CenteredStripHighlight

A CenteredStrip that applies a default highlight color to the selected item.

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Demo: CenteredStripHighlight uses a system highlight, much like ListBox

API

$ property

The collection of references to the elements with IDs 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.$.foo to obtain the corresponding button in the component instance's shadow tree.

Such references simplify a component's access to its own elements. In exchange, this mixin trades off a one-time cost of querying all elements in the shadow tree instead of paying an ongoing cost to query for an element each time the component wants to inspect or manipulate it.

These shadow element references are established the first time you read the $ property. They are * not updated if you subsequently modify the shadow tree yourself (to replace one item with another, to add new items with id attributes, etc.).

Type: object

Defined by ShadowTemplateMixin inherited from ReactiveElement

canSelectNext property

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

Type: boolean

Defined by SingleSelectionMixin inherited from CenteredStrip

canSelectPrevious property

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

Type: boolean

Defined by SingleSelectionMixin inherited from CenteredStrip

defaultState property

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

Type: object

Defined by ReactiveMixin inherited from ReactiveElement

indexOfTarget() method

Return the index of the list child that is, or contains, the indicated target node. Return -1 if not found.

Defined by ClickSelectionMixin inherited from CenteredStrip

itemCalcs(item, index) method

Returns a set of calculations about the given item that can be derived from the component's current state.

The goal of the itemCalcs step is to ensure that all mixins/classes use a consistent definition for facts about an item that can be derived from component state. By default, itemCalcs includes a member index containing the index of the indicated item. Other mixins/classes can extend the result of itemCalcs to include additional facts.

For example, the SingleSelectionMixin tracks selection at the component level through a state member state.selectedIndex. When rendering a specific item, a component generally wants to know, "Is this specific item the one which is selected?". SingleSelectionMixin does this with a defintion for itemCalcs that looks like this:

itemCalcs(item, index) {
  const base = super.itemCalcs ? super.itemCalcs(item, index) : null;
  return Object.assign({}, base, {
    selected: index === this.selectedIndex
  });
}

This ensures that any other aspect of the component that wants to inspect the selected state of a given item uses a consistent definition for selection.

Parameters:
  • item: Elementthe item being considered
  • index: numberthe item's position in the list

Defined by ContentItemsMixin inherited from SlotItemsMixin

items property

The current set of items drawn from the element's current state.

Defined by ContentItemsMixin inherited from SlotItemsMixin

itemUpdates(item, calcs, original) method

Determine what updates should be applied to an item to reflect the current state, using the format defined by the updates helpers.

By default, this returns an empty object. You should override this method (or use mixins that override this method) to indicate what updates should be applied to the given item during rendering.

Example: AriaListMixin uses code similar to the following to have an item's aria-selected attribute reflect its selection state:

itemUpdates(item, calcs, original) {
  const base = super.itemUpdates ? super.itemUpdates(item, calcs, original) : {};
  return merge(base, {
    attributes: {
      'aria-selected': calcs.selected
    },
  });
}

This code fragment is intended for use with SingleSelectionMixin, which provides the calcs.selected member.

Returns: object the DOM updates that should be applied to the item

Parameters:
  • item: Elementthe item to be updated
  • calcs: objectper-item calculations derived from element state
  • original: objectthe item's original HTML attributes, classes, and style

Defined by ContentItemsMixin inherited from SlotItemsMixin

refineState(state) method

Apply changes to a proposed new state for the component to enforce necessary consistency between state members. See Refining state for details.

Returns: boolean - true if the state is already acceptable as it is

Parameters:
  • state: objecta proposed new state for the component

Defined by ReactiveMixin inherited from ReactiveElement

render() method

Render the component to the DOM.

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

This method invokes all internal render methods. It then invoked componentDidMount (for first render) or componentDidUpdate (for subsequent renders).

Defined by ReactiveMixin inherited from ReactiveElement

selected-index-changed event

Raised when the selectedIndex property changes.

Defined by SingleSelectionMixin inherited from CenteredStrip

selectedIndex property

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

Type: number

Defined by SingleSelectionMixin inherited from CenteredStrip

selectedItem property

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

Type: Element

Defined by SingleSelectionMixin inherited from CenteredStrip

selectFirst() method

Select the first item in the list.

Returns: Boolean True if the selection changed, false if not.

Defined by SingleSelectionMixin inherited from CenteredStrip

selectionRequired property

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

Type: boolean

Default: false

Defined by SingleSelectionMixin inherited from CenteredStrip

selectionWraps property

True if selection navigations wrap from last to first, and vice versa.

Type: boolean

Default: false

Defined by SingleSelectionMixin inherited from CenteredStrip

selectLast() method

Select the last item in the list.

Returns: Boolean True if the selection changed, false if not.

Defined by SingleSelectionMixin inherited from CenteredStrip

selectNext() method

Select the next item in the list.

If the list has no selection, the first item will be selected.

Returns: Boolean True if the selection changed, false if not.

Defined by SingleSelectionMixin inherited from CenteredStrip

selectPrevious() method

Select the previous item in the list.

If the list has no selection, the last item will be selected.

Returns: Boolean True if the selection changed, false if not.

Defined by SingleSelectionMixin inherited from CenteredStrip

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.

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

Parameters:
  • changes: objectthe changes to apply to the element's state

Defined by ReactiveMixin inherited from ReactiveElement

shouldComponentUpdate(nextState) method

Return true if the component should update.

The default implementation does a shallow check of property values like React's PureComponent. This seems adequate for most web components. You can override this to always return true (like React's base Component class), or to perform more specific, deeper checks for changes in state.

Returns: boolean - true if the component should update (rerender)

Parameters:
  • nextState: objectthe proposed new state for the element

Defined by ReactiveMixin inherited from ReactiveElement

state property

The component's current state. The returned state object is immutable. To update it, invoke setState.

Type: object

Defined by ReactiveMixin inherited from ReactiveElement

updates property

The attributes and properies that should be applied to the component on render. By default, this is an empty plain object. Your mixin or component can extend this to identify the properties to set on the host element or elements in the shadow subtree.

Type: object

Defined by RenderUpdatesMixin inherited from ReactiveElement

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