Ember Collection

An efficient incremental rendering component with support for custom layouts and large lists.

Table of Contents

1. Installation
2. Usage
3. Layouts
4. Build it
5. How it works
6. Run unit tests

Installation

• ember install ember-collection

Submitting bugs

TODO - Create a base ember twiddle with EmberCollection setup.

It would help us greatly to help you and to improve ember collection.

Usage

The height of the collection is inferred from its nearest relative parent. This is so you can just use CSS to style the container.

So, first make sure the collection has a parent with position: relative, and then render a template:

{{#ember-collection
  items=model
  cell-layout=(fixed-grid-layout 800 50) as |item index|
}}
  {{item.name}}
{{/ember-collection}}

Next, let's feed our template with some data:

// define index route and return some data from model
export default Ember.Route.extend({
  model: function() {
    var items = [];
    for (var i = 0; i < 10000; i++) {
      items.push({name: "Item " + i});
    }
    return items;
  }
});

Shazam! You should be able to see a scrollable area with 10,000 items in it.

Required parameters

You must specify cell-layout parameter so that EmberCollection can layout out your items. The provided layouts are described in the Layouts section.

Estimating width/height

You can pass estimated-width and estimated-height to the collection, for situations where the collection cannot infer its height from its parent (e.g., when there's no DOM in FastBoot).

Once the collection has been rendered, estimated-width and estimated-height have no effect.

Actions

scroll-change

If you do not provide a scroll-change action name or closure action, scrolling will work normally.

If you do specify scroll-change, ember-collection assumes that you want to handle the scroll-change action in a true data down, actions up manner. For this reason, ember-collection will not set scroll-left and scroll-top itself, but rather rely on you to update those properties based on action handling as you see fit.

An example of specifying an action and keeping scrolling working normally looks like this:

{{#ember-collection items=model cell-layout=(fixed-grid-layout itemWidth itemHeight)
    scroll-left=scrollLeft scroll-top=scrollTop scroll-change=(action "scrollChange")
    as |item index| }}
  <div class="list-item">{{item.name}}</div>
{{/ember-collection}}

export default Ember.Controller.extend({
  scrollLeft: 0,
  scrollTop: 0,
  actions: {
    scrollChange(scrollLeft, scrollTop) {
      this.set('scrollLeft', scrollLeft);
      this.set('scrollTop', scrollTop);
    }
  }
});

Layouts

Fixed Grid Layout

The fixed-grid-layout will arrange the items in a grid to to fill the content area. The arguments for the layout are:

Argument	Description
itemWidth	The width of each item
itemHeight	The height of each item

{{#ember-collection items=model cell-layout=(fixed-grid-layout itemWidth itemHeight)
    scroll-left=scrollLeft scroll-top=scrollTop scroll-change=(action "scrollChange")
    as |item index| }}
  <div class="list-item">{{item.name}}</div>
{{/ember-collection}}

Mixed Grid Layout

The mixed-grid-layout is used when each item has a known width and height and will arrange the items in rows from left to right fitting as many items in each row as possible. The arguments for the layout are:

Argument	Description
itemSizes	A collection of objects having width and height properties. Used to lookup with size of the corresponding index in the collection.

For example if you want the first element in items to have a size of 20x50 then the first element in itemSizes must be {width: 20, height: 50}. If the items have width and height properties you can use pass collection to items and itemSizes.

{{#ember-collection items=model cell-layout=(mixed-grid-layout itemSizes)
    scroll-left=scrollLeft scroll-top=scrollTop scroll-change=(action "scrollChange")
    as |item index| }}
  <div class="list-item">{{item.name}}</div>
{{/ember-collection}}

Percentage Columns Layout

The percentage-columns-layout allows items to be laid out in a fixed number of columns sized using percentage widths with a fixed height in pixels. The arguments for the layout are:

Argument	Description
itemCount	The number of items passed to the collection. This is usually the number of items in the model (model.length).
columns	An array of numbers not totaling more than 100. e.g. [33.333, 66.666], [25, 50, 10, 15]
itemHeight	The height in pixels of each item.

{{#ember-collection items=model cell-layout=(percentage-columns-layout itemCount columns itemHeight)
    scroll-left=scrollLeft scroll-top=scrollTop scroll-change=(action "scrollChange")
    as |item index| }}
  <div class="list-item">{{item.name}}</div>
{{/ember-collection}}

Creating your own layout

If none of the built in layouts included with EmberCollection fit your needs you can create your own. A layout is simply an object returned from a helper that conforms to the following interface.

import Ember from 'ember'

export default Ember.Helper.helper(function(params, hash) {
   return {
    /**
     * Return an object that describes the size of the content area
     */
    contentSize(clientWidth, clientHeight) {
        return { width, height };
    }
    
    /**
     * Return the index of the first item shown.
     */
    indexAt(offsetX, offsetY, clientWidth, clientHeight) {
        return Number;
    }
    
    /**
     *  Return the number of items to display
     */
    count(offsetX, offsetY, width, height) {
        return Number;
    }
    
    /**
     * Return the css that should be used to set the size and position of the item.
     */
    formatItemStyle(itemIndex, clientWidth, clientHeight) {
        return String;
    }
  } 
});

Build It

1. git clone https://github.com/emberjs/ember-collection.git
2. cd ember-collection
3. npm install (implicitly runs bower install as a postinstall)
4. ember build

How it works

EmberCollection will create enough rows to fill the visible area. It reacts to scroll events and reuses/repositions the rows as scrolled.

Running unit tests

npm install
npm test

Thanks

A lot of the work was sponsored by Yapp Labs, and some work was sponsored by Tightrope Media Systems.