Reactive redux store for Dart & Flutter Redux implementation based on Dart Stream

rx_redux

• Reactive redux store for Dart & Flutter inspired by RxRedux-freeletics

• A Redux store implementation entirely based on Dart Stream, with the power of RxDart (inspired by redux-observable) that helps to isolate side effects. RxRedux is (kind of) a replacement for RxDart’s .scan() operator.

Get started

dependencies:
  rx_redux: ^2.0.0

How is this different from other Redux implementations

In contrast to any other Redux inspired library out there, this library is pure backed on top of Dart Stream. This library offers a custom stream transformer ReduxStoreStreamTransformer (or extension method reduxStore) and treats upstream events as Actions.

Basic concepts

Redux Store

• A Store is basically an stream container for state. This library offers a custom stream transformer ReduxStoreStreamTransformer (or extension method reduxStore) to create such a state container. It takes an initialState and a list of SideEffect<State, Action> and a Reducer<State, Action>.

• Since version 2.x, add RxReduxStore class, built for Flutter UI.

Action

An Action is a command to “do something” in the store. An Action can be triggered by the user of your app (i.e. UI interaction like clicking a button) but also a SideEffect can trigger actions. Every Action goes through the reducer. If an Action is not changing the state at all by the Reducer (because it’s handled as a side effect), just return the previous state. Furthermore, SideEffects can be registered for a certain type of Action.

Reducer

A Reducer is basically a function (State, Action) -> State that takes the current State and an Action to compute a new State. Every Action goes through the state reducer. If an Action is not changing the state at all by the Reducer (because it’s handled as a side effect), just return the previous state.

Side Effect

A Side Effect is a function of type (Stream<Action>, GetState<State>) -> Stream<Action>. So basically it’s Actions in and Actions out. You can think of a SideEffect as a use case in clean architecture: It should do just one job. Every SideEffect can trigger multiple Actions (remember it returns Stream<Action>) which go through the Reducer but can also trigger other SideEffects registered for the corresponding Action. An Action can also have a payload. For example, if you load some data from backend, you emit the loaded data as an Action like class DataLoadedAction { final Foo data; }. The mantra an Action is a command to do something is still true: in that case it means data is loaded, do with it “something”.t

GetState

Whenever a SideEffect needs to know the current State it can use GetState to grab the latest state from Redux Store. GetState is basically just a function () -> State to grab the latest State anytime you need it.

Usage

Version 2.x: Prefer to use RxReduxStore over ReduxStoreStreamTransformer, but have same concept as version 1.x

final store = RxReduxStore(
  initialState: ViewState([]),
  sideEffects: [addTodoEffect, removeTodoEffect, toggleTodoEffect],
  reducer: reducer,
  logger: rxReduxDefaultLogger,
);

store.stateStream.listen((event) => print('~> State : $event'));
store.actionStream.listen((event) => print('~> Action: $event'));
store.dispatch(Action(Todo(i, 'Title $i', i.isEven), ActionType.add));
await store.dispose();

Note: below is the documentation for version 1.x, but have same concept as version 2.x

Let’s create a simple Redux Store for Pagination: Goal is to display a list of Persons on screen. For a complete example check the sample application incl. README but for the sake of simplicity let’s stick with this simple “list of persons example”:

1. Define State and initialState

class State {
  final int currentPage;
  final List<Person> persons; // The list of persons 
  final bool loadingNextPage;
  final errorLoadingNextPage;
  // constructor
  // hashCode and ==
  // copyWith
}

final initialState = State(
  currentPage: 0, 
  persons: [], 
  loadingNextPage: false, 
  errorLoadingNextPage: null,
);

2. Define Actions

abstract class Action { }

// Action to load the first page. Triggered by the user.
class LoadNextPageAction implements Action {
  const LoadNextPageAction();
}

// Persons has been loaded
class PageLoadedAction implements Action {
  final List<Person> personsLoaded;
  final int page;
  // constructor
}

// Started loading the list of persons
class LoadPageAction implements Action {
  const LoadPageAction();
}

// An error occurred while loading
class ErrorLoadingNextPageAction implements Action {
  final error;
  // constructor
}

