re-dash

A ClojureDart framework, inspired by re-frame, for building user interfaces with Flutter

Features

• Global central state management
• Pure views with no direct reference to global state
• Interact with global state via events & subscriptions
• Handle side effects at the edge with effect handlers
• Familiar api if coming from re-frame
  • Event Dispatch
  • Event Handling
    • Coeffects
    • Interceptors
  • Effect Handling
  • Signal Graph
  • Subscriptions

Documentation

Most (not all) of the concepts in re-frame has been made available in this library, and the aim is to share the same api as far as possible, so if you're familiar with re-frame, picking up re-dash should feel natural.

To gain an understanding of the concepts in re-dash, head over to the excellent documentation in re-frame

Also see State management in ClojureDart by Etienne Théodore for a detailed walk-through

Configuration

Follow the ClojureDart Quickstart guide to get your app up and running

Then, add the re-dash dependency

deps.edn

from clojars

:deps {net.clojars.htihospitality/re-dash {:mvn/version "0.8.1"}}

from a commit

:deps {hti/re-dash
       {:git/url "https://github.com/htihospitality/re-dash.git"
        :sha "find the latest sha on github"}}

Samples

• samples/counter Shows an example of an incrementing counter when clicked
• samples/fetch Shows an example of data fetching from an http endpoint, using effects
• samples/signals Same as 'samples/counter' but showing various subscription signals: single, vector & map
• samples/coeffects Shows an example of injecting coeffects into an event handler
• samples/local_storage Shows an example of how to initialize shared_preferences and inject values into event handlers using coeffects

Quickstart

What follows is an example of the six dominoes principle implemented with re-dash

The full working example is available under samples/counter

1st Domino - Event Dispatch

(ns acme.view
  (:require ["package:flutter/material.dart" :as m]
            [acme.model :as model]
            [hti.re-dash :as rd]))

...

(m/IconButton
 .icon (m/Icon (m/Icons.add_circle_outline))
 .onPressed #(rd/dispatch [::model/count]))    ;; <== This

...

More info

2nd Domino - Event Handling

Both reg-event-db and reg-event-fx are supported

(ns acme.model
  (:require [hti.re-dash :as rd]))

...

(rd/reg-event-fx
   ::count
   (fn [{:keys [db]} _]
     (let [current-count ((fnil inc 0) (:current-count db))]
       {:db (assoc db :current-count current-count)
        ::log-count current-count})))

...

More info

3rd Domino - Effect Handling

(ns acme.model
  (:require [hti.re-dash :as rd]))

...

(rd/reg-fx
   ::log-count
   (fn [current-count]
     (println (str "The current-count is " current-count))))

...

Built-in effects: :db :fx :dispatch dispatch-later :deregister-event-handler

Tip: Need to fetch some data? Do it here then dispatch a new event passing the response.

More info

4th Domino - Query

Subscribe to derived state, internally using ClojureDart Cells (see the Cheatsheet)

(ns acme.view
  (:require ["package:flutter/material.dart" :as m]
            [acme.model :as model]
            [hti.re-dash :as rd]))

...

(f/widget
 :watch [current-count (rd/subscribe [::model/get-count])]  ;; <== This
 (m/Text (str current-count)))
...

This example assumes a subscription called get-count has been pre-registered in the model.

• See samples/counter for a full example of registering the subscription.
• See samples/signals for more examples of registering subscriptions using extractors and/or signals.
• Also see re-frame subscriptions for a more detailed description.
• Note that the re-frame shorthand syntactic sugar is also supported.

More Info

5th Domino - View

Pure. No reference to global state.

(ns acme.view
  (:require ["package:flutter/material.dart" :as m]
            [cljd.flutter :as f]
            [acme.model :as model]
            [hti.re-dash :as rd]))

(def counter
  (m/Column
   .mainAxisAlignment m/MainAxisAlignment.center
   .children
   [(f/widget
     :watch [current-count (rd/subscribe [::model/get-count])]
     (m/Text (str current-count)))
    (m/IconButton
     .icon (m/Icon (m/Icons.add_circle_outline))
     .onPressed #(rd/dispatch [::model/count]))
    (m/Text "Click me to count!")]))

More info

Note, this is a contrived example to illustrate usage of this library. Best practice for when state remains local to the widget (for example key presses in a text field) should be handled in a local atom for example:

(ns acme.view
  (:require ["package:flutter/material.dart" :as m]
            [cljd.flutter :as f]
            [acme.model :as model]
            [hti.re-dash :as rd]))

(def counter
  (f/widget
   :watch [current-count (atom 0)]
   (m/Column
    .mainAxisAlignment m/MainAxisAlignment.center
    .children
    [(m/Text (str current-count))
     (m/IconButton
      .icon (m/Icon (m/Icons.add_circle_outline))
      .onPressed #(swap! current-count inc))
     (m/Text "Click me to count!")])))

