px-dropdown.html

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Copyright (c) 2018, General Electric

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
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    http://www.apache.org/licenses/LICENSE-2.0

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WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
-->

<link rel="import" href="../polymer/polymer.html"/>
<link rel="import" href="css/px-dropdown-styles.html"/>

<link rel="import" href="px-dropdown-trigger.html"/>
<link rel="import" href="px-dropdown-content.html"/>
<link rel="import" href="../px-overlay/px-overlay-content.html"/>
<link rel="import" href="../px-overlay/px-overlay-behavior.html"/>
<link rel="import" href="../iron-resizable-behavior/iron-resizable-behavior.html"/>
<link rel="import" href="../iron-media-query/iron-media-query.html"/>

<!--
A dropdown from which users can select one or more values. Acts like a native
browser "select" element with more fine-tuned interaction behaviors and a
configurable UI.

Dropdown can be used in conjunction with px-validation to apply validation states.
Add the `validation-error`, `validation-warning`, or `validation-success` classes
to alter the border color of the component.

### Usage

#### Simple

```
<px-dropdown items='["One","Two"]'></px-dropdown>
<px-dropdown items='[{"key":"one", "val": "One"}, {"key":"two", "val": "Two"}]'></px-dropdown>
```

#### Complex

```
<px-dropdown
    items='[{"key":"one", "val": "One", "selected": "true"}]'
    display-value="Click me"
    prevent-close-on-outside-click="true"
    allow-outside-scroll="true"
    multi="true"
    select-by="key"
    selected-values='["1","3"]'
    bound-target=".parentDiv"
    search-mode="true"
    sort-mode="val">
</px-dropdown>
```

#### Custom trigger

By default, the `displayValue` or `icon` properties can be used to customize
the information shown in the dropdown trigger button. Additional properties
are available to further customize the trigger. To create a custom trigger which
does not match any of the available configurations, pass an element into the
`trigger` slot. This element can be anything — a button, a div, some text, etc. The
dropdown will attach a tap event listener to the element to listen for user
interactions which should open the dropdown. You should also give the element a
`tabindex=0` and `id=trigger` to maintain keyboard accessibility.

```
<px-dropdown items='[{"key":"one", "val": "One", "selected": "true"}]'>
  <button slot="trigger" id="trigger" tabindex="0">Unstyled dropdown trigger</button>
</px-dropdown>
```

### Styling

The following custom properties are available for styling of the dropdown content.
See the documentation for px-buttons-design for variables related to the styling of the invoking button.

Custom property | Description
:----------------|:-------------
`--px-dropdown-min-height` | Min height for the dropdown menu container
`--px-dropdown-min-width` | Min width for the dropdown menu container
`--px-dropdown-max-height` | Max height for the dropdown menu container
`--px-dropdown-max-width` | Max width for the dropdown menu container
`--px-dropdown-border-color` | Border color for the dropdown menu container
`--px-dropdown-bg-color` | Background color for the dropdown menu container
`--px-dropdown-bg-color--hover` | Background color of a hovered menu item
`--px-dropdown-bg-color--selected` | Background color of a selected menu item
`--px-dropdown-text-color` | Text color of a regular dropdown menu item
`--px-dropdown-text-color--disabled` | Text color of a disabled dropdown menu item
`--px-dropdown-text-color--selected` | Text color of a selected dropdown menu item
`--px-dropdown-icon-size` | Size for the icon in the dropdown trigger
`--px-dropdown-font-weight` | Font weight for the dropdown trigger button
`--px-dropdown-item-icon-size` | Size of the optional icon in each dropdown item
`--px-dropdown-item-padding` | Padding of each dropdown item
`--px-dropdown-item-height` | Height of each dropdown item
`--px-dropdown-content-font-size` | Font size in the dropdown menu container
`--px-dropdown-caret-left` | Horizontal offset of the caret when dropdown aligned left
`--px-dropdown-caret-right` | Horizontal offset of the caret when dropdown aligned right