3. Define SideEffects

// SideEffect is just a type alias for such a function:
Stream<State> loadNextPageSideEffect (
  Stream<Action> actions,
  GetState<State> state,
) =>
  actions
    // This side effect only runs for actions of type LoadNextPageAction
    .whereType<LoadNextPageAction>()
    .switchMap((_) {
      // do network request
      final State currentState = state();
      final int nextPage = state.currentPage + 1;

      return backend
        .getPersons(nextPage)
        .map<Action>((List<Person> person) {
          return PageLoadedAction(
            personsLoaded: persons, 
            page: nextPage
          );
        })
        .onErrorReturnWith((error) => ErrorLoadingNextPageAction(error))
        .startWith(const LoadPageAction());
    });

4. Define Reducer

// Reducer is just a type alias for a function
State reducer(State state, Action action) {
  if (action is LoadPageAction) {
    return state.copyWith(loadingNextPage: true);
  }
  if (action is ErrorLoadingNextPageAction) {
    return state.copy(
      loadingNextPage: false,
      errorLoadingNextPage: action.error,
    );
  }
  if (action is PageLoadedAction) {
    return state.copy(
      loadingNextPage: false, 
      errorLoadingNextPage: null
      persons: [...state.persons, ...action.persons],
      page: action.page,
    );
  }

  // Reducer is actually not handling this action (a SideEffect does it)
  return state;
}

5. Combine all it into one

• Using ReduxStoreStreamTransformer:

final Stream<Action> actions = PublishSubject<Action>();
final List<SideEffect<State, Action> sideEffects = [loadNextPageSideEffect, ...];

actions.transform(
  ReduxStoreStreamTransformer<Action, State>(
    initialStateSupplier: () => initialState,
    sideEffects: sideEffects,
    reducer: reducer,
  ),
).listen(view.render);

• Using extension method reduxStore:

actions.reduxStore(
  initialStateSupplier: () => initialState,
  sideEffects: sideEffects,
  reducer: reducer,
).listen(view.render);

• Using RxReduxStore:

final store = RxReduxStore(
  initialState: initialState,
  sideEffects: sideEffects,
  reducer: reducer,
  logger: rxReduxDefaultLogger,
  errorHandler: (error, st) => print('$error, $st'),
);
store.stateStream.listen(view.render);

Action action = ...;
store.dispatch(action);

6. More details

The following video (click on it) illustrates the workflow:

0. Let’s take a look at the following illustration: The blue box is the View (think UI). The Presenter or ViewModel has not been drawn for the sake of readability but you can think of having such additional layers between View and Redux State Machine. The yellow box represents a Store. The grey box is the reducer. The pink box is a SideEffect Additionally, a green circle represents State and a red circle represents an Action (see next step). On the right you see a UI mock of a mobile app to illustrate UI changes.

1. NextPageAction gets triggered from the UI (by scrolling at the end of the list). Every Action goes through the reducer and all SideEffects registered for this type of Action.

2. Reducer is not interested in NextPageAction. So while NextPageAction goes through the reducer, it doesn’t change the state.

3. loadNextPageSideEffect (pink box), however, cares about NextPageAction. This is the trigger to run the side-effect.

4. So loadNextPageSideEffect takes NextPageAction and starts doing the job and makes the http request to load the next page from backend. Before doing that, this side effect starts with emitting LoadPageAction.

5. Reducer takes LoadPageAction emitted from the side effect and reacts on it by “reducing the state”. This means Reducer knows how to react on LoadPageAction to compute the new state (showing progress indicator at the bottom of the list). Please note that the state has changed (highlighted in green) which also results in changing the UI (progress indicator at the end of the list).

6. Once loadNextPageSideEffect gets the result back from backend, the side effect emits a new PageLoadedAction. This Action contains a “payload” - the loaded data.

class PageLoadedAction implements Action {
  final List<Person> personsLoaded;
  final int page;
}

7. As any other Action PageLoadedAction goes through the Reducer. The Reducer processes this Action and computes a new state out of it by appending the loaded data to the already existing data (progress bar also is hidden).

Final remark: This system allows you to create a plugin in system of SideEffects that are highly reusable and specific to do a single use case.

Also SideEffects can be invoked by Actions from other SideEffects.

