我正在尝试创建一个通过workmanager插件调度的后台服务来触发简单通知的应用程序。这个想法是每15分钟检查一次mqtt实例中的任何消息，并在代理上有任何消息可用的情况下显示一个简单的本地通知。该通知也在应用程序初始化时被调用。主要问题是，无论我终止应用程序多少次并重新启动它，通知都可以正常运行，但是一旦我尝试调度后台服务，该服务就可以正常运行，但是本地通知插件无法初始化。
代码：
import 'dart:async';
import 'package:workmanager/workmanager.dart';
import 'package:flutter/material.dart';
import 'package:flutter_local_notifications/flutter_local_notifications.dart';
import './mqttClientWrapper.dart';
const mqtt_task_key = "MqttTask";
Future callbackDispatcher() async {
Workmanager.executeTask((taskName, inputData) async {
if (taskName == mqtt_task_key) {
print("running instance in background");
print("instantiating");
await RandomState().setup();
}
return Future.value(true);
});
}
class Random extends StatefulWidget {
@override
RandomState createState() => RandomState();
}
class RandomState extends State {
MQTTClientWrapper mqttClientWrapper;
String message = "";
Future setup() async {
FlutterLocalNotificationsPlugin flutterLocalNotificationsPlugin = FlutterLocalNotificationsPlugin();
mqttClientWrapper = MQTTClientWrapper(() => {}, (newMessage) => gotNewMessage(newMessage, flutterLocalNotificationsPlugin));
print('1');
mqttClientWrapper.prepareMqttClient();
print('2');
var initializationSettingsAndroid =
new AndroidInitializationSettings('@mipmap/ic_launcher');
print('3');
var initializationSettingsIOS = new IOSInitializationSettings();
var initializationSettings = new InitializationSettings(
initializationSettingsAndroid, initializationSettingsIOS);
//flutterLocalNotificationsPlugin = new FlutterLocalNotificationsPlugin();
await flutterLocalNotificationsPlugin.initialize(initializationSettings,
onSelectNotification: onSelectNotification);
}
Future gotNewMessage(String newMessage, flutterLocalNotificationsPlugin) async {
setState(() {
this.message = newMessage;
});
await _showNotificationWithDefaultSound(flutterLocalNotificationsPlugin);
print('test');
}
@override
void initState() {
super.initState();
setup();
Workmanager.cancelAll();
}
@override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(
title: Text('random'),
),
body: Center(
child: Column(
mainAxisAlignment: MainAxisAlignment.center,
children: [
Text(
message,
style: Theme.of(context).textTheme.headline4,
),
FlatButton(
color: Colors.blue,
onPressed: () {
Workmanager.initialize(
callbackDispatcher,
isInDebugMode: true,
);
print("initialized");
Workmanager.registerPeriodicTask('1', mqtt_task_key, frequency: Duration(minutes: 15), initialDelay: Duration(seconds: 30));
},
)
],
),
),
);
}
Future onSelectNotification(String payload) async {
showDialog(
context: context,
builder: (_) {
return new AlertDialog(
title: Text("PayLoad"),
content: Text("Payload : $payload"),
);
},
);
}
Future _showNotificationWithDefaultSound(flutterLocalNotificationsPlugin) async {
var androidPlatformChannelSpecifics = new AndroidNotificationDetails(
'your channel id', 'your channel name', 'your channel description',
importance: Importance.Max, priority: Priority.High);
var iOSPlatformChannelSpecifics = new IOSNotificationDetails();
var platformChannelSpecifics = new NotificationDetails(
androidPlatformChannelSpecifics, iOSPlatformChannelSpecifics);
await flutterLocalNotificationsPlugin.show(
0,
'New Post',
'New Message',
platformChannelSpecifics,
payload: 'Default_Sound',
);
}
}
控制台日志
I/flutter (16424): 1
I/flutter (16424): MQTTClientWrapper::test client connecting....