@element px-dropdown
@blurb Element providing a dropdown solution.
@homepage index.html
@demo index.html
-->
<dom-module id="px-dropdown">
  <template>
    <style include="px-dropdown-styles"></style>
    <iron-media-query query$="(max-width: {{mobileAt}}px)" query-matches="{{mobile}}"></iron-media-query>
    <div id="target">
      <slot name="trigger" id="triggerSlot">
        <px-dropdown-trigger
          id="trigger"
          opened="[[opened]]"
          language="[[language]]"
          resources="[[resources]]"
          use-key-if-missing="[[useKeyIfMissing]]"
          disabled="[[disabled]]"
          hide-chevron="[[hideChevron]]"
          display-value="[[displayValue]]"
          disable-clear="[[disableClear]]"
          selected="[[selected]]"
          selected-values="[[selectedValues]]"
          button-style="[[buttonStyle]]"
          icon="[[icon]]"
          display-value-selected="[[_displayValueSelected]]">
        </px-dropdown-trigger>
      </slot>
    </div>
    <px-overlay-content
      hoist="[[hoist]]"
      container-type="[[containerType]]"
      event-names='["px-dropdown-click","px-dropdown-selection-changed"]'>
      <px-dropdown-content
        id="content"
        items="[[items]]"
        multi="[[multi]]"
        opened="{{opened}}"
        key-bindings-target="[[_keyBindingsTarget]]"
        display-value="[[displayValue]]"
        language="[[language]]"
        resources="[[resources]]"
        use-key-if-missing="[[useKeyIfMissing]]"
        disabled="[[disabled]]"
        bound-target="[[boundTarget]]"
        prevent-close-on-outside-click="[[preventCloseOnOutsideClick]]"
        disable-select="[[disableSelect]]"
        select-by="[[selectBy]]"
        selected="{{selected}}"
        selected-values="{{selectedValues}}"
        selected-items="{{selectedItems}}"
        trigger-height="[[triggerHeight]]"
        show-caret="[[showCaret]]"
        disable-dynamic-align="[[disableDynamicAlign]]"
        vertical-align="[[verticalAlign]]"
        horizontal-align="[[horizontalAlign]]"
        mobile="{{mobile}}"
        mobile-at="[[mobileAt]]"
        hide-mobile-buttons="[[hideMobileButtons]]"
        search-mode="[[searchMode]]"
        search-term="[[searchTerm]]"
        sort-mode="[[sortMode]]"
        hide-selected="[[hideSelected]]"
        allow-outside-scroll="[[allowOutsideScroll]]"
        display-value-selected="{{_displayValueSelected}}"
        disable-truncate="[[disableTruncate]]">
      </px-dropdown-content>
    </px-overlay-content>
  </template>
</dom-module>
<script>
  Polymer({
    is: 'px-dropdown',
    behaviors: [
      PxOverlayBehavior.sharedProperties,
      Polymer.IronResizableBehavior
    ],
    listeners: {
      'iron-resize' : '_resetMinWidth'
    },
    properties: {
      /**
       * A flag which reflects if the dropdown trigger has been clicked or not.
       */
      opened: {
        type: Boolean,
        notify: true,
        value: false
      },
      /**
       * Whether or not to hide the chevron icon from the dropdown.
       */
      hideChevron: {
        type: Boolean,
        value: false
      },
      /**
       * A CSS selector which specifies the bounding target the dropdown will be
       * displayed within. Defaults to `window`.
       */
      boundTarget: {
        type: String
      },
      /**
       * Whether the dropdown will close when a user clicks
       * outside of it. Set to true to prevent dropdown from closing.
       */
      preventCloseOnOutsideClick: {
        type: Boolean,
        value: false
      },
      /**
       * The placeholder text to display in the dropdown. If the
       * selected value(s) are cleared out, the displayValue will be
       * replaced in the dropdown.
       */
      displayValue: {
        type: String,
        notify: true,
        value: 'Select',
        observer: '_resetMinWidth'
      },
      /**
       * If set to true, users are unable to clear out the dropdown
       * once a selection has been made. Useful for required single-select
       * dropdowns where an empty state would be undesirable. Not recommended
       * for multi-select dropdowns, as it means the user will simply lose the ability
       * to quickly deselect all checked options (there is currently no mechanism
       * which requires a user to select at least one option).
       */
      disableClear: {
        type: Boolean,
        value: false
      },
      /**
       * If set to true, users can still open the dropdown and click on items,
       * but they will not be selected. Use this property in use cases where
       * the dropdown is used as a menu instead of a form input.
       */
      disableSelect: {
        type: Boolean,
        value: false
      },
      /**
       * By default, dropdown items longer than the max-width of the dropdown
       * will be truncated, with the full string available on hover tooltip.
