Accordion list

components.accordion-item.js

// components/accordion-item.js

import Ember from 'ember';

export default Ember.Component.extend({
  item: null,
  activeItem: null,
  
  isExpanded: Ember.computed('activeItem', 'item', function() {
    return this.get('activeItem') === this.get('item');
  })
});

components.accordion-list.js

// components/accordion-list.js

import Ember from 'ember';

export default Ember.Component.extend({
  items: null,
  activeItem: null,
  actions: {
    toggleActiveItem(item) {
      if (this.get('activeItem') !== item) {
        this.set('activeItem', item);
      } else {
        this.set('activeItem', null);
      } 
    }
  }
});

controllers.application.js

// controllers/application.js
import Ember from 'ember';

export default Ember.Controller.extend({
  items: Ember.computed(function() {
    return [
      {title: "Item 1", details: "Details here"},
      {title: "Item 2", details: "Details here"},
      {title: "Item 3", details: "Details here"}
    ]
  })
});

initial-diagram.txt

+---------------------------------+
 |           accordion list        |
 +---+------------------+----------+
     ^                  |
     |                  | item, expandedItem
toggleExpanded          |
     |                  |
     |        +---------v----------+
     |        |  accordion-item    |
     +--------+                    |
              +--------------------+

styles.app.css

body {
  margin: 12px 16px;
  font-family: 'Helvetica Neue', Helvetica, Arial, sans-serif;
  font-size: 12pt;
}

.header {
  background: #eee;
  padding: 10px;
}

.details {
  padding: 10px 10px 20px 10px;
}

templates.application.hbs

<!-- application.hbs -->
<h1>Accordion!</h1>
{{accordion-list items=items}}
<br>
<br>

templates.components.accordion-item.hbs

<!-- components/accordion-item.hbs -->

<div class='header' {{action headerClicked}}>{{item.title}} (click to {{if isExpanded 'close' 'open'}})</div>
{{#if isExpanded}}
  <div class='details'>{{item.details}}</div>
{{/if}}

templates.components.accordion-list.hbs

<!-- components/accordion-list.hbs -->

<div>
{{#each items as |item|}}
  {{accordion-item
      item=item
      activeItem=activeItem
      headerClicked=(action 'toggleActiveItem' item)}}
{{/each}}
</div>

twiddle.json

{
  "version": "0.10.4",
  "EmberENV": {
    "FEATURES": {}
  },
  "options": {
    "use_pods": false,
    "enable-testing": false
  },
  "dependencies": {
    "jquery": "https://cdnjs.cloudflare.com/ajax/libs/jquery/1.11.3/jquery.js",
    "ember": "2.7.0",
    "ember-data": "2.7.0",
    "ember-template-compiler": "2.7.0"
  },
  "addons": {}
}