For a complete example check the sample application incl. README

FAQ

I get a StackOverflowError

This is a common pitfall and is most of the time caused by the fact that a SideEffect emits an Action as output that it also consumes from upstream leading to an infinite loop.

final SideEffect<State, Int> sideEffect = (actions, state) => actions.map((i) => i * 2);

final inputActions = Stream.value(1);

inputActions.reduxStore(
  initialStateSupplier: () => 'InitialState',
  sideEffects: [sideEffect],
  reducer: (state, action) => newState,
);

The problem is that from upstream we get Int 1. But since SideEffect reacts on that action Int 1 too, it computes 1 * 2 and emits 2, which then again gets handled by the same SideEffect 2 * 2 = 4 and emits 4, which then again gets handled by the same SideEffect 4 * 2 = 8 and emits 8, which then getst handled by the same SideEffect and so on (endless loop) …

Who processes an Action first: Reducer or SideEffect

Since every Action runs through both Reducer and registered SideEffects this is a valid question. Technically speaking Reducer gets every Action from upstream before the registered SideEffects. The idea behind this is that a Reducer may have already changed the state before a SideEffect start processing the Action.

For example let’s assume upstream only emits exactly one Action (because then it’s simpler to illustrate the sequence of workflow):

// 1\. upstream emits events
final upstreamActions = Stream.value(SomeAction());

SideEffect<State, Action> sideEffect1 = (actions, state) {
  // 3\. Runs because of SomeAction
  return actions.where((a) => a is SomeAction).mapTo(OtherAction());
};

SideEffect<State, Action> sideEffect2 = (actions, state) {
  // 5\. Runs because of OtherAction
  return actions.where((a) => a is OtherAction).mapTo(YetAnotherAction());
};

upstreamActions.reduxStore(
  initialStateSupplier: () => initialState,
  sideEffects: [sideEffect1, sideEffect2],
  reducer: (state, action) {
    // 2\. This runs first because of SomeAction
    ...
    // 4\. This runs again because of OtherAction (emitted by SideEffect1)
    ...
    // 6\. This runs again because of YetAnotherAction emitted from SideEffect2)
  }
).listen(print);

So the workflow is as follows:

1. Upstream emits SomeAction
2. reducer processes SomeAction
3. SideEffect1 reacts on SomeAction and emits OtherAction as output
4. reducer processes OtherAction
5. SideEffect2 reacts on OtherAction and emits YetAnotherAction
6. reducer processes YetAnotherAction

Can I use variable and function for SideEffects or Reducer

Absolutely. SideEffect is just a type alias for a function typedef Stream<A> SideEffect<S, A>(Stream<A> actions, GetState<S> state);.

In Dart you can use a lambda for that like this:

SideEffect<State, Action> sideEffect1 = (actions, state) {
  return actions
      .where((a) => a is SomeAction)
      .mapTo(OtherAction());
};

of write a function (instead of a lambda):

Stream<Action> sideEffect2(
  Stream<Action> actions,
  GetState<State> state,
) {
  return actions
      .where((a) => a is SomeAction)
      .mapTo(OtherAction());
}

Both are totally equal and can be used like that:

upstreamActions.reduxStore(
  initialStateSupplier: () => initialState,
  sideEffects: [sideEffect1, sideEffect2],
  reducer: (state, action) => newState,
).listen(...);

The same is valid for Reducer. Reducer is just a type alias for a function typedef S Reducer<S, A>(S currentState, A newAction); You can define your reducer as lambda or function:

final reducer = (State state, Action action) => /*return new state*/;

// or

State reducer(State state, Action action) {
  // return new state
}

Is distinct (More commonly known as distinctUntilChanged in other Rx implementations) considered as best practice

Yes it is because reduxStore(...) is not taking care of only emitting state that has been changed compared to previous state. Therefore, .distinct() is considered as best practice.

actions
  .reduxStore( ... )
  .distinct()
  .listen(view.render);

What if I would like to have a SideEffect that returns no Action

For example, let’s say you just store something in a database, but you don’t need a Action as result piped backed to your redux store. In that case you can simple use Stream.empty() like this:

Stream<Action> saveToDatabaseSideEffect(Stream<Action> actions, GetState<State> getState) {
    return actions.flatMap((_) async* {
      await saveToDb(something);
      // not emit any Action
    });
}

How do I cancel ongoing SideEffects if a certain Action happens

Let’s assume you have a simple SideEffect that is triggered by Action1. Whenever Action2 is emitted our SideEffect should stop. In RxDart this is quite easy to do by using: .takeUntil()

mySideEffect(Stream<Action> actions, GetState<State> getState) => 
    actions
        .whereType<Action1>()
        .flatMap((_) => doSomething())
        .takeUntil(actions.whereType<Action2>()); // Once Action2 triggers the whole SideEffect gets canceled.