       * If this property is set, items will not be truncated, but will wrap instead.
       */
      disableTruncate: {
        type: Boolean,
        value: false
      },
      /**
       * The text that is displayed in the label of the dropdown.
       * Updated when the selections change.
       */
       _displayValueSelected: {
        type: String
      },
      /**
       * An array that contains the list of items which show up in the dropdown.
       * Each item can either be a simple string, or an object consisting of:
       * * 'key' - a unique identifier (number or string)
       * * 'val' - the actual text that is displayed
       * * 'disabled' - whether the item should be disabled completely - can't be selected nor used as a menu option (optional)
       * * 'disableSelect` - whether the item should be disabled for selection, but can still be used as a menu option (optional)
       * * 'selected' - whether the item should be selected at instantiation (optional)
       * * 'icon' - an icon name from the px-icon-set to display next to the item (optional)
       * * 'color' - the color to use for the icon - if not specified, the default text colors will be used (optional)
       *
       * Note: if you specify more than one item as `selected`, but `multi` is not enabled,
       * only the *first* selected item will be chosen. See also `clearSelectionsOnChange`.
       */
      items: {
        type: Array,
        notify: true,
        value: function () {
          return [];
        }
      },
      /**
       * If set to true, multiple values can be selected in the dropdown.
       * Selected values are reflected in the `selectedValues` property.
       * If set to false, a single selected value is reflected in `selected`.
       */
      multi: {
        type: Boolean,
        value: false
      },
      /**
       * Which property of each dropdown item will be used to get/set
       * the selected items - should be one of "key" or "val".
       */
      selectBy: {
        type: String,
        value: 'key'
      },
      /**
       * Gets or sets the selected item when `multi` is false.
       * Will either be a single key or value based on `selectBy`.
       */
      selected: {
        type: String,
        value: null,
        notify: true
      },
      /**
       * Gets or sets the selected items when `multi` is true.
       * Will either be an array of keys or values based on `selectBy`.
       */
      selectedValues: {
        type: Array,
        notify: true
      },
      /**
       * A read-only array of the selected `<div>` elements in the dropdown.
       */
      selectedItems: {
        type: Array,
        value: function() {
          return [];
        },
        readOnly: true
      },
      /**
       * By default, the dropdown will constrain scrolling on the page to
       * itself when opened. Set to true in order to allow scrolling of
       * the page while the dropdown is open.
       */
      allowOutsideScroll: {
        type: Boolean,
        value: false
      },
      /**
       * Style for the button that invokes the dropdown.
       * One of 'default','bare','bare--primary', 'tertiary', or 'icon'.
       */
      buttonStyle: {
        type: String,
        value: 'default'
      },
      /**
       * Whether the dropdown should be disabled and non-interactive.
       */
      disabled: {
        type: Boolean,
        value: false
      },
      /**
       * If true, the dropdown will include a search box, whereby the
       * dropdown items can be filtered with a search term.
       */
      searchMode: {
        type: Boolean,
        value: false
      },
      /**
       * The value of the search box, used for filtering the dropdown
       * items when searchMode is true.
       */
      searchTerm: {
        type: String,
        value: ''
      },
      /**
       * What to sort the dropdown items by - one of "key" or "val".
       * By default, the items will be displayed in the order they are
       * passed into the component.
       */
      sortMode: {
        type: String
      },
      /**
       * If set to true, the display-value will always show up in the
       * invoking button of the dropdown. Useful in cases like the
       * px-data-table, where "Show/Hide Columns" should always appear.
       */
      hideSelected: {
        type: Boolean,
        value: false
      },
      /**
       * If buttonStyle is set to 'icon' this property will dictate
       * which icon will be displayed inside of the dropdown button.
       * The `displayValue`, selected values, and chevron will not be displayed.
       * Perfect for icon-invoked menus. The value of this property should
       * be a valid px-icon name, e.g. 'px-utl:app-settings'
       */
      icon: {
        type: String,
        value: ''
      },
      /**
