ExpandablePanel

Region that expands/collapses in place with an animated transition
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Demo: A region that can be expanded and collapsed

Overview

This component combines OpenCloseMixin, TransitionEffectMixin and a simple CSS height animation.

This component handles only the duties of collapsing and expanding. It does not provide a user interface for the user to trigger the change in state; you must provide that user interface yourself.

API

Ancestry: ExpandablePanel → ReactiveElement → HTMLElement

Built with mixins AttributeMarshallingMixin, EffectMixin, OpenCloseMixin, ReactiveMixin, ShadowTemplateMixin, and TransitionEffectMixin.

This element is used to fill a role in ExpandableSection.

close(closeResult) method

Close the component (if not already closed).

Some components like AlertDialog want to indicate why or how they were closed. To support such scenarios, you can supply a value to the optional closeResult parameter. This closeResult will be made available in the whenClosed promise and the state.closeResult member.

Parameters:

  • closeResult: objectan indication of how or why the element closed

Defined by OpenCloseMixin

closed property

True if the element is currently closed.

Type: boolean

Defined by OpenCloseMixin

closed event

Raised when the component closes.

Defined by OpenCloseMixin

closeFinished property

True if the element has completely closed.

For components not using asynchronous open/close effects, this property returns the same value as the closed property. For elements that have a true value of state.openCloseEffects (e.g., elements using TransitionEffectMixin), this property returns true only if state.effect is "close" and state.effectPhase is "after".

Type: boolean

Defined by OpenCloseMixin

effect-phase-changed event

Raised when state.effect or state.effectPhase changes.

Note: In general, Elix components do not raise events in response to outside manipulation. (See internal.raiseChangeEvents.) However, for a component using TransitionEffectMixin, a single invocation of the startEffect method will cause the element to pass through multiple visual states. This makes it hard for external hosts of this component to know what visual state the component is in. Accordingly, the mixin raises the effect-phase-changed event whenever the effect or phase changes, even if internal.raiseChangeEvents is false.

Defined by TransitionEffectMixin

[internal.defaultState] property

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

Type: State

Defined by ReactiveMixin

[internal.elementsWithTransitions] property

Return the elements that use CSS transitions to provide visual effects.

By default, this assumes the host element itself will have a CSS transition applied to it, and so returns an array containing the element. If you will be applying CSS transitions to other elements, override this property and return an array containing the implicated elements.

See internal.elementsWithTransitions for details.

Type: Array.

Defined by TransitionEffectMixin

[internal.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[internal.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[internal.ids].foo is the same as this.shadowRoot.getElementById('foo').

Type: object

Defined by ShadowTemplateMixin

[internal.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: objectdictionary of flags indicating which state members have changed since the last render

Defined by ReactiveMixin

[internal.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 all internal render methods, then invokes componentDidMount (for first render) or componentDidUpdate (for subsequent renders).

Defined by ReactiveMixin

[internal.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: objectthe changes to apply to the element's state

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

Defined by ReactiveMixin

[internal.startEffect](effect) method

Parameters:

  • effect: string

Defined by TransitionEffectMixin

[internal.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: State

Defined by ReactiveMixin

open() method

Open the element (if not already opened).

Defined by OpenCloseMixin

opened property

True if the element is currently opened.

Type: boolean

Defined by OpenCloseMixin

opened event

Raised when the component opens.

Defined by OpenCloseMixin

opened-changed event

Raised when the opened/closed state of the component changes.

Defined by OpenCloseMixin

toggle(opened) method

Toggle the open/close state of the element.

Parameters:

  • opened: booleantrue if the element should be opened, false if closed.

Defined by OpenCloseMixin

whenClosed() method

This method can be used as an alternative to listening to the "opened-changed" event, particularly in situations where you want to only handle the next time the component is closed.

Returns: Promise A promise that resolves when the element has completely closed, including the completion of any asynchronous opening effect.

Defined by OpenCloseMixin