QueryObserver class abstract

A BlocObserver specialised for query and mutation controllers.

Since QueryController, InfiniteQueryController, and MutationController all extend Cubit, the standard BlocObserver already fires for them automatically. QueryObserver filters those events and re-exposes them as typed, cache-key–aware hooks so you don't have to downcast BlocBase in your own observer.

Registration

// main.dart
QueryClient.instance.setObserver(AppQueryObserver());

Usage

class AppQueryObserver extends QueryObserver {
  @override
  void onQueryCreate(String cacheKey) =>
      debugPrint('Controller created: $cacheKey');

  @override
  void onQueryChange(
    String cacheKey,
    QueryState<dynamic> currentState,
    QueryState<dynamic> nextState,
  ) {
    debugPrint('[$cacheKey] ${currentState.status} → ${nextState.status}');
  }

  @override
  void onQueryError(String cacheKey, Object error, StackTrace stackTrace) =>
      FirebaseCrashlytics.instance.recordError(error, stackTrace);

  @override
  void onQueryClose(String cacheKey) =>
      debugPrint('Controller closed: $cacheKey');
}

Non-query cubits

You can still handle non-query cubits by overriding the raw BlocObserver hooks. Always call super to preserve query-specific behaviour:

@override
void onChange(BlocBase<dynamic> bloc, Change<dynamic> change) {
  super.onChange(bloc, change); // ← fires onQueryChange for query controllers
  if (bloc is MyOtherCubit) { ... }
}

Constructors

QueryObserver(): const

Properties

hashCode → int: The hash code for this object.
no setterinherited
runtimeType → Type: A representation of the runtime type of the object.
no setterinherited

Methods

noSuchMethod(Invocation invocation) → dynamic: Invoked when a nonexistent method or property is accessed.
inherited
onChange(BlocBase bloc, Change change) → void: Called whenever a Change occurs in any bloc A change occurs when a new state is emitted. onChange is called before a bloc's state has been updated.
onClose(BlocBase bloc) → void: Called whenever a Bloc is closed. onClose is called just before the Bloc is closed and indicates that the particular instance will no longer emit new states.
onCreate(BlocBase bloc) → void: Called whenever a Bloc is instantiated. In many cases, a cubit may be lazily instantiated and onCreate can be used to observe exactly when the cubit instance is created.
onDone(Bloc bloc, Object? event, [Object? error, StackTrace? stackTrace]) → void: Called whenever an event handler for a specific bloc has completed. This may include an error and stackTrace if an uncaught exception occurred within the event handler.
inherited
onError(BlocBase bloc, Object error, StackTrace stackTrace) → void: Called whenever an error is thrown in any Bloc or Cubit. The stackTrace argument may be StackTrace.empty if an error was received without a stack trace.
onEvent(Bloc bloc, Object? event) → void: Called whenever an event is added to any bloc with the given bloc and event.
inherited
onQueryChange(String cacheKey, QueryState currentState, QueryState nextState) → void: Called on every state change for a query or mutation controller.
onQueryClose(String cacheKey) → void: Called when a QueryController, InfiniteQueryController, or MutationController is closed.
onQueryCreate(String cacheKey) → void: Called when a QueryController, InfiniteQueryController, or MutationController is first created.
onQueryError(String cacheKey, Object error, StackTrace stackTrace) → void: Called when a query or mutation controller encounters an unhandled stream error.
onTransition(Bloc bloc, Transition transition) → void: Called whenever a transition occurs in any bloc with the given bloc and transition. A transition occurs when a new event is added and a new state is emitted from a corresponding EventHandler. onTransition is called before a bloc's state has been updated.
inherited
toString() → String: A string representation of this object.
inherited

Operators

operator ==(Object other) → bool: The equality operator.
inherited