react-dnd-multi-backend

React DnD Multi Backend

Try it here!

This project is a Drag'n'Drop backend compatible with React DnD. It enables your application to use different DnD backends depending on the situation. You can either generate your own backend pipeline or use the default one (HTML5toTouch).

HTML5toTouch starts by using the React DnD HTML5 Backend, but switches to the React DnD Touch Backend if a touch event is triggered. You application can smoothly use the nice HTML5 compatible backend and fallback on the Touch one on mobile devices!

Moreover, because some backends don't support preview, a Preview component has been added to make it easier to mock the Drag'n'Drop "ghost".

See the migration section for instructions when switching from react-dnd-multi-backend@2.x.x or react-dnd-multi-backend@3.1.2.

Installation

NPM Installation

npm install react-dnd-multi-backend

You can then MultiBackend = require('react-dnd-multi-backend') or import MultiBackend from 'react-dnd-multi-backend'. To get the HTML5toTouch pipeline, just require/import react-dnd-multi-backend/lib/HTML5toTouch.

Browser Installation

Use the minified UMD build in the dist folder: here. It exports a global window.ReactDnDMultiBackend when imported as a <script> tag.

If you want to use the HTML5toTouch pipeline, also include RDMBHTML5toTouch.min.js. It exports a global window.RDMBHTML5toTouch when imported as a <script> tag. This file also includes the HTML5 and Touch backends, so no need to include them as well.

Usage

Backend

You can plug this backend in the DragDropContext the same way you do for any backend (e.g. ReactDnDHTML5Backend), you can see the docs for more information.

You must pass a 'pipeline' to use as argument. This package includes HTML5toTouch, but you can write your own. Note that if you include this file, you will have to add react-dnd-html5-backend and react-dnd-touch-backend to your package.json dependencies.

import { DndProvider } from 'react-dnd';
import MultiBackend from 'react-dnd-multi-backend';
import HTML5toTouch from 'react-dnd-multi-backend/lib/HTML5toTouch'; // or any other pipeline
...
function App() {
  return (
    <DndProvider backend={MultiBackend} options={HTML5toTouch}>
      <Example />
    </DndProvider>
  );
}

Create a custom pipeline

Creating a pipeline is fairly easy. A pipeline is composed of a list of backends, the first one will be the default one, loaded at the start of the MultiBackend, the order of the rest isn't important.

Each backend entry must specify one property: backend, containing the class of the Backend to instantiate. But other options are available:

• preview (a boolean indicating if Preview components should be shown)
• transition (an object returned by the createTransition function)
• skipDispatchOnTransition (a boolean indicating transition events should not be dispatched to new backend, defaults to false. See note below for details and use cases.)

Here is the HTML5toTouch pipeline code as an example:

...
import HTML5Backend from 'react-dnd-html5-backend';
import TouchBackend from 'react-dnd-touch-backend';
import MultiBackend, { TouchTransition } from 'react-dnd-multi-backend';
...
const HTML5toTouch = {
  backends: [
    {
      backend: HTML5Backend
    },
    {
      backend: TouchBackend({enableMouseEvents: true}), // Note that you can call your backends with options
      preview: true,
      transition: TouchTransition
    }
  ]
};
...
function App() {
  return (
    <DndProvider backend={MultiBackend} options={HTML5toTouch}>
      <Example />
    </DndProvider>
  );
}

TouchTransition is a predefined transition that you can use in your own pipelines, it is triggered when a touchstart is received. Transitions rea really easy to write, here is an example:

import { createTransition } from 'react-dnd-multi-backend';

const TouchTransition = createTransition('touchstart', (event) => {
  return event.touches != null;
});

You can also import HTML5DragTransition which works the same way, but detects when a HTML5 DragEvent is received.

Note on skipDispatchOnTransition

By default, when an event triggers a transition, dnd-multi-backend dispatches a cloned version of the event after setting up the new backend. This allows the newly activated backend to handle the original event.

If your app code or another library has registered event listeners for the same events that are being used for transitions, this duplicate event may cause problems.

You can optionally disable this behavior per backend:

const CustomHTML5toTouch = {
  backends: [
    {
      backend: HTML5Backend,
      transition: MouseTransition
      // by default, will dispatch a duplicate `mousedown` event when this backend is activated
    },
    {
      backend: TouchBackend,
      // Note that you can call your backends with options
      options: {enableMouseEvents: true},
      preview: true,
      transition: TouchTransition,
      // will not dispatch a duplicate `touchstart` event when this backend is activated
      skipDispatchOnTransition: true
    }
  ]
};

WARNING: if you enable skipDispatchOnTransition, the backend transition will happen as expected, but the new backend may not handle the first event!

In this example, the first touchstart event would trigger the TouchBackend to replace the HTML5Backend—but the user would have to start a new touch event for the TouchBackend to register a drag.

Preview

Concerning the Preview class, it is created using the following snippet:

  import MultiBackend, { Preview } from 'react-dnd-multi-backend';
  ...
  <Preview generator={this.generatePreview} />

You must pass a function as the generator prop which takes 3 arguments:

• type: the type of the item (monitor.getItemType())
• item: the item (monitor.getItem())
• style: an object representing the style (used for positioning), it should be passed to the style property of your preview component

Note that this component will only be showed while using a backend flagged with preview: true (see Create a custom pipeline) which is the case for the Touch backend in the default HTML5toTouch pipeline.

Examples

You can see an example here.

Migrating

Migrating from 2.x.x

In 2.x.x, the pipeline was static but corresponded with the behavior of HTML5toTouch, so just including and passing this pipeline as a parameter would give you the same experience as before.

If you used the start option, it's a bit different. With start: 0 or start: Backend.HTML5, MultiBackend simply used the default pipeline, so you can also just pass HTML5toTouch. With start: 1 or start: Backend.TOUCH, MultiBackend would only use the TouchBackend, so you can replace MultiBackend with TouchBackend (however, you would lose the Preview component) or create a simple pipeline (see Create a custom pipeline) and pass it as a parameter:

var TouchOnly = { backends: [{ backend: TouchBackend, preview: true }] };

Migrating from 3.1.2

Starting with 3.1.8, the dependencies of react-dnd-multi-backend changed. react, react-dom, react-dnd become peer dependencies and you need to install them manually as dependencies in your project package.json.

Note that if you use the HTML5toTouch pipeline, the same is true for react-dnd-html5-backend and react-dnd-touch-backend.

Migrating from 3.x.x

Starting with 4.0.0, react-dnd-multi-backend will start using react-dnd (and the corresponding backends) 9.0.0 and later.

This means you need to transition from DragDropContext(MultiBackend(HTML5toTouch))(App) to <DndProvider backend={MultiBackend} options={HTML5toTouch}>. Accordingly, the pipeline syntax changes and you should specify backend options as a separate property, e.g. {backend: TouchBackend({enableMouseEvents: true})} becomes {backend: TouchBackend, options: {enableMouseEvents: true}}.

License

MIT, Copyright (c) 2016-2019 Louis Brunner