Explorer

Combines a list with an area focusing on a single selected item

Overview

Explorer serves as a base class for implementing item selection user interface patterns that couple two synchronized elements that both support selection. The main "stage" element focuses the user's attention on a single item drawn from a list. A secondary "proxy list" element presents a set of smaller proxy elements, one for each item in the main list. The Explorer keeps the stage and proxy list elements in sync: if the user changes the selection in one element, the selection in the other element is updated to match.

Explorer serves as the basis for a variety of common user interface elements:

Mountain lake Terraced farm Winter trees Forest river Red panda
Demo: Carousel uses a set of dots as proxies, and a SlidingStage as its stage
Page one
Page two
Page three
Demo: Tabs uses TabButton elements as proxies and Modes as its stage
home
Home
search
Search
settings
Settings
Home page
Search page
Settings page
Demo: A Tabs variation for navigation using SlidingStage as the stage
Autumn foliage on mountainside Coastal mountains Dirt road lined with fallen leaves Forest river Hoodoo formations Iceberg Lake with milky water Mountain lake Palm trees Red panda River at sunrise River canyon Sandy beach Snowy peaks Snowy river Stone arch Sunset over rocky ocean pool Sunset through palm trees Terraced farm Winter trees
Demo: ListExplorer uses a ListBox for the proxy list and Modes for the stage

These components present different user interfaces, but they all possess a list synchronized with a stage. The specific form of the stage or proxy list may vary while remaining true to the pattern.

Customizing Explorer using element roles

You can customize Explorer or its subclasses by specifying which tags should be used to fill various element roles:

  • stage: The element used for the main stage. Modes, SlidingStage, CrossfadeStage can all serve as a stage showing a single item at a time. They show different transition effects: an immediate transition, a horizontal sliding effect, and a crossfade effect, respectively.
  • proxy: The element used to instantiate default proxy elements if none are supplied. PlainCarousel uses PlainPageDot as a proxy tag, CarouselWithThumbnails uses img elements as proxies.
  • proxyList: The element used for the list of proxies. The various CenteredStrip components can be used as the proxy list, as can ListBox.

You can create your own components to fill any of these roles. Generally speaking, any component that supports SingleSelectAPIMixin should suffice as the stage or proxy list.

Supplying items to an Explorer

Elements you place inside an Explorer become the list items navigated by the stage element. E.g., you could create the first Carousel demo above like this:

<elix-carousel>
  <img src="image1.jpg" />
  <img src="image2.jpg" />
  <img src="image3.jpg" />
  <img src="image4.jpg" />
  <img src="image5.jpg" />
</elix-carousel>

For each item in the main list, Explorer will create an instance of the element specified by proxyTag. E.g., the PlainCarousel above will instantiate a PlainPageDot for each item (image).

Certain subclasses of Explorer will automatically set the content of the proxy element to reflect data in the corresponding list item. E.g., Tabs will use the aria-label or alt attribute of the list item.

If you want to programmatically manipulate the appearance or content of a proxy element, you can override the Explorer's proxyUpdates method.

Supplying proxies for the items

You can also create proxy elements yourself and slot them into the proxy slot:

<elix-carousel>
  <div slot="proxy">1</div>
  <div slot="proxy">2</div>
  <div slot="proxy">3</div>
  <div slot="proxy">4</div>
  <div slot="proxy">5</div>
  <img src="image1.jpg" />
  <img src="image2.jpg" />
  <img src="image3.jpg" />
  <img src="image4.jpg" />
  <img src="image5.jpg" />
</elix-carousel>
1
2
3
4
5
Mountain lake Terraced farm Winter trees Forest river Red panda
Demo: Carousel with custom proxies

Layout

Explorer manages the top/left/bottom/right visual positioning of the list in relation the stage. You can specify a position through the proxyListPosition property, and control whether the proxy list overlaps the stage with the proxyListOverlap property.

See also

API

Class hierarchy:

The element defines the following shadow parts:

  • proxy: an element representing an item in the list, default type is div element
  • proxy-list: the container for the list of proxies, default type is ListBox
  • stage: the main element showing a single item from the list, default type is Modes

booleanAttributeValue(name, value) static method

Given a string value for a named boolean attribute, return true if the value is either: a) the empty string, or b) a case-insensitive match for the name.