Do I need an Action to start observing data

Let’s say you would like to start observing a database right from the start inside your Store. This sounds pretty much like as soon as you have subscribers to your Store and therefore you don’t need a dedicated Action to start observing the database.

Stream<Action> observeDatabaseSideEffect(Stream<Action> _, GetState<State> __) =>
    database // please notice that we don't use Stream<Action> at all
        .queryItems()
        .map((items) => DatabaseLoadedAction(items));

Features and bugs

Please file feature requests and bugs at the issue tracker.

Download Details:

Author: hoc081098

Source Code: https://github.com/hoc081098/rx_redux

#react #reactjs #flutter #dart #mobile-apps

What is GEEK

Buddha Community

Google's Flutter 1.20 stable announced with new features - Navoki

Flutter Google cross-platform UI framework has released a new version 1.20 stable.

Flutter is Google’s UI framework to make apps for Android, iOS, Web, Windows, Mac, Linux, and Fuchsia OS. Since the last 2 years, the flutter Framework has already achieved popularity among mobile developers to develop Android and iOS apps. In the last few releases, Flutter also added the support of making web applications and desktop applications.

Last month they introduced the support of the Linux desktop app that can be distributed through Canonical Snap Store(Snapcraft), this enables the developers to publish there Linux desktop app for their users and publish on Snap Store.  If you want to learn how to Publish Flutter Desktop app in Snap Store that here is the tutorial.

Flutter 1.20 Framework is built on Google’s made Dart programming language that is a cross-platform language providing native performance, new UI widgets, and other more features for the developer usage.

Here are the few key points of this release:

Performance improvements for Flutter and Dart

In this release, they have got multiple performance improvements in the Dart language itself. A new improvement is to reduce the app size in the release versions of the app. Another performance improvement is to reduce junk in the display of app animation by using the warm-up phase.

If your app is junk information during the first run then the Skia Shading Language shader provides for pre-compilation as part of your app’s build. This can speed it up by more than 2x.

Added a better support of mouse cursors for web and desktop flutter app,. Now many widgets will show cursor on top of them or you can specify the type of supported cursor you want.

Autofill for mobile text fields

Autofill was already supported in native applications now its been added to the Flutter SDK. Now prefilled information stored by your OS can be used for autofill in the application. This feature will be available soon on the flutter web.

A new widget for interaction

InteractiveViewer is a new widget design for common interactions in your app like pan, zoom drag and drop for resizing the widget. Informations on this you can check more on this API documentation where you can try this widget on the DartPad. In this release, drag-drop has more features added like you can know precisely where the drop happened and get the position.

Updated Material Slider, RangeSlider, TimePicker, and DatePicker

In this new release, there are many pre-existing widgets that were updated to match the latest material guidelines, these updates include better interaction with Slider and RangeSlider, DatePicker with support for date range and time picker with the new style.

New pubspec.yaml format

Other than these widget updates there is some update within the project also like in pubspec.yaml file format. If you are a flutter plugin publisher then your old pubspec.yaml  is no longer supported to publish a plugin as the older format does not specify for which platform plugin you are making. All existing plugin will continue to work with flutter apps but you should make a plugin update as soon as possible.

Preview of embedded Dart DevTools in Visual Studio Code

Visual Studio code flutter extension got an update in this release. You get a preview of new features where you can analyze that Dev tools in your coding workspace. Enable this feature in your vs code by _dart.previewEmbeddedDevTools_setting. Dart DevTools menu you can choose your favorite page embed on your code workspace.

Network tracking

The updated the Dev tools comes with the network page that enables network profiling. You can track the timings and other information like status and content type of your** network calls** within your app. You can also monitor gRPC traffic.

Generate type-safe platform channels for platform interop

Pigeon is a command-line tool that will generate types of safe platform channels without adding additional dependencies. With this instead of manually matching method strings on platform channel and serializing arguments, you can invoke native class and pass nonprimitive data objects by directly calling the Dartmethod.

There is still a long list of updates in the new version of Flutter 1.2 that we cannot cover in this blog. You can get more details you can visit the official site to know more. Also, you can subscribe to the Navoki newsletter to get updates on these features and upcoming new updates and lessons. In upcoming new versions, we might see more new features and improvements.

