manager #

A dart package for predictable synchronous and asynchronous state management with an effective approach. Inspired by BLoC pattern, adapted for asynchronous state management.

Overview #

Task #

A structure that represents a mutation operation applied to Manager.run. id is used to distinguish one task from another while being tracked by Manager.

There are 2 types of tasks that can be run by the managers:

• SynchronousTask. A type of Task that changes the state instantly by its return value. Manager emits only TaskSuccessEvent when an instance of this type is run.
• AsynchronousTask. A type of Task that changes the state if its future completes without an error. Manager emits TaskEvents in following order when an instance of this type is run:

  1. TaskLoadingEvent

  2. (If it completed without an error) TaskSuccessEvent

     (If completed with an error) TaskErrorEvent

CancelableAsyncTaskMixin #

It is a special mixin of AsynchronousTask that can be killed by Manager which triggers Manager to emit TaskKillEvent.

manager.killById('id_of_task');

Manager #

An event-driven structure that has the single state of a generic type.

State changes are encapsulated and only possible to be changed internally by calling mutateState or by running a Task via run method.

Key features and advantages:

• Every single attempt to change the state has its id and will be tracked.
• The manager allows running multiple AsynchronousTasks concurrently and track progress progress of them through on method.
• It is possible to filter and listen to incoming TaskEvents through on method by a type of a Task or by Task.id. - If you run a Task and manager already has a task with the same id - the previous task will be dismissed. So you don't need to worry about unwanted outcomes.
• An each Task that was completed with TaskSuccessEvent will change the state through mutateState.
• You can track an every state change by listening to onStateChanged

class CounterManager extends Manager<int> {
 CounterManager(super.initialValue);

 // changes the state instantly
 void incrementSync() =>
     run(SynchronousTask.generic(id: 'increment', result: state + 1));

 // Changes the state after 2 seconds
 void decrementAsync() => run(
       AsynchronousTask.generic(
         id: 'decrement',
         computation: () =>
             Future.delayed(const Duration(seconds: 2), () => state - 1),
       ),
     );
  
  // Will not change the state.
  void decrementAsyncError() => run(
       AsynchronousTask.generic(
         id: 'decrement',
         computation: () async {
           await Future.delayed(const Duration(seconds: 2));
           throw Exception('Exception');
         },
       ),
     );
}

Running tasks #

Note: Running the same AsynchronousTask (with same id) when the previous one hasn't been completed will dismiss the previous one and run the new one.

// Creating a manager
final manager = CounterManager(0);

// Syncronous tasks change manager's state immediately and TaskSuccessEvent is added to the manager
manager.incrementSync();

// prints 1
print(manager.state);

// Running the asynchronous tasks multiple times when the previous ones have not been completed WON'T change the state multiple times but dismiss the previous ones.
manager.decrementAsync();
manager.decrementAsync();
manager.decrementAsync();

await Future.delayed(const Duration(seconds: 2));

// prints 0
print(manager.state);

// If tasks are completed with an error, it will not affect the state
manager.decrementAsyncError();

await Future.delayed(const Duration(seconds: 2));

// prints 0
prints(manager.state);

Listening for events #

Manager exposes 2 stream methods:

• onStateChanged - emits a value of a manager's updated state.
• on - emits an instance of TaskEvent.

It's recommended to extend the AsynchronousTask or SynchronousTask rather than using the generic factory constructors of the classes to achieve a better semantics with on stream of Manager:

class AsynDecrementTask extends AsynchronousTask<int> {
  final CounterManager manager;

  AsynDecrementTask({required this.manager});

  @override
  String get id => 'counter_async_task';

  @override
  Future<int> run() async {
    await Future.delayed(const Duration(seconds: 2));
    return manager.state - 1;
  }
}

class SyncIncrementTask extends SynchronousTask<int> {
  final CounterManager manager;

  SyncIncrementTask({required this.manager});

  @override
  String get id => 'counter_sync_task';

  @override
  int run() => manager.state + 1;
}

class CounterManager extends Manager<int> {
  CounterManager(super.initialValue);

  void incrementSync() => run(SyncIncrementTask(manager: this));

  void decrementAsync() => run(AsynDecrementTask(manager: this));
}

void main(){
  // Listening for events of a specific task by type
  manager.on<SyncIncrementTask>().listen((event){});
  // Listening for events of a specific task by id
  manager.on(taskId: 'increment').listen((event){});
  // Listening for the state changes
  manager.onStateChanged().listen((state){});
}

Observers and observables #

Managers that extend ObservableManagerMixin can register ManagerObservers.

ManagerObserver #

A structure that can observe multiple managers. Observers can process the following lifecycle events of a manager:

• onCreated - When a manager is created.
• onDisposed - When a manager is disposed.
• onEvent - When an event fired in a manager.
• onStateMutated - When the state of a manager has been mutated.

Due to a feature that enables an instance of ManagerObserver to observe multiple managers of different types, use the following helper methods to utilize type checks.

• ManagerObserver.doIfValueIs
• ManagerObserver.doOnStateMutatedIfValuesAre
• ManagerObserver.doIfManagerIs
• ManagerObserver.doIfEventIs
• ManagerObserver.doIfTaskIs

class AsynDecrementTask extends AsynchronousTask<int> {
  final CounterManager manager;

  AsynDecrementTask({required this.manager});

  @override
  String get id => 'counter_async_task';

  @override
  Future<int> run() async {
    await Future.delayed(const Duration(seconds: 2));
    return manager.state - 1;
  }
}

class SyncIncrementTask extends SynchronousTask<int> {
  final CounterManager manager;

  SyncIncrementTask({required this.manager});

  @override
  String get id => 'counter_sync_task';

  @override
  int run() => manager.state + 1;
}

class SuccesCounterObserver extends ManagerObserver {
  int _internalSuccessCount = 0;

  int get successEventsCount => _internalSuccessCount;

  @override
  void onEvent(Manager manager, TaskEvent event) {
    ManagerObserver.doIfManagerIs<CounterManager>(manager, (_) {
      ManagerObserver.doIfEventIs<TaskSuccessEvent>(event, (_) {
        _internalSuccessCount++;
      });
    });
  }
}

class EventQueueDisplayObserver extends ManagerObserver {
  final eventQueue = <Type>[];

  @override
  void onEvent(Manager manager, TaskEvent event) {
    ManagerObserver.doIfManagerIs<CounterManager>(manager, (_) {
      eventQueue.add(event.runtimeType);
    });
  }
}

class CounterManager extends Manager<int>
    with ObservableManagerMixin {
  CounterManager(super.initialValue);
}


void main() async {
  // Creating a manager
  final manager = CounterManager(0);

  // Adding the observer to count all success events
  final successCountObserver = SuccesCounterObserver();
  manager.addObserver(successCountObserver);

  // Adding the observer to print a list of orders
  final eventQueueObserver = EventQueueDisplayObserver();
  manager.addObserver(eventQueueObserver);

  manager.run(AsynDecrementTask(manager: manager));
  manager.run(SyncIncrementTask(manager: manager));

  await Future.delayed(const Duration(seconds: 2));
   // prints [TaskLoadingEvent<int>, TaskSuccessEvent<int>, TaskSuccessEvent<int>,]
  print(eventQueueObserver.eventQueue);
  // prints 2
  print(successCountObserver.successEventsCount);

  // removing observers
  manager.removeObserver(eventQueueObserver);
  manager.removeObserver(successCountObserver);
}