6th Domino - Canvas

Done.

More info

Registering events, effects & subscriptions

Unfortunately, due to the Dart compiler's tree shaking of unused code, it incorrectly removes events, effects & subscriptions if declared at the root of a ClojureDart name space. To work around this, we need to wrap all the registrations inside a function callable from main so the Dart compiler sees there is a reference to the code

(ns acme.main
  (:require ["package:flutter/material.dart" :as m]
            [cljd.flutter :as f]
            [acme.view :as view]
            [acme.model :as model]))

(defn main []
  (model/register!)                     ;; <== This
  (f/run
    (m/MaterialApp
     .title "Welcome to Flutter"
     .theme (m/ThemeData .primarySwatch m.Colors/blue))
    .home
    (m/Scaffold
     .appBar (m/AppBar
              .title (m/Text "ClojureDart with a splash of re-dash")))
    .body
    m/Center
    view/counter))

and in the model

(ns acme.model
  (:require [hti.re-dash :as rd]))

(defn register!                         ;; <== This
  []

  (rd/reg-sub
   ::get-count
   (fn [db _]
     (:current-count db)))

  (rd/reg-fx
   ::log-count
   (fn [current-count]
     (println (str "The current-count is " current-count)))))

This does come with a drawback, as whenever we make a change in the model name space, hot reload does not pick up the changes, so a hot restart is needed instead. Note this only affect our model name space, hot reload works fine in our view. Maybe there is a way to keep our event registrations from being tree shaken, if so, we'd love to hear it!

Debugging

To debug our event handlers, we can register interceptors to automatically log when events fire, and how the app state db looked before and after the event.

See: debugging

Testing

re-dash comes with some utilities to help with writing tests

Fixtures

hti.re-dash-testing/reset-app-db-fixture can be used to reset / empty the app-db before and after tests

Subscriptions

Normally subscriptions are not able to be de-referenced outside a reactive context (like within tests)

Use hti.re-dash-testing/subscribe instead inside your tests if you need to assert a subscription's value (only layer 2 - extractors currently supported)

Events

When dispatching events from tests and you need to assert that app-db contains the expected updated state with a subscription, use

(await (dispatch-sync [:some-event-id]))

see the hti.re-dash-test namespace for example usage

Extra Features

reg-sub-as-cofx

Normally we wouldn't use subscriptions inside event handlers, see more info but in re-dash we have the ability to inject a subscription into an event handler as a coeffect

We do this by registering an existing subscription also as a coeffect with

(hti.re-dash/reg-sub-as-cofx [::existing-sub-id])

Now we can inject this subscription as a coeffect into an event handler

(rd/reg-event-fx
  ::some-event
  [(rd/inject-cofx ::existing-sub-id)]
  (fn [{db :db ::keys [existing-sub-id] :as cofx} _]
      ...))

Issues and features

Please feel free to raise issues on Github or send pull requests

Acknowledgements

• ClojureDart for the language
• re-frame for the inspiration for this library
• Dash the mascot for Dart & Flutter

Development

This section is a guide to developing this re-dash library itself

Prerequisites

Clojure and Flutter installed and on your path

Workflow

Fork, then clone this repository to a local folder like ~/src/re-dash

If you don't already have a ClojureDart/re-dash project you can copy one of the sample projects to start hacking:

cp -r ~/src/re-dash/samples/counter ~/src/counter

Add the re-dash src folder and remove the re-dash dependency from ~/src/counter/deps.edn

{:paths ["src" "../re-dash/src"]
 :deps {tensegritics/clojuredart
        {:git/url "https://github.com/tensegritics/ClojureDart.git"
         :sha "some sha"}}
 :aliases {:cljd {:main-opts ["-m" "cljd.build"]}}
 :cljd/opts {:kind :flutter
             :main acme.main}}

Create the platform folders and run the counter app

cd ~/src/counter

flutter create .

clj -M:cljd flutter -d linux  ;; or whichever device you want to run on

Now any changes you make in the re-dash source code will be picked up in the running counter app when doing a hot restart with 'R' in the terminal

Tests

re-dash tests are run like this

cd ~/src/re-dash

## first compile the test namespace

clj -M:cljd:test compile hti.re-dash-test

## run the tests

flutter test

License

MIT License

Copyright (c) 2023 Hospitality Technology Limited

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.