You can get more free Flutter tutorials you can follow these courses:

• Setup Flutter Desktop on Windows, Linux, MacOS using VSCode and Build – Flutter Tutorial
• Flutter Desktop Linux app | Build and Publish on Snapcraft Store
• Firebase Local Emulator Suite in Flutter

#dart #developers #flutter #app developed #dart devtools in visual studio code #firebase local emulator suite in flutter #flutter autofill #flutter date picker #flutter desktop linux app build and publish on snapcraft store #flutter pigeon #flutter range slider #flutter slider #flutter time picker #flutter tutorial #flutter widget #google flutter #linux #navoki #pubspec format #setup flutter desktop on windows

What is Flutter and why you should learn it?

Flutter is an open-source UI toolkit for mobile developers, so they can use it to build native-looking** Android and iOS** applications from the same code base for both platforms. Flutter is also working to make Flutter apps for Web, PWA (progressive Web-App) and Desktop platform (Windows,macOS,Linux).

Flutter was officially released in December 2018. Since then, it has gone a much stronger flutter community.

There has been much increase in flutter developers, flutter packages, youtube tutorials, blogs, flutter examples apps, official and private events, and more. Flutter is now on top software repos based and trending on GitHub.

Flutter meaning?

What is Flutter? this question comes to many new developer’s mind.

Flutter means flying wings quickly, and lightly but obviously, this doesn’t apply in our SDK.

So Flutter was one of the companies that were acquired by **Google **for around $40 million. That company was based on providing gesture detection and recognition from a standard webcam. But later when the Flutter was going to release in alpha version for developer it’s name was Sky, but since Google already owned Flutter name, so they rename it to Flutter.

Where Flutter is used?

Flutter is used in many startup companies nowadays, and even some MNCs are also adopting Flutter as a mobile development framework. Many top famous companies are using their apps in Flutter. Some of them here are

Dream11

NuBank

Reflectly app

Abbey Road Studios

and many more other apps. Mobile development companies also adopted Flutter as a service for their clients. Even I was one of them who developed flutter apps as a freelancer and later as an IT company for mobile apps.

#dart #flutter #uncategorized #flutter framework #flutter jobs #flutter language #flutter meaning #flutter meaning in hindi #google flutter #how does flutter work #what is flutter

Reactive redux store for Dart & Flutter Redux implementation based on Dart Stream

rx_redux

• Reactive redux store for Dart & Flutter inspired by RxRedux-freeletics

• A Redux store implementation entirely based on Dart Stream, with the power of RxDart (inspired by redux-observable) that helps to isolate side effects. RxRedux is (kind of) a replacement for RxDart’s .scan() operator.

Get started

dependencies:
  rx_redux: ^2.0.0

How is this different from other Redux implementations

In contrast to any other Redux inspired library out there, this library is pure backed on top of Dart Stream. This library offers a custom stream transformer ReduxStoreStreamTransformer (or extension method reduxStore) and treats upstream events as Actions.

Basic concepts

Redux Store

• A Store is basically an stream container for state. This library offers a custom stream transformer ReduxStoreStreamTransformer (or extension method reduxStore) to create such a state container. It takes an initialState and a list of SideEffect<State, Action> and a Reducer<State, Action>.

• Since version 2.x, add RxReduxStore class, built for Flutter UI.

Action

An Action is a command to “do something” in the store. An Action can be triggered by the user of your app (i.e. UI interaction like clicking a button) but also a SideEffect can trigger actions. Every Action goes through the reducer. If an Action is not changing the state at all by the Reducer (because it’s handled as a side effect), just return the previous state. Furthermore, SideEffects can be registered for a certain type of Action.

Reducer

A Reducer is basically a function (State, Action) -> State that takes the current State and an Action to compute a new State. Every Action goes through the state reducer. If an Action is not changing the state at all by the Reducer (because it’s handled as a side effect), just return the previous state.

Side Effect

A Side Effect is a function of type (Stream<Action>, GetState<State>) -> Stream<Action>. So basically it’s Actions in and Actions out. You can think of a SideEffect as a use case in clean architecture: It should do just one job. Every SideEffect can trigger multiple Actions (remember it returns Stream<Action>) which go through the Reducer but can also trigger other SideEffects registered for the corresponding Action. An Action can also have a payload. For example, if you load some data from backend, you emit the loaded data as an Action like class DataLoadedAction { final Foo data; }. The mantra an Action is a command to do something is still true: in that case it means data is loaded, do with it “something”.t

GetState

Whenever a SideEffect needs to know the current State it can use GetState to grab the latest state from Redux Store. GetState is basically just a function () -> State to grab the latest State anytime you need it.

