applyMiddleware

StoreEnhancer<S> applyMiddleware<S>(

  1. List<Middleware<S>> middlewares

)

Applies middleware to the dispatch method of the store.

Middleware is the suggested way to extend functionality with custom behavior. It provides a third-party extension point between dispatching an action and the moment it reaches the reducer.

The middleware signature is:

Middleware<AppState> loggerMiddleware() => (api) => (next) => (action) {
  print('Dispatching: ${action.type}');
  next(action);
  print('Next state: ${api.getState()}');
};

final store = createStore(
reducer,
initialState,
enhancer: applyMiddleware([loggerMiddleware()]),
);

Implementation

StoreEnhancer<S> applyMiddleware<S>(List<Middleware<S>> middlewares) =>
    (createStoreFn, reducer, preloadedState) {
      final store = createStoreFn(reducer, preloadedState);

if (middlewares.isEmpty) return store;


// Create a dispatch that throws if called during middleware setup
NextDispatcher dispatch = _throwingDispatch;


final middlewareApi = (
getState: store.getState,
dispatch: (Action action) => dispatch(action),
);


// Build the middleware chain
final chain = middlewares.map((m) => m(middlewareApi)).toList();


// Compose the chain with the store's dispatch
dispatch = _composeMiddleware(chain)(store.dispatch);


return _MiddlewareStore(store, dispatch);
};