This is native HTML behavior; see the MDN documentation on boolean attributes for the reasoning.

Given a null value, this return false. Given a boolean value, this return the value as is.

Parameters:

  • name: string
  • value: string|boolean|null

Defined by AttributeMarshallingMixin

canGoNext property

True if the item cursor can be moved to the next item, false if not (the current item is the last item in the list).

Type: boolean

canGoPrevious property

True if the item cursor can be moved to the previous item, false if not (the current item is the first one in the list).

Type: boolean

closestAvailableItemIndex(state, options) method

Look for an item which is available in the given state..

The options parameter can accept options for:

  • direction: 1 to move forward, -1 to move backward
  • index: the index to start at, defaults to state.currentIndex
  • wrap: whether to wrap around the ends of the items array, defaults to state.cursorOperationsWrap.

If an available item was found, this returns its index. If no item was found, this returns -1.

Parameters:

  • state: PlainObject
  • options: PlainObject

Returns: number

Defined by ItemsCursorMixin

contentSlot property

See contentSlot.

Defined by SlotContentMixin

currentIndex property

The index of the current item, or -1 if no item is current.

Type: number

Defined by CursorAPIMixin

currentindexchange event

Raised when the currentIndex property changes.

Defined by CursorAPIMixin

currentItem property

The current item, or null if no item is current.

Type: Element

Defined by CursorAPIMixin

currentItemRequired property

True if the list should always have a current item (if it has items).

Type: boolean

Default: false

Defined by CursorAPIMixin

cursorOperationsWrap property

True if cursor operations wrap from last to first, and vice versa.

Type: boolean

Default: false

Defined by CursorAPIMixin

defaultState property

The default state for the component. This can be extended by mixins and classes to provide additional default state.

Type: PlainObject

Defined by ReactiveMixin

goFirst() method

Moves to the first item in the list.

Returns: Boolean True if the current item changed, false if not.

Defined by CursorAPIMixin

goLast() method

Move to the last item in the list.

Returns: Boolean True if the current item changed

Defined by CursorAPIMixin

goNext() method

Move to the next item in the list.

If the list has no current item, the first item will become current.

Returns: Boolean True if the current item changed

Defined by CursorAPIMixin

goPrevious() method

Moves to the previous item in the list.

If the list has no current item, the last item will become current.

Returns: Boolean True if the current item changed

Defined by CursorAPIMixin

ids property

A convenient shortcut for looking up an element by ID in the component's Shadow DOM subtree.

Example: if component's template contains a shadow element <button id="foo">, you can use the reference this[ids].foo to obtain the corresponding button in the component instance's shadow tree. The ids property is simply a shorthand for getElementById, so this[ids].foo is the same as this[shadowRoot].getElementById('foo').

Type: object

Defined by ShadowTemplateMixin

[internal.goFirst]() method

Move to the first item in the set.

Returns: Boolean True if the current item changed, false if not.

Defined by ItemsCursorMixin

[internal.goLast]() method

Move to the last item in the set.

Returns: Boolean True if the current item changed, false if not.

Defined by ItemsCursorMixin

[internal.goNext]() method

Move to the next item in the set.

If no item is current, move to the first item.

Returns: Boolean True if the current item changed, false if not.

Defined by ItemsCursorMixin

[internal.goPrevious]() method

Move to the previous item in the set.

If no item is current, move to the last item.

Returns: Boolean True if the current item changed, false if not.

Defined by ItemsCursorMixin

proxies property

The current set of proxy elements that correspond to the component's main items. If you have assigned elements to the proxy slot, this returns the collection of those elements. Otherwise, this will return a collection of default proxies generated by the component, one for each item.

Type: Array.

proxyListOverlap property

True if the list of proxies should overlap the stage, false if not.

Type: boolean

Default: false

proxyListPartType property

The class or tag used to create the proxy-list part - the list of selectable proxies representing the items in the list.