Usage

Version 2.x: Prefer to use RxReduxStore over ReduxStoreStreamTransformer, but have same concept as version 1.x

final store = RxReduxStore(
  initialState: ViewState([]),
  sideEffects: [addTodoEffect, removeTodoEffect, toggleTodoEffect],
  reducer: reducer,
  logger: rxReduxDefaultLogger,
);

store.stateStream.listen((event) => print('~> State : $event'));
store.actionStream.listen((event) => print('~> Action: $event'));
store.dispatch(Action(Todo(i, 'Title $i', i.isEven), ActionType.add));
await store.dispose();

Note: below is the documentation for version 1.x, but have same concept as version 2.x

Let’s create a simple Redux Store for Pagination: Goal is to display a list of Persons on screen. For a complete example check the sample application incl. README but for the sake of simplicity let’s stick with this simple “list of persons example”:

1. Define State and initialState

class State {
  final int currentPage;
  final List<Person> persons; // The list of persons 
  final bool loadingNextPage;
  final errorLoadingNextPage;
  // constructor
  // hashCode and ==
  // copyWith
}

final initialState = State(
  currentPage: 0, 
  persons: [], 
  loadingNextPage: false, 
  errorLoadingNextPage: null,
);

2. Define Actions

abstract class Action { }

// Action to load the first page. Triggered by the user.
class LoadNextPageAction implements Action {
  const LoadNextPageAction();
}

// Persons has been loaded
class PageLoadedAction implements Action {
  final List<Person> personsLoaded;
  final int page;
  // constructor
}

// Started loading the list of persons
class LoadPageAction implements Action {
  const LoadPageAction();
}

// An error occurred while loading
class ErrorLoadingNextPageAction implements Action {
  final error;
  // constructor
}

3. Define SideEffects

// SideEffect is just a type alias for such a function:
Stream<State> loadNextPageSideEffect (
  Stream<Action> actions,
  GetState<State> state,
) =>
  actions
    // This side effect only runs for actions of type LoadNextPageAction
    .whereType<LoadNextPageAction>()
    .switchMap((_) {
      // do network request
      final State currentState = state();
      final int nextPage = state.currentPage + 1;

      return backend
        .getPersons(nextPage)
        .map<Action>((List<Person> person) {
          return PageLoadedAction(
            personsLoaded: persons, 
            page: nextPage
          );
        })
        .onErrorReturnWith((error) => ErrorLoadingNextPageAction(error))
        .startWith(const LoadPageAction());
    });

4. Define Reducer

// Reducer is just a type alias for a function
State reducer(State state, Action action) {
  if (action is LoadPageAction) {
    return state.copyWith(loadingNextPage: true);
  }
  if (action is ErrorLoadingNextPageAction) {
    return state.copy(
      loadingNextPage: false,
      errorLoadingNextPage: action.error,
    );
  }
  if (action is PageLoadedAction) {
    return state.copy(
      loadingNextPage: false, 
      errorLoadingNextPage: null
      persons: [...state.persons, ...action.persons],
      page: action.page,
    );
  }

  // Reducer is actually not handling this action (a SideEffect does it)
  return state;
}

5. Combine all it into one

• Using ReduxStoreStreamTransformer:

final Stream<Action> actions = PublishSubject<Action>();
final List<SideEffect<State, Action> sideEffects = [loadNextPageSideEffect, ...];

actions.transform(
  ReduxStoreStreamTransformer<Action, State>(
    initialStateSupplier: () => initialState,
    sideEffects: sideEffects,
    reducer: reducer,
  ),
).listen(view.render);

• Using extension method reduxStore:

actions.reduxStore(
  initialStateSupplier: () => initialState,
  sideEffects: sideEffects,
  reducer: reducer,
).listen(view.render);

• Using RxReduxStore:

final store = RxReduxStore(
  initialState: initialState,
  sideEffects: sideEffects,
  reducer: reducer,
  logger: rxReduxDefaultLogger,
  errorHandler: (error, st) => print('$error, $st'),
);
store.stateStream.listen(view.render);

Action action = ...;
store.dispatch(action);

6. More details

The following video (click on it) illustrates the workflow:

0. Let’s take a look at the following illustration: The blue box is the View (think UI). The Presenter or ViewModel has not been drawn for the sake of readability but you can think of having such additional layers between View and Redux State Machine. The yellow box represents a Store. The grey box is the reducer. The pink box is a SideEffect Additionally, a green circle represents State and a red circle represents an Action (see next step). On the right you see a UI mock of a mobile app to illustrate UI changes.

