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.

  • prevState = 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.

  • newState = 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(prevState, newState);

  • 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 prevState and newState will be the current store state when the error was 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 prevState, AppState newState) { // Don't to anything }
}

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

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

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

Constructors

StateObserver()

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

  • action = The action itself.

  • prevState = 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.

  • newState = 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(prevState, newState);

  • 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 prevState and newState will be the current store state when the error was thrown.

  • dispatchCount = The sequential number of the dispatch.

    • toString() → String
    A string representation of this object.
    inherited

    Operators

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