SGH / COMPONENTS

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<link rel="import" href="../polymer/polymer.html">
<link rel="import" href="../paper-styles/default-theme.html">
<link rel="import" href="../paper-input/paper-input.html">
<link rel="import" href="../paper-menu-button/paper-menu-button.html">
<link rel="import" href="../paper-ripple/paper-ripple.html">
<link rel="import" href="../iron-a11y-keys-behavior/iron-a11y-keys-behavior.html">
<link rel="import" href="../iron-behaviors/iron-control-state.html">
<link rel="import" href="../iron-behaviors/iron-button-state.html">
<link rel="import" href="../iron-icons/iron-icons.html">
<link rel="import" href="../iron-icon/iron-icon.html">
<link rel="import" href="../iron-selector/iron-selectable.html">

<!--
`paper-dropdown-menu` is similar to a native browser select element.
`paper-dropdown-menu` works with selectable content. The currently selected
item is displayed in the control. If no item is selected, the `label` is
displayed instead.

The child element with the class `dropdown-content` will be used as the dropdown
menu. It could be a `paper-menu` or element that triggers `iron-select` when
selecting its children.

Example:

    <paper-dropdown-menu label="Your favourite pastry">
      <paper-menu class="dropdown-content">
        <paper-item>Croissant</paper-item>
        <paper-item>Donut</paper-item>
        <paper-item>Financier</paper-item>
        <paper-item>Madeleine</paper-item>
      </paper-menu>
    </paper-dropdown-menu>

This example renders a dropdown menu with 4 options.

### Styling

The following custom properties and mixins are also available for styling:

Custom property | Description | Default
----------------|-------------|----------
`--paper-dropdown-menu` | A mixin that is applied to the element host | `{}`
`--paper-dropdown-menu-disabled` | A mixin that is applied to the element host when disabled | `{}`
`--paper-dropdown-menu-ripple` | A mixin that is applied to the internal ripple | `{}`
`--paper-dropdown-menu-button` | A mixin that is applied to the internal menu button | `{}`
`--paper-dropdown-menu-input` | A mixin that is applied to the internal paper input | `{}`
`--paper-dropdown-menu-icon` | A mixin that is applied to the internal icon | `{}`

You can also use any of the `paper-input-container` and `paper-menu-button`
style mixins and custom properties to style the internal input and menu button
respectively.

@group Paper Elements
@element paper-dropdown-menu
@hero hero.svg
@demo demo/index.html
-->

<dom-module id="paper-dropdown-menu">
  <style>
    :host {
      display: inline-block;
      position: relative;
      text-align: left;
      cursor: pointer;

      --paper-input-container-input: {
        overflow: hidden;
        white-space: nowrap;
        text-overflow: ellipsis;
        max-width: 100%;
        box-sizing: border-box;
        cursor: pointer;
      };

      @apply(--paper-dropdown-menu);
    }

    :host([disabled]) {
      @apply(--paper-dropdown-menu-disabled);
    }

    :host([noink]) paper-ripple {
      display: none;
    }

    :host([no-label-float]) paper-ripple {
      top: 8px;
    }

    paper-ripple {
      top: 20px;
      left: 8px;
      bottom: 16px;
      right: 8px;

      @apply(--paper-dropdown-menu-ripple);
    }

    paper-menu-button {
      @apply(--paper-dropdown-menu-button);
    }

    paper-input {
      @apply(--paper-dropdown-menu-input);
    }

    iron-icon {
      color: var(--disabled-text-color);

      @apply(--paper-dropdown-menu-icon);
    }

  </style>
  <template>
    <paper-menu-button
      id="menuButton"
      vertical-align="top"
      horizontal-align="right"
      vertical-offset="[[_computeMenuVerticalOffset(noLabelFloat)]]"
      disabled="[[disabled]]"
      no-animations="[[noAnimations]]"
      on-iron-select="_onIronSelect"
      opened="{{opened}}">
      <div class="dropdown-trigger">
        <paper-ripple></paper-ripple>
        <paper-input
          readonly
          disabled="[[disabled]]"
          value="[[selectedItemLabel]]"
          placeholder="[[placeholder]]"
          always-float-label="[[alwaysFloatLabel]]"
          no-label-float="[[noLabelFloat]]"
          label="[[label]]">
          <iron-icon icon="arrow-drop-down" suffix></iron-icon>
        </paper-input>
      </div>
      <content id="content" select=".dropdown-content"></content>
    </paper-menu-button>
  </template>
</dom-module>
<script>
  (function() {
    'use strict';

