Creating Custom Previews

The Decap CMS exposes a window.CMS global object that you can use to register custom widgets, previews and editor plugins. The available customization methods are:

registerPreviewStyle: Register a custom stylesheet to use on the preview pane.
registerPreviewTemplate: Registers a template for a collection.

React Components inline interaction

Decap CMS is a collection of React components and exposes two constructs globally to allow you to create components inline: ‘createClass’ and ‘h’ (alias for React.createElement).

`registerPreviewStyle`

CMS.registerPreviewStyle(file);

Params:

file: css file path

Example:

// index.html
<script src="https://unpkg.com/decap-cms@^3.0.0/dist/decap-cms.js"></script>
<script>
  CMS.registerPreviewStyle("/example.css");
</script>

/* example.css */

html,
body {
  color: #444;
  font-size: 14px;
  font-family: 'Helvetica Neue', Helvetica, Arial, sans-serif;
}

body {
  padding: 20px;
}

`registerPreviewTemplate`

Registers a template for a folder collection or an individual file in a file collection.

CMS.registerPreviewTemplate(name, react_component);

Params:

name: The name of the collection (or file for file collections) which this preview component will be used for.
- Folder collections: Use the name of the collection
- File collections: Use the name of the file

react_component: A React component that renders the collection data. Six props will be passed to your component during render:

entry: Immutable collection containing the entry data.
widgetFor: Returns the appropriate widget preview component for a given field.
widgetsFor: Returns an array of objects with widgets and associated field data. For use with list and object type entries.

getAsset: Returns the correct filePath or in-memory preview for uploaded images. Example:

<script src="https://unpkg.com/decap-cms@^3.0.0/dist/decap-cms.js"></script>
<script>
  var PostPreview = createClass({
    render: function() {
      var entry = this.props.entry;
      var image = entry.getIn(['data', 'image']);
      var bg = this.props.getAsset(image);
      return h('div', {},
        h('h1', {}, entry.getIn(['data', 'title'])),
        h('img', {src: bg.toString()}),
        h('div', {"className": "text"}, this.props.widgetFor('body'))
      );
    }
  });

  CMS.registerPreviewTemplate("posts", PostPreview);
</script>

document: The preview pane iframe's document instance.
window: The preview pane iframe's window instance.

Lists and Objects

The API for accessing the individual fields of list- and object-type entries is similar to the API for accessing fields in standard entries, but there are a few key differences. Access to these nested fields is facilitated through the widgetsFor function, which is passed to the preview template component during render. Note: as is often the case with the Decap CMS API, arrays and objects are created with Immutable.js. If some of the methods that we use are unfamiliar, such as getIn, check out their docs to get a better understanding. List Example:

<script>
var AuthorsPreview = createClass({
  // For list fields, the widgetFor function returns an array of objects
  // that you can map over in your template. If our field is a list of
  // authors containing two entries, with fields `name` and `description`,
  // the return value of `widgetsFor` would look like this:
  //
  // [{
  //   data: { name: 'Mathias', description: 'Co-Founder'},
  //   widgets: { name: (<WidgetComponent>), description: (WidgetComponent>)}
  // },
  // {
  //   data: { name: 'Chris', description: 'Co-Founder'},
  //   widgets: { name: (<WidgetComponent>), description: (WidgetComponent>)}
  // }]
  //
  // Templating would look something like this:

  render: function() {
    return h('div', {},

      // This is a static header that would only be rendered once for the entire list
      h('h1', {}, 'Authors'),

      // Here we provide a simple mapping function that will be applied to each
      // object in the array of authors
      this.props.widgetsFor('authors').map(function(author, index) {
        return h('div', {key: index},
          h('hr', {}),
          h('strong', {}, author.getIn(['data', 'name'])),
          author.getIn(['widgets', 'description'])
        );
      })
    );
  }
});
CMS.registerPreviewTemplate("authors", AuthorsPreview);
</script>

Object Example:

<script>
var GeneralPreview = createClass({
  // Object fields are simpler than lists - instead of `widgetsFor` returning
  // an array of objects, it returns a single object. Accessing the shape of
  // that object is the same as the shape of objects returned for list fields:
  //
  // {
  //   data: { front_limit: 0, author: 'Chris' },
  //   widgets: { front_limit: (<WidgetComponent>), author: (WidgetComponent>)}
  // }
  render: function() {
    var entry = this.props.entry;
    var title = entry.getIn(['data', 'site_title']);
    var posts = entry.getIn(['data', 'posts']);

    return h('div', {},
      h('h1', {}, title),
      h('dl', {},
        h('dt', {}, 'Posts on Frontpage'),
        h('dd', {}, this.props.widgetsFor('posts').getIn(['widgets', 'front_limit']) || 0),

        h('dt', {}, 'Default Author'),
        h('dd', {}, this.props.widgetsFor('posts').getIn(['data', 'author']) || 'None'),
      )
    );
  }
});

CMS.registerPreviewTemplate("general", GeneralPreview);
</script>

Accessing Metadata

Preview Components also receive an additional prop: fieldsMetaData. It contains additional information (besides the plain textual value of each field) that can be useful for preview purposes. For example, the Relation widget passes the whole selected relation data in fieldsMetaData.

export default class ArticlePreview extends React.Component {
  render() {
    const {entry, fieldsMetaData} = this.props;
    const author = fieldsMetaData.getIn(['authors', data.author]);

    return <article><h2>{ entry.getIn(['data', 'title']) }</h2>
      {author &&<AuthorBio author={author.toJS()}/>}
    </article>
  }
}