      * Set this property if you would like the `selected` and `selectedValues`
      * properties to be cleared whenever mutations are made to the `items` array.
      */
      clearSelectionsOnChange: {
        type: Boolean,
        value: false
      },
      /**
       * The height of the trigger element, used for calculating offset distance
       * for the dropdown. Set this value if you use the `trigger` slot.
       */
      triggerHeight: {
        type: Number,
        value: 30
      },
      /**
       * By default, the dropdown menu will be flush against the trigger.
       * Enable this property to show a caret between the two. Useful
       * in iconic menus and used by the application/product switcher.
       */
      showCaret: {
        type: Boolean,
        value: false
      },
      /**
       * By default the dropdown will attempt to automatically align itself
       * vertically and horizontally based on the available space. Set this flag
       * to turn off that automatic behavior and force a certain `verticalAlign` / `horizontalAlign`.
       */
      disableDynamicAlign: {
        type: Boolean,
        value: false
      },
      /**
       * Vertical alignment of the dropdown relative to the trigger.
       * Should be one of `top` or `bottom` where `top` means that the dropdown
       * and trigger are aligned at the top, so the dropdown will extend _below_ the trigger.
       * Overridden by dynamic alignment, unless `disableDynamicAlign` is true.
       */
      verticalAlign: {
        type: String,
        value: 'top'
      },
      /**
       * Horizontal alignment of the dropdown relative to the trigger.
       * Should be one of `left` or `right` where `left` means that the dropdown
       * and trigger are aligned on their left side, so the dropdown will extend _to the right_.
       * Overridden by dynamic alignment, unless `disableDynamicAlign` is true.
       */
      horizontalAlign: {
        type: String,
        value: 'left'
      },
      /**
       * Whether to display the mobile version of the dropdown, which appears as a fullscreen modal.
       * Automatically detected based on the breakpoint specified in `mobileAt`.
       */
      mobile: {
        type: Boolean,
        reflectToAttribute: true
      },
      /**
       * The breakpoint (in # of pixels) at which to display the mobile version of px-dropdown.
       */
      mobileAt: {
        type: Number,
        value: 400
      },
      /**
       * By default, the mobile dropdown will show Apply/Clear buttons.
       * Set this property to hide them.
       */
      hideMobileButtons: {
        type: Boolean,
        value: false
      },
      /**
       * A valid IETF language tag as a string that `app-localize-behavior` will
       * use to localize this component.
       *
       * See https://github.com/PolymerElements/app-localize-behavior for API
       * documentation and more information.
       */
      language: {
        type: String,
        value: 'en'
      },
      useKeyIfMissing: {
        type: Boolean,
        value: true
      },
      /**
       * A dictionary of strings used within the component for AppLocalizeBehavior
       * to use, based on the selected `language` property.
       */
      resources: {
        type: Object,
        value: function() {
          return {
            'en': {
              "selected": "selected",
              "Clear": "Clear",
              "Apply": "Apply"
            }
          }
        }
      },
      /**
       * Binding target for iron-a11y-keys
       */
      _keyBindingsTarget: {
        type: HTMLElement,
        value: function () {
          return this;
        }
      },
      /**
       * The currently "focused" option in the dropdown list.
       * Used for handling of keyboard events.
       */
      _focusedOption: {
        type: HTMLElement
      },
      /**
       * Used to capture if the user is using the keyboard to interact with the dropdown.
       * Used to disable all mouse events.
       */
      _keyboardBeingUsed: {
        type: Boolean,
        value: false
      },
      /**
       * Specifies if the dropdown content should get hoisted to a container in order to escape its current stacking context
       */
      hoist: {
        type: Boolean,
        value: false
      }
    },
    created: function() {
      /**
       * Finds the trigger element and assigns it to the `openTrigger` property.
       * Called when the element is first attached and whenever the `slotchange`
       * event is fired.
       */
      this._initOpenTrigger = function() {
        var trigger = this._getSlottedOpenTrigger();
        if (trigger) {
          this.$.content.openTrigger = trigger;
        }
      }.bind(this);
    },
    attached: function() {
      this.$.triggerSlot.addEventListener('slotchange', this._initOpenTrigger, false);
      this._initOpenTrigger();