I/flutter (16424): 2020-08-19 04:01:10.452967 -- Authenticating with username '{wbynzcri}' and password '{uOIqIxMgf3Dl}'
I/flutter (16424): 2020-08-19 04:01:10.489029 -- SynchronousMqttServerConnectionHandler::internalConnect entered
I/flutter (16424): 2020-08-19 04:01:10.489300 -- SynchronousMqttServerConnectionHandler::internalConnect - initiating connection try 0
I/flutter (16424): 2020-08-19 04:01:10.489672 -- SynchronousMqttServerConnectionHandler::internalConnect - insecure TCP selected
I/flutter (16424): 2
I/flutter (16424): 3
I/flutter (16424): 2020-08-19 04:01:11.724721 -- MqttServerConnection::_startListening
I/flutter (16424): 2020-08-19 04:01:11.742755 -- SynchronousMqttServerConnectionHandler::internalConnect - connection complete
I/flutter (16424): 2020-08-19 04:01:11.743072 -- SynchronousMqttServerConnectionHandler::internalConnect sending connect message
I/flutter (16424): 2020-08-19 04:01:11.748088 -- MqttConnectionHandlerBase::sendMessage - MQTTMessage of type MqttMessageType.connect
I/flutter (16424): Header: MessageType = MqttMessageType.connect, Duplicate = false, Retain = false, Qos = MqttQos.atMostOnce, Size = 0
I/flutter (16424): Connect Variable Header: ProtocolName=MQIsdp, ProtocolVersion=3, ConnectFlags=Connect Flags: Reserved1=false, CleanStart=true, WillFlag=false, WillQos=MqttQos.atMostOnce, WillRetain=false, PasswordFlag=true, UserNameFlag=true, KeepAlive=60
I/flutter (16424): MqttConnectPayload - client identifier is : #
I/flutter (16424): 2020-08-19 04:01:11.780464 -- SynchronousMqttServerConnectionHandler::internalConnect - pre sleep, state = Connection status is connecting with return code of noneSpecified and a disconnection origin of none
I/flutter (16424): 2020-08-19 04:01:12.118299 -- MqttConnection::_onData
I/flutter (16424): 2020-08-19 04:01:12.137902 -- MqttServerConnection::_onData - message received MQTTMessage of type MqttMessageType.connectAck
I/flutter (16424): Header: MessageType = MqttMessageType.connectAck, Duplicate = false, Retain = false, Qos = MqttQos.atMostOnce, Size = 2
I/flutter (16424): Connect Variable Header: TopicNameCompressionResponse={0}, ReturnCode={MqttConnectReturnCode.connectionAccepted}
I/flutter (16424): 2020-08-19 04:01:12.144405 -- MqttServerConnection::_onData - message processed
I/flutter (16424): 2020-08-19 04:01:12.153670 -- SynchronousMqttServerConnectionHandler::_connectAckProcessor
I/flutter (16424): 2020-08-19 04:01:12.154185 -- SynchronousMqttServerConnectionHandler::_connectAckProcessor - state = connected
I/flutter (16424): MQTTClientWrapper::OnConnected client callback - Client connection was sucessful
I/flutter (16424): 2020-08-19 04:01:12.156048 -- SynchronousMqttServerConnectionHandler:: cancelling connect timer
I/flutter (16424): 2020-08-19 04:01:12.158088 -- SynchronousMqttServerConnectionHandler::internalConnect - post sleep, state = Connection status is connected with return code of connectionAccepted and a disconnection origin of none
I/flutter (16424): 2020-08-19 04:01:12.158600 -- SynchronousMqttServerConnectionHandler::internalConnect exited with state Connection status is connected with return code of connectionAccepted and a disconnection origin of none
I/flutter (16424): MQTTClientWrapper::Mosquitto client connected
I/flutter (16424): MQTTClientWrapper::Subscribing to the 4060431/# topic
I/flutter (16424): 2020-08-19 04:01:12.177163 -- MqttConnectionHandlerBase::sendMessage - MQTTMessage of type MqttMessageType.subscribe
I/flutter (16424): Header: MessageType = MqttMessageType.subscribe, Duplicate = false, Retain = false, Qos = MqttQos.atLeastOnce, Size = 0
I/flutter (16424): Subscribe Variable Header: MessageIdentifier={1}
I/flutter (16424): Payload: Subscription [{1}]
I/flutter (16424): {{ Topic={4060431/#}, Qos={MqttQos.atMostOnce} }}
I/flutter (16424):
I/flutter (16424): 2020-08-19 04:01:12.492990 -- MqttConnection::_onData
I/flutter (16424): 2020-08-19 04:01:12.500615 -- MqttServerConnection::_onData - message received MQTTMessage of type MqttMessageType.subscribeAck
I/flutter (16424): Header: MessageType = MqttMessageType.subscribeAck, Duplicate = false, Retain = false, Qos = MqttQos.atMostOnce, Size = 3
I/flutter (16424): SubscribeAck Variable Header: MessageIdentifier={1}
I/flutter (16424): Payload: Qos grants [{1}]
I/flutter (16424): {{ Grant={MqttQos.atMostOnce} }}
I/flutter (16424):
I/flutter (16424): 2020-08-19 04:01:12.501061 -- MqttServerConnection::_onData - message processed
I/flutter (16424): MQTTClientWrapper::Subscription confirmed for topic 4060431/#
I/flutter (16424): 2020-08-19 04:01:12.897098 -- MqttConnection::_onData
I/flutter (16424): 2020-08-19 04:01:12.920910 -- MqttServerConnection::_onData - message received MQTTMessage of type MqttMessageType.publish
I/flutter (16424): Header: MessageType = MqttMessageType.publish, Duplicate = false, Retain = true, Qos = MqttQos.atMostOnce, Size = 19