1. NextPageAction gets triggered from the UI (by scrolling at the end of the list). Every Action goes through the reducer and all SideEffects registered for this type of Action.

2. Reducer is not interested in NextPageAction. So while NextPageAction goes through the reducer, it doesn’t change the state.

3. loadNextPageSideEffect (pink box), however, cares about NextPageAction. This is the trigger to run the side-effect.

4. So loadNextPageSideEffect takes NextPageAction and starts doing the job and makes the http request to load the next page from backend. Before doing that, this side effect starts with emitting LoadPageAction.

5. Reducer takes LoadPageAction emitted from the side effect and reacts on it by “reducing the state”. This means Reducer knows how to react on LoadPageAction to compute the new state (showing progress indicator at the bottom of the list). Please note that the state has changed (highlighted in green) which also results in changing the UI (progress indicator at the end of the list).

6. Once loadNextPageSideEffect gets the result back from backend, the side effect emits a new PageLoadedAction. This Action contains a “payload” - the loaded data.

class PageLoadedAction implements Action {
  final List<Person> personsLoaded;
  final int page;
}

7. As any other Action PageLoadedAction goes through the Reducer. The Reducer processes this Action and computes a new state out of it by appending the loaded data to the already existing data (progress bar also is hidden).

Final remark: This system allows you to create a plugin in system of SideEffects that are highly reusable and specific to do a single use case.

Also SideEffects can be invoked by Actions from other SideEffects.

For a complete example check the sample application incl. README

FAQ

I get a StackOverflowError

This is a common pitfall and is most of the time caused by the fact that a SideEffect emits an Action as output that it also consumes from upstream leading to an infinite loop.

final SideEffect<State, Int> sideEffect = (actions, state) => actions.map((i) => i * 2);

final inputActions = Stream.value(1);

inputActions.reduxStore(
  initialStateSupplier: () => 'InitialState',
  sideEffects: [sideEffect],
  reducer: (state, action) => newState,
);

The problem is that from upstream we get Int 1. But since SideEffect reacts on that action Int 1 too, it computes 1 * 2 and emits 2, which then again gets handled by the same SideEffect 2 * 2 = 4 and emits 4, which then again gets handled by the same SideEffect 4 * 2 = 8 and emits 8, which then getst handled by the same SideEffect and so on (endless loop) …

Who processes an Action first: Reducer or SideEffect

Since every Action runs through both Reducer and registered SideEffects this is a valid question. Technically speaking Reducer gets every Action from upstream before the registered SideEffects. The idea behind this is that a Reducer may have already changed the state before a SideEffect start processing the Action.

For example let’s assume upstream only emits exactly one Action (because then it’s simpler to illustrate the sequence of workflow):

// 1\. upstream emits events
final upstreamActions = Stream.value(SomeAction());

SideEffect<State, Action> sideEffect1 = (actions, state) {
  // 3\. Runs because of SomeAction
  return actions.where((a) => a is SomeAction).mapTo(OtherAction());
};

SideEffect<State, Action> sideEffect2 = (actions, state) {
  // 5\. Runs because of OtherAction
  return actions.where((a) => a is OtherAction).mapTo(YetAnotherAction());
};

upstreamActions.reduxStore(
  initialStateSupplier: () => initialState,
  sideEffects: [sideEffect1, sideEffect2],
  reducer: (state, action) {
    // 2\. This runs first because of SomeAction
    ...
    // 4\. This runs again because of OtherAction (emitted by SideEffect1)
    ...
    // 6\. This runs again because of YetAnotherAction emitted from SideEffect2)
  }
).listen(print);

So the workflow is as follows:

1. Upstream emits SomeAction
2. reducer processes SomeAction
3. SideEffect1 reacts on SomeAction and emits OtherAction as output
4. reducer processes OtherAction
5. SideEffect2 reacts on OtherAction and emits YetAnotherAction
6. reducer processes YetAnotherAction

Can I use variable and function for SideEffects or Reducer

Absolutely. SideEffect is just a type alias for a function typedef Stream<A> SideEffect<S, A>(Stream<A> actions, GetState<S> state);.