Type: (component class constructor)|HTMLTemplateElement|string

Default: ListBox

proxyListPosition property

The position of the proxy list relative to the stage.

The start and end values refer to text direction: in left-to-right languages such as English, these are equivalent to left and right, respectively.

Type: 'bottom'|'end'|'left'|'right'|'start'|'top'

Default: 'start'

proxyPartType property

The class or tag used to create the proxy parts - the default representations for the list's items.

Type: (component class constructor)|HTMLTemplateElement|string

Default: 'div'

render(changed) method

Render the indicated changes in state to the DOM.

The default implementation of this method does nothing. Override this method in your component to update your component's host element and any shadow elements to reflect the component's new state. See the rendering example.

Be sure to call super in your method implementation so that your component's base classes and mixins have a chance to perform their own render work.

Parameters:

  • changed: ChangedFlagsdictionary of flags indicating which state members have changed since the last render

Defined by ReactiveMixin

renderChanges() method

Render any pending component changes to the DOM.

This method does nothing if the state has not changed since the last render call.

ReactiveMixin will invoke this method following a setState call; you should not need to invoke this method yourself.

This method invokes the internal render method, then invokes the rendered method.

Defined by ReactiveMixin

rendered(changed) method

Perform any work that must happen after state changes have been rendered to the DOM.

The default implementation of this method does nothing. Override this method in your component to perform work that requires the component to be fully rendered, such as setting focus on a shadow element or inspecting the computed style of an element. If such work should result in a change in component state, you can safely call setState during the rendered method.

Be sure to call super in your method implementation so that your component's base classes and mixins have a chance to perform their own post-render work.

Parameters:

  • changed: ChangedFlags

Defined by ReactiveMixin

selectedIndex property

The index of the selected item, or -1 if no item is selected.

Type: number

Defined by SingleSelectAPIMixin

selectedindexchange event

Raised when the selectedIndex property changes.

Defined by SingleSelectAPIMixin

selectedItem property

The selected item, or null if no item is selected.

Type: Element

Defined by SingleSelectAPIMixin

selectioneffectend event

This event is raised if the current stage applies a transition effect when changing the selection, and the selection effect has completed. CrossfadeStage applies such an effect, for example.

The order of events when the selectedIndex property changes is therefore: selectedindexchange (occurs immediately when the index changes), followed by selectioneffectend (occurs some time later).

setState(changes) method

Update the component's state by merging the specified changes on top of the existing state. If the component is connected to the document, and the new state has changed, this returns a promise to asynchronously render the component. Otherwise, this returns a resolved promise.

Parameters:

  • changes: PlainObjectthe changes to apply to the element's state

Returns: Promise - resolves when the new state has been rendered

Defined by ReactiveMixin

stagePartType property

The class or tag used for the main "stage" element that shows a single item at a time.

Type: (component class constructor)|HTMLTemplateElement|string

Default: Modes

state property

The component's current state.

The returned state object is immutable. To update it, invoke internal.setState.

It's extremely useful to be able to inspect component state while debugging. If you append ?elixdebug=true to a page's URL, then ReactiveMixin will conditionally expose a public state property that returns the component's state. You can then access the state in your browser's debug console.

Type: PlainObject

Defined by ReactiveMixin

stateEffects(state, changed) method

Ask the component whether a state with a set of recently-changed fields implies that additional second-order changes should be applied to that state to make it consistent.

This method is invoked during a call to internal.setState to give all of a component's mixins and classes a chance to respond to changes in state. If one mixin/class updates state that it controls, another mixin/class may want to respond by updating some other state member that it controls.

This method should return a dictionary of changes that should be applied to the state. If the dictionary object is not empty, the internal.setState method will apply the changes to the state, and invoke this stateEffects method again to determine whether there are any third-order effects that should be applied. This process repeats until all mixins/classes report that they have no additional changes to make.

See an example of how ReactiveMixin invokes the stateEffects to ensure state consistency.

Parameters:

  • state: PlainObjecta proposal for a new state
  • changed: ChangedFlagsthe set of fields changed in this latest proposal for the new state

Returns: PlainObject

Defined by ReactiveMixin