      Polymer.RenderStatus.afterNextRender(this, function() {
        // Forces the width of the dropdown to be at least as wide as the trigger
        this.$.content.style.minWidth = window.getComputedStyle(this.$.trigger).width;
      }.bind(this));
    },
    detached: function() {
      this.$.triggerSlot.removeEventListener('slotchange', this._initOpenTrigger);
    },
    _resetMinWidth: function() {
      this.$.content.style.minWidth = window.getComputedStyle(this.$.trigger).width;
    },
    /**
     * Toggles visibility of the dropdown: opens dropdown if it is closed, and
     * closes dropdown if it is open.
     */
    toggle: function() {
      this.$.content.toggle();
      Polymer.RenderStatus.afterNextRender(this, function() {
        this.$.content.style.minWidth = window.getComputedStyle(this.$.trigger).width;
      }.bind(this));
    },
    /**
     * Finds the element in the the trigger slot. If the developer passed an
     * element into the `slot="trigger"` slot, returns that element. Otherwise
     * returns the default trigger in the Shadow DOM. Works for Polymer 1.x and
     * Polymer 2.x, which have different APIs for accomplishing this.
     *
     * @return {HTMLElement|null} - Reference to the trigger element, or null if none found
     */
    _getSlottedOpenTrigger: function() {
      var elems;
      if (Polymer.Element) {
        var nodes = Polymer.FlattenedNodesObserver.getFlattenedNodes(this.$.triggerSlot);
        elems = nodes.filter(function(n) {
          return n.nodeType === Node.ELEMENT_NODE;
        });
      } else {
        elems = this.getContentChildren('#triggerSlot');
      }
      if (elems.length > 1) {
        console.warn('Only expected 1 element as a child of the "trigger" slot.')
      }
      var [trigger] = elems;
      return (trigger instanceof HTMLElement) ? trigger : null;
    },
    /**
     * Resizes the dropdown when the search term is changed.
     */
    _notifyResize: function() {
      // Debounce to try to stop notify resize from spamming with events, which
      // slows things down in Polymer 2.x + IE
      this.debounce('on-notify-resize', function() {
        this.$.content._notifyResize();
      }, 1);
    }

    /**
    * @event px-dropdown-selection-changed
    *
    * Event fired when any given element is selected or deselected in the dropdown.
    * `evt.detail` contains:
    * ```
    * { val: "text of the changed element",
    *   key: "key of the changed element",
    *   selected: true/false }
    * ```
    */
  });
</script>