    Polymer({
      is: 'paper-dropdown-menu',

      /**
       * Fired when the dropdown opens.
       *
       * @event paper-dropdown-open
       */

      /**
       * Fired when the dropdown closes.
       *
       * @event paper-dropdown-close
       */

      behaviors: [
        Polymer.IronControlState,
        Polymer.IronButtonState
      ],

      properties: {
        /**
         * The derived "label" of the currently selected item. This value
         * is the `label` property on the selected item if set, or else the
         * trimmed text content of the selected item.
         */
        selectedItemLabel: {
          type: String,
          notify: true,
          computed: '_computeSelectedItemLabel(selectedItem)'
        },

        /**
         * The last selected item. An item is selected if the dropdown menu has
         * a child with class `dropdown-content`, and that child triggers an
         * `iron-select` event with the selected `item` in the `detail`.
         */
        selectedItem: {
          type: Object,
          notify: true,
          readOnly: true
        },

        /**
         * The label for the dropdown.
         */
        label: {
          type: String
        },

        /**
         * The placeholder for the dropdown.
         */
        placeholder: {
          type: String
        },

        /**
         * True if the dropdown is open. Otherwise, false.
         */
        opened: {
          type: Boolean,
          notify: true,
          value: false
        },

        /**
         * Set to true to disable the floating label. Bind this to the
         * `<paper-input-container>`'s `noLabelFloat` property.
         */
        noLabelFloat: {
            type: Boolean,
            value: false,
            reflectToAttribute: true
        },

        /**
         * Set to true to always float the label. Bind this to the
         * `<paper-input-container>`'s `alwaysFloatLabel` property.
         */
        alwaysFloatLabel: {
          type: Boolean,
          value: false
        },

        /**
         * Set to true to disable animations when opening and closing the
         * dropdown.
         */
        noAnimations: {
          type: Boolean,
          value: false
        }
      },

      listeners: {
        'tap': '_onTap'
      },

      keyBindings: {
        'up down': 'open',
        'esc': 'close'
      },

      hostAttributes: {
        role: 'group',
        'aria-haspopup': 'true'
      },

      attached: function() {
        // NOTE(cdata): Due to timing, a preselected value in a `IronSelectable`
        // child will cause an `iron-select` event to fire while the element is
        // still in a `DocumentFragment`. This has the effect of causing
        // handlers not to fire. So, we double check this value on attached:
        var contentElement = this.contentElement;
        if (contentElement && contentElement.selectedItem) {
          this._setSelectedItem(contentElement.selectedItem);
        }
      },

      /**
       * The content element that is contained by the dropdown menu, if any.
       */
      get contentElement() {
        return Polymer.dom(this.$.content).getDistributedNodes()[0];
      },

      /**
       * Show the dropdown content.
       */
      open: function() {
        this.$.menuButton.open();
      },

      /**
       * Hide the dropdown content.
       */
      close: function() {
        this.$.menuButton.close();
      },

      /**
       * A handler that is called when `iron-select` is fired.
       *
       * @param {CustomEvent} event An `iron-select` event.
       */
      _onIronSelect: function(event) {
        this._setSelectedItem(event.detail.item);
      },

      /**
       * A handler that is called when the dropdown is tapped.
       *
       * @param {CustomEvent} event A tap event.
       */
      _onTap: function(event) {
        if (Polymer.Gestures.findOriginalTarget(event) === this) {
          this.open();
        }
      },

      /**
       * Compute the label for the dropdown given a selected item.
       *
       * @param {Element} selectedItem A selected Element item, with an
       * optional `label` property.
       */
      _computeSelectedItemLabel: function(selectedItem) {
        if (!selectedItem) {
          return '';
        }

        return selectedItem.label || selectedItem.textContent.trim();
      },

      /**
       * Compute the vertical offset of the menu based on the value of
       * `noLabelFloat`.
       *
       * @param {boolean} noLabelFloat True if the label should not float
       * above the input, otherwise false.
       */
      _computeMenuVerticalOffset: function(noLabelFloat) {
        // NOTE(cdata): These numbers are somewhat magical because they are
        // derived from the metrics of elements internal to `paper-input`'s
        // template. The metrics will change depending on whether or not the
        // input has a floating label.
        return noLabelFloat ? -4 : 16;
      }
    });
  })();
</script>