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

Class hierarchy:

This element is used as a shadow part in ExpandableSection and PlainExpandableSection.

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

close event

