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我想在flutter（android应用程序）中设置本地通知，我了解了workmanager包，但我不知道如何将它用于我的目的。我想在用户选择的确切时间发送通知。

时间选择：

Container(
          padding: EdgeInsets.all(15),
          child: IconButton(icon: Icon(Icons.alarm, color: Colors.white, size: 70,),
              onPressed: (){
                DatePicker.showTimePicker(context,
                    theme: DatePickerTheme(
                      containerHeight: 210.0,
                    ),
                    showTitleActions: true, onConfirm: (time) {
                      ttime = '${time.hour} : ${time.minute} : ${time.second}';
                      //print(_time);
                      _setNotifyTime();
                      setState(() {});
                    }, currentTime: DateTime.now(), locale: LocaleType.en);
                setState(() {});
              }),
        ),

将这段时间保存在共享首选项中：

Future<void> _setNotifyTime() async{
final prefs = await SharedPreferences.getInstance();
final savedNotifyTime = await _getStringFromSharedPrefs();
await prefs.setString('notificationTime', ttime);
//print("this $savedNotifyTime");
return savedNotifyTime;
}

从共享偏好中获取这个时间：

Future<String> _getStringFromSharedPrefs() async{
final prefs = await SharedPreferences.getInstance();
notifyTime = prefs.getString('notificationTime');
return notifyTime;
}

根据所选时间颤振本地通知：

Future<void> showDailyAtTime() async {
var splited = notifyTime.split(':');
int hour = int.parse(splited[0]);
int minute = int.parse(splited[1]);
int second = int.parse(splited[2]);
print(hour.toString());
print(minute.toString());
print(second.toString());
var reviewTime = Time(hour, minute, second);
var androidChannelSpecifics = AndroidNotificationDetails(
  'CHANNEL_ID 2',
  'CHANNEL_NAME 2',
  "CHANNEL_DESCRIPTION 2",
  importance: Importance.max,
  priority: Priority.high,
);
var iosChannelSpecifics = IOSNotificationDetails();
var platformChannelSpecifics =
NotificationDetails(android: androidChannelSpecifics, iOS: iosChannelSpecifics);
await flutterLocalNotificationsPlugin.showDailyAtTime(
  0,
  'Title at ${reviewTime.hour}:${reviewTime.minute}.${reviewTime.second}',
  'Test Body', //null
  reviewTime,
  platformChannelSpecifics,
  payload: 'Test Payload',
 );
}

工作管理器实现：

void callbackDispatcher() {
Workmanager().executeTask((taskName, inputData) async {
notificationPlugin.showDailyAtTime();
return Future.value(true);
 });
}

void main() async {
 WidgetsFlutterBinding.ensureInitialized();
 await Workmanager().initialize(callbackDispatcher);
 await Workmanager().registerPeriodicTask("test_workertask", "test_workertask",
 inputData: {"data1": "value1", "data2": "value2"},
 frequency: Duration(minutes: 15),
 initialDelay: Duration(minutes: 15));
 runApp(MyApp());
}

当我从应用程序内的按钮调用它时这是有效的，但是一旦我进入后台它就不起作用。当我实现上面的代码时，它给出了以下错误：

HostComposition ext ANDROID_EMU_CHECKSUM_HELPER_v1 ANDROID_EMU_dma_v1   ANDROID_EMU_direct_mem ANDROID_EMU_host_composition_v1  ANDROID_EMU_host_composition_v2 ANDROID_EMU_vulkan  ANDROID_EMU_deferred_vulkan_commands ANDROID_EMU_vulkan_null_optional_strings  ANDROID_EMU_vulkan_create_resources_with_requirements ANDROID_EMU_YUV_Cache  ANDROID_EMU_async_unmap_buffer ANDROID_EMU_vulkan_ignored_handles  ANDROID_EMU_vulkan_free_memory_sync ANDROID_EMU_vulkan_shader_float16_int8  ANDROID_EMU_vulkan_async_queue_submit GL_OES_vertex_array_object  GL_KHR_texture_compression_astc_ldr ANDROID_EMU_host_side_tracing  ANDROID_EMU_async_frame_commands ANDROID_EMU_gles_max_version_2 
D/EGL_emulation( 6089): eglMakeCurrent: 0xe90561a0: ver 2 0 (tinfo  0xe0eadb70)
E/flutter ( 6089): [ERROR:flutter/lib/ui/ui_dart_state.cc(186)] Unhandled   Exception: NoSuchMethodError: The method 'split' was called on null. 
E/flutter ( 6089): Receiver: null
E/flutter ( 6089): Tried calling: split(":")
E/flutter ( 6089): #0      Object.noSuchMethod (dart:core- patch/object_patch.dart:54:5)
E/flutter ( 6089): #1      NotificationPlugin.showDailyAtTime (package:finance_manager/widgets/NotificationPlugin.dart:107:30)
E/flutter ( 6089): #2      callbackDispatcher.<anonymous closure> (package:finance_manager/main.dart:14:24)
E/flutter ( 6089): #3      callbackDispatcher.<anonymous closure> (package:finance_manager/main.dart:12:29)
E/flutter ( 6089): #4      Workmanager.executeTask.<anonymous closure> (package:workmanager/src/workmanager.dart:89:28)
E/flutter ( 6089): #5      Workmanager.executeTask.<anonymous closure> (package:workmanager/src/workmanager.dart:87:45)
E/flutter ( 6089): #6      MethodChannel._handleAsMethodCall (package:flutter/src/services/platform_channel.dart:435:55)
E/flutter ( 6089): #7      MethodChannel.setMethodCallHandler.<anonymous closure> (package:flutter/src/services/platform_channel.dart:382:34)
E/flutter ( 6089): #8      _DefaultBinaryMessenger.handlePlatformMessage (package:flutter/src/services/binding.dart:284:33)
E/flutter ( 6089): #9      _invoke3.<anonymous closure> (dart:ui/hooks.dart:221:15)
E/flutter ( 6089): #10     _rootRun (dart:async/zone.dart:1354:13)
E/flutter ( 6089): #11     _CustomZone.run (dart:async/zone.dart:1258:19)
E/flutter ( 6089): #12     _CustomZone.runGuarded (dart:async/zone.dart:1162:7)
E/flutter ( 6089): #13     _invoke3 (dart:ui/hooks.dart:220:10)
E/flutter ( 6089): #14     PlatformDispatcher._dispatchPlatformMessage (dart:ui/platform_dispatcher.dart:457:7)
E/flutter ( 6089): #15     _dispatchPlatformMessage (dart:ui/hooks.dart:90:31)
E/flutter ( 6089): 
I/WM-WorkerWrapper( 6089): Worker result SUCCESS for Work [ id=87272c98-d905-4b69-a1ce-86c13336ab8b, tags={ be.tramckrijte.workmanager.BackgroundWorker }  ]

请帮我。

感谢您提前回复。

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