StateObserver<St> class abstract

One or more StateObservers can be set during the Store creation. Those observers are called for all dispatched actions, right after the reducer returns. That happens before the after() method is called, and before the action's wrapError() and the global wrapError() methods are called.

The parameters are:

• action = The action itself.

• stateIni = The state right before the new state returned by the reducer is applied. Note this may be different from the state when the reducer was called.

• stateEnd = The state returned by the reducer. Note: If you need to know if the state was changed or not by the reducer, you can compare both states: bool ifStateChanged = !identical(stateIni, stateEnd);

• error = Is null if the reducer completed with no error and returned. Otherwise, will be the error thrown by the reducer (before any wrapError is applied). Note that, in case of error, both stateIni and stateEnd will be the current store state when the error is thrown.

• dispatchCount = The sequential number of the dispatch.

Among other uses, the state-observer is a good place to add METRICS to your application. For example:

abstract class AppAction extends ReduxAction<AppState> {
  void trackEvent(AppState stateIni, AppState stateEnd) { // Don't to anything }
}

class AppStateObserver implements StateObserver<AppState> {
  @override
  void observe(
    ReduxAction<AppState> action,
    AppState stateIni,
    AppState stateEnd,
    Object? error,
    int dispatchCount,
  ) {
    if (action is AppAction) action.trackEvent(stateIni, stateEnd, error);
  }
}

class MyAction extends AppAction {
   @override
   AppState? reduce() { // Do something }

   @override
   void trackEvent(AppState stateIni, AppState stateEnd, Object? error) =>
      MyMetrics().track(this, stateEnd, error);
}

Constructors

StateObserver()

Properties

hashCode → int

The hash code for this object.

no setter, inherited

runtimeType → Type

A representation of the runtime type of the object.

no setter, inherited

Methods

noSuchMethod(Invocation invocation) → dynamic

Invoked when a nonexistent method or property is accessed.

inherited

observe(ReduxAction<St> action, St stateIni, St stateEnd, Object? error, int dispatchCount) → void

toString() → String

A string representation of this object.

inherited

Operators

operator ==(Object other) → bool

The equality operator.

inherited