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bkonyi [android_alarm_manager] Fixed issue where callback lookup was failing…
… in the background (#2453)

If callback lookup was attempted before Flutter was initialized, the
callback cache would not yet be populated resulting in a failed callback
lookup.
Latest commit de56da5 Jan 9, 2020

README.md

android_alarm_manager

pub package

A Flutter plugin for accessing the Android AlarmManager service, and running Dart code in the background when alarms fire.

Getting Started

After importing this plugin to your project as usual, add the following to your AndroidManifest.xml within the <manifest></manifest> tags:

<uses-permission android:name="android.permission.RECEIVE_BOOT_COMPLETED"/>
<uses-permission android:name="android.permission.WAKE_LOCK"/>

Next, within the <application></application> tags, add:

<service
    android:name="io.flutter.plugins.androidalarmmanager.AlarmService"
    android:permission="android.permission.BIND_JOB_SERVICE"
    android:exported="false"/>
<receiver
    android:name="io.flutter.plugins.androidalarmmanager.AlarmBroadcastReceiver"
    android:exported="false"/>
<receiver
    android:name="io.flutter.plugins.androidalarmmanager.RebootBroadcastReceiver"
    android:enabled="false">
    <intent-filter>
        <action android:name="android.intent.action.BOOT_COMPLETED"></action>
    </intent-filter>
</receiver>

Then in Dart code add:

import 'package:android_alarm_manager/android_alarm_manager.dart';

void printHello() {
  final DateTime now = DateTime.now();
  final int isolateId = Isolate.current.hashCode;
  print("[$now] Hello, world! isolate=${isolateId} function='$printHello'");
}

main() async {
  final int helloAlarmID = 0;
  await AndroidAlarmManager.initialize();
  runApp(...);
  await AndroidAlarmManager.periodic(const Duration(minutes: 1), helloAlarmID, printHello);
}

printHello will then run (roughly) every minute, even if the main app ends. However, printHello will not run in the same isolate as the main application. Unlike threads, isolates do not share memory and communication between isolates must be done via message passing (see more documentation on isolates here).

Using other plugins in alarm callbacks

If alarm callbacks will need access to other Flutter plugins, including the alarm manager plugin itself, it may be necessary to inform the background service how to initialize plugins depending on which Flutter Android embedding the application is using.

Flutter Android Embedding V1

For the Flutter Android Embedding V1, the background service must be provided a callback to register plugins with the background isolate. This is done by giving the AlarmService a callback to call the application's onCreate method. See the example's Application overrides.

In particular, its Application class is as follows:

public class Application extends FlutterApplication implements PluginRegistrantCallback {
  @Override
  public void onCreate() {
    super.onCreate();
    AlarmService.setPluginRegistrant(this);
  }

  @Override
  public void registerWith(PluginRegistry registry) {
    GeneratedPluginRegistrant.registerWith(registry);
  }
}

Which must be reflected in the application's AndroidManifest.xml. E.g.:

    <application
        android:name=".Application"
        ...

Note: Not calling AlarmService.setPluginRegistrant will result in an exception being thrown when an alarm eventually fires.

Flutter Android Embedding V2 (Flutter Version >= 1.12)

For the Flutter Android Embedding V2, plugins are registered with the background isolate via reflection so AlarmService.setPluginRegistrant does not need to be called.

NOTE: this plugin is not completely compatible with the V2 embedding on Flutter versions < 1.12 as the background isolate will not automatically register plugins. This can be resolved by running flutter upgrade to upgrade to the latest Flutter version.

For help getting started with Flutter, view our online documentation.

For help on editing plugin code, view the documentation.

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