL)
        }
    }

    override fun success(result: Any?) {
        Log.d(TAG, "success $result")

        val args = result as HashMap<*, *>
        val id = args["id"] as Int
        val value = args["value"] as Int

        updateWidget("onDart $value", id, context)
    }

    override fun notImplemented() {
        Log.d(TAG, "notImplemented")
    }

    override fun error(errorCode: String?, errorMessage: String?, errorDetails: Any?) {
        Log.d(TAG, "onError $errorCode")
    }

    override fun onDisabled(context: Context?) {
        super.onDisabled(context)
        channel = null
    }
}

internal fun updateWidget(text: String, id: Int, context: Context) {
    val views = RemoteViews(context.packageName, R.layout.small_widget).apply {
        setTextViewText(R.id.appwidget_text, text)
    }

    val manager = AppWidgetManager.getInstance(context)
    manager.updateAppWidget(id, views)
}

这里重要的是 initializeFlutter，它将确保我们能够获得入口点的句柄。然后在 onUpdate 中调用 channel?.invokeMethod("update", appWidgetId, this) ，这将在我们的 MethodChannel 中触发回调前面定义的 Dart 端。然后我们稍后在 success 中处理结果(至少在调用成功时)。

希望这能让您大致了解如何实现这一目标...