Flutter event distribution

stay Other front-end development , To decouple Will use the event center , To distribute the event ; Flutter in You can also do this ;

But what? There is a market for plug-ins called   event_bus Of ; It doesn't feel very good ！

The place follows the previous train of thought ; Moved one ！

Reference resources ：https://www.jianshu.com/p/d036ed61f1c8 ; But it's probably an old version ;

This is optimized as follows ：

typedef void EventCallback(arg);

class AppEvent {
  static final AppEvent _instance = AppEvent._internal();
  AppEvent._internal();
  factory AppEvent() {
    return _instance;
  }
  // Save the event subscriber queue ,key: Event name (id),value:  Subscriber queue corresponding to the event 
  final _eMap = <dynamic, List<EventCallback>>{};

  // Add subscribers 
  void on(eventName, EventCallback callBack) {
    if (eventName == null) return;
    if (!_eMap.containsKey(eventName)) {
      _eMap.addEntries({eventName: <EventCallback>[]}.entries);
    }
    _eMap[eventName]?.add(callBack);
  }

  // Remove subscribers 
  void off(eventName, {EventCallback? callBack}) {
    var list = _eMap[eventName];
    if (eventName == null || list == null) return;
    if (callBack == null) {
      // _eMap[eventName] = null;
      _eMap[eventName]?.clear();
    } else {
      list.remove(callBack);
    }
  }

  // Triggering event , After the event is triggered, all subscribers of the event will be called 
  void emit(eventName, [arg]) {
    var list = _eMap[eventName];
    if (list == null) {
      print('** No corresponding subscription method found $eventName');
      return;
    }
    int len = list.length - 1;
    // Reverse traversal , Prevent subscribers from removing subscript misalignment caused by themselves in the callback 
    for (var i = len; i > -1; --i) {
      list[i](arg);
    }
  }
}

• Add listening ：

  AppEvent().on('pageReport-examine', (arg) {
    print('>>>>> Received a message $arg');
    setState(() {
      _examineListSelect.add(arg);
    });
  });

• Cancel monitoring ：

  AppEvent().off('pageReport-examine');

• Trigger function ：

  AppEvent().emit(
    'pageReport-examine',
    {
      'id': '110',
      'patrolRecordId': 'id',
      'routeSubId': 'id',
      'placeName': ' Test node ',
      'checkTime': '',
      'isChecked': false,
      'checkRecordInfo': {
        'trouble': false,
        'address': _locationResult?['address'],
        'longitude': _locationResult?['latitude'],
        'latitude': _locationResult?['longitude'],
        'imgs': _selectPicture,
        'voicePath': _selectAudio.isNotEmpty ? _selectAudio.first : '',
        'bak': '',
        'videoPath': _selectVideo.isNotEmpty ? _selectVideo.first : ''
      },
    },
  );