In Dart you can use a lambda for that like this:

SideEffect<State, Action> sideEffect1 = (actions, state) {
  return actions
      .where((a) => a is SomeAction)
      .mapTo(OtherAction());
};

of write a function (instead of a lambda):

Stream<Action> sideEffect2(
  Stream<Action> actions,
  GetState<State> state,
) {
  return actions
      .where((a) => a is SomeAction)
      .mapTo(OtherAction());
}

Both are totally equal and can be used like that:

upstreamActions.reduxStore(
  initialStateSupplier: () => initialState,
  sideEffects: [sideEffect1, sideEffect2],
  reducer: (state, action) => newState,
).listen(...);

The same is valid for Reducer. Reducer is just a type alias for a function typedef S Reducer<S, A>(S currentState, A newAction); You can define your reducer as lambda or function:

final reducer = (State state, Action action) => /*return new state*/;

// or

State reducer(State state, Action action) {
  // return new state
}

Is distinct (More commonly known as distinctUntilChanged in other Rx implementations) considered as best practice

Yes it is because reduxStore(...) is not taking care of only emitting state that has been changed compared to previous state. Therefore, .distinct() is considered as best practice.

actions
  .reduxStore( ... )
  .distinct()
  .listen(view.render);

What if I would like to have a SideEffect that returns no Action

For example, let’s say you just store something in a database, but you don’t need a Action as result piped backed to your redux store. In that case you can simple use Stream.empty() like this:

Stream<Action> saveToDatabaseSideEffect(Stream<Action> actions, GetState<State> getState) {
    return actions.flatMap((_) async* {
      await saveToDb(something);
      // not emit any Action
    });
}

How do I cancel ongoing SideEffects if a certain Action happens

Let’s assume you have a simple SideEffect that is triggered by Action1. Whenever Action2 is emitted our SideEffect should stop. In RxDart this is quite easy to do by using: .takeUntil()

mySideEffect(Stream<Action> actions, GetState<State> getState) => 
    actions
        .whereType<Action1>()
        .flatMap((_) => doSomething())
        .takeUntil(actions.whereType<Action2>()); // Once Action2 triggers the whole SideEffect gets canceled.

Do I need an Action to start observing data

Let’s say you would like to start observing a database right from the start inside your Store. This sounds pretty much like as soon as you have subscribers to your Store and therefore you don’t need a dedicated Action to start observing the database.

Stream<Action> observeDatabaseSideEffect(Stream<Action> _, GetState<State> __) =>
    database // please notice that we don't use Stream<Action> at all
        .queryItems()
        .map((items) => DatabaseLoadedAction(items));

Features and bugs

Please file feature requests and bugs at the issue tracker.

Download Details:

Author: hoc081098

Source Code: https://github.com/hoc081098/rx_redux

#react #reactjs #flutter #dart #mobile-apps

Adobe XD plugin for Flutter with CodePen Tutorial

Recently Adobe XD releases a new version of the plugin that you can use to export designs directly into flutter widgets or screens. Yes, you read it right, now you can make and export your favorite design in Adobe XD and export all the design in the widget form or as a full-screen design, this can save you a lot of time required in designing.

What we will do?
I will make a simple design of a dialogue box with a card design with text over it as shown below. After you complete this exercise you can experiment with the UI. You can make your own components or import UI kits available with the Adobe XD.

#developers #flutter #adobe xd design export to flutter #adobe xd flutter code #adobe xd flutter code generator - plugin #adobe xd flutter plugin #adobe xd flutter plugin tutorial #adobe xd plugins #adobe xd to flutter #adobe xd tutorial #codepen for flutter.

6 Things About HTTP Request in Dart For Beginners

Introduction

If you are here and a beginner, that means you want to learn everything about making an API request using Dart in Flutter, then you are in the right place for the HTTP tutorial. So without wasting any time, let’s start with this flutter tutorial. We will cover the essential topics required to work with the HTTP request in Dart.

What is Rest API in Dart ?

Rest APIs are a way to fetch data from the internet in flutter or communicate the server from the app and get some essential information from your server to the app. This information can be regarding your app’s data, user’s data, or any data you want to share globally from your app to all of your users.

This HTTP request fetches in a unique JSON format, and then the information is fetched from the JSON and put in the UI of the app.

Every programming language has a way of some internet connectivity i.e, use this rest API developed on the server and fetch data from the internet. To use this request feature, we have to add HTTP package in flutter, add this flutter package add in your project to use the http feature. Add this HTTP package to your pubspec.yaml, and run a command in terminal :

flutter packages get

#dart #flutter #async await #async function #cancel http api request in flutter #fetch data from the internet #flutter cancel future #flutter get request example #flutter post request example #future of flutter #http tutorial