I/flutter (16424): Publish Variable Header: TopicName={4060431/offline/}, MessageIdentifier={0}, VH Length={18}
I/flutter (16424): Payload: {1 bytes={<49>
I/flutter (16424): 2020-08-19 04:01:12.921398 -- MqttServerConnection::_onData - message processed
I/flutter (16424): 2020-08-19 04:01:12.923384 -- MqttServerConnection::_onData - message received MQTTMessage of type MqttMessageType.publish
I/flutter (16424): Header: MessageType = MqttMessageType.publish, Duplicate = false, Retain = true, Qos = MqttQos.atMostOnce, Size = 45
I/flutter (16424): Publish Variable Header: TopicName={4060431/information/codename/}, MessageIdentifier={0}, VH Length={31}
I/flutter (16424): Payload: {14 bytes={<83><77><82><84><65><76><82><84><49><66><50><76><49><71>
I/flutter (16424): 2020-08-19 04:01:12.924024 -- MqttServerConnection::_onData - message processed
I/flutter (16424): 2020-08-19 04:01:12.926510 -- MqttServerConnection::_onData - message received MQTTMessage of type MqttMessageType.publish
I/flutter (16424): Header: MessageType = MqttMessageType.publish, Duplicate = false, Retain = true, Qos = MqttQos.atMostOnce, Size = 33
I/flutter (16424): Publish Variable Header: TopicName={4060431/information/version/}, MessageIdentifier={0}, VH Length={30}
I/flutter (16424): Payload: {3 bytes={<48><46><49>
I/flutter (16424): 2020-08-19 04:01:12.926893 -- MqttServerConnection::_onData - message processed
I/flutter (16424): 2020-08-19 04:01:12.928255 -- MqttServerConnection::_onData - message received MQTTMessage of type MqttMessageType.publish
I/flutter (16424): Header: MessageType = MqttMessageType.publish, Duplicate = false, Retain = true, Qos = MqttQos.atMostOnce, Size = 27
I/flutter (16424): Publish Variable Header: TopicName={4060431/sensor/0/type/}, MessageIdentifier={0}, VH Length={24}
I/flutter (16424): Payload: {3 bytes={<71><65><83>
I/flutter (16424): 2020-08-19 04:01:12.928666 -- MqttServerConnection::_onData - message processed
I/flutter (16424): 2020-08-19 04:01:12.929900 -- MqttServerConnection::_onData - message received MQTTMessage of type MqttMessageType.publish
I/flutter (16424): Header: MessageType = MqttMessageType.publish, Duplicate = false, Retain = true, Qos = MqttQos.atMostOnce, Size = 26
I/flutter (16424): Publish Variable Header: TopicName={4060431/sensor/0/state/}, MessageIdentifier={0}, VH Length={25}
I/flutter (16424): Payload: {1 bytes={<49>
I/flutter (16424): 2020-08-19 04:01:12.930394 -- MqttServerConnection::_onData - message processed
I/flutter (16424): MQTTClientWrapper::GOT A NEW MESSAGE 1
I/flutter (16424): MQTTClientWrapper::GOT A NEW MESSAGE SMRTALRT1B2L1G
I/flutter (16424): MQTTClientWrapper::GOT A NEW MESSAGE 0.1
I/flutter (16424): MQTTClientWrapper::GOT A NEW MESSAGE GAS
I/flutter (16424): MQTTClientWrapper::GOT A NEW MESSAGE 1
I/flutter (16424): test
I/flutter (16424): test
I/flutter (16424): test
I/flutter (16424): test
I/flutter (16424): test
I/art (16424): Do partial code cache collection, code=21KB, data=30KB
I/art (16424): After code cache collection, code=21KB, data=30KB
I/art (16424): Increasing code cache capacity to 128KB
I/flutter (16424): initialized
I/flutter (16424): 2020-08-19 04:01:30.486502 -- MqttConnectionHandlerBase::sendMessage - MQTTMessage of type MqttMessageType.pingRequest
I/flutter (16424): Header: MessageType = MqttMessageType.pingRequest, Duplicate = false, Retain = false, Qos = MqttQos.atMostOnce, Size = 0
I/flutter (16424): 2020-08-19 04:01:30.807658 -- MqttConnection::_onData
I/flutter (16424): 2020-08-19 04:01:30.811320 -- MqttServerConnection::_onData - message received MQTTMessage of type MqttMessageType.pingResponse
I/flutter (16424): Header: MessageType = MqttMessageType.pingResponse, Duplicate = false, Retain = false, Qos = MqttQos.atMostOnce, Size = 0
I/flutter (16424): 2020-08-19 04:01:30.812317 -- MqttServerConnection::_onData - message processed
I/flutter (16424): 2020-08-19 04:01:50.502517 -- MqttConnectionHandlerBase::sendMessage - MQTTMessage of type MqttMessageType.pingRequest
I/flutter (16424): Header: MessageType = MqttMessageType.pingRequest, Duplicate = false, Retain = false, Qos = MqttQos.atMostOnce, Size = 0
I/flutter (16424): 2020-08-19 04:01:50.833619 -- MqttConnection::_onData
I/flutter (16424): 2020-08-19 04:01:50.834847 -- MqttServerConnection::_onData - message received MQTTMessage of type MqttMessageType.pingResponse
I/flutter (16424): Header: MessageType = MqttMessageType.pingResponse, Duplicate = false, Retain = false, Qos = MqttQos.atMostOnce, Size = 0
I/flutter (16424): 2020-08-19 04:01:50.835866 -- MqttServerConnection::_onData - message processed
I/flutter (16424): running instance in background
I/flutter (16424): instantiating
I/flutter (16424): 1
I/flutter (16424): MQTTClientWrapper::test client connecting....
I/flutter (16424): 2020-08-19 04:01:53.864177 -- Authenticating with username '{wbynzcri}' and password '{uOIqIxMgf3Dl}'
I/flutter (16424): 2020-08-19 04:01:53.918924 -- SynchronousMqttServerConnectionHandler::internalConnect entered
I/flutter (16424): 2020-08-19 04:01:53.919223 -- SynchronousMqttServerConnectionHandler::internalConnect - initiating connection try 0
I/flutter (16424): 2020-08-19 04:01:53.919650 -- SynchronousMqttServerConnectionHandler::internalConnect - insecure TCP selected
I/flutter (16424): 2
E/MethodChannel#dexterous.com/flutter/local_notifications(16424): Failed to handle method call
E/MethodChannel#dexterous.com/flutter/local_notifications(16424): java.lang.NullPointerException: Attempt to invoke virtual method 'android.content.Intent android.app.Activity.getIntent()' on a null object reference
E/MethodChannel#dexterous.com/flutter/local_notifications(16424): at com.dexterous.flutterlocalnotifications.FlutterLocalNotificationsPlugin.initialize(FlutterLocalNotificationsPlugin.java:856)
E/MethodChannel#dexterous.com/flutter/local_notifications(16424): at com.dexterous.flutterlocalnotifications.FlutterLocalNotificationsPlugin.onMethodCall(FlutterLocalNotificationsPlugin.java:742)
E/MethodChannel#dexterous.com/flutter/local_notifications(16424): at io.flutter.plugin.common.MethodChannel$IncomingMethodCallHandler.onMessage(MethodChannel.java:226)
E/MethodChannel#dexterous.com/flutter/local_notifications(16424): at io.flutter.embedding.engine.dart.DartMessenger.handleMessageFromDart(DartMessenger.java:85)
E/MethodChannel#dexterous.com/flutter/local_notifications(16424): at io.flutter.embedding.engine.FlutterJNI.handlePlatformMessage(FlutterJNI.java:631)
E/MethodChannel#dexterous.com/flutter/local_notifications(16424): at android.os.MessageQueue.nativePollOnce(Native Method)
E/MethodChannel#dexterous.com/flutter/local_notifications(16424): at android.os.MessageQueue.next(MessageQueue.java:323)
E/MethodChannel#dexterous.com/flutter/local_notifications(16424): at android.os.Looper.loop(Looper.java:136)
E/MethodChannel#dexterous.com/flutter/local_notifications(16424): at android.app.ActivityThread.main(ActivityThread.java:6165)
E/MethodChannel#dexterous.com/flutter/local_notifications(16424): at java.lang.reflect.Method.invoke(Native Method)
E/MethodChannel#dexterous.com/flutter/local_notifications(16424): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:888)
E/MethodChannel#dexterous.com/flutter/local_notifications(16424): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:778)
I/WM-WorkerWrapper(16424): Worker result FAILURE for Work [ id=9519d0f6-1acd-445d-a325-8281ae5dd445, tags={ be.tramckrijte.workmanager.BackgroundWorker } ]
请注意，一旦启动了后台任务，初始化的命令就会打印在控制台上，并且实际执行任务与命令之间会有30秒的延迟，这就是为什么您会在它们之间看到mqtt实例消息。
主要问题开始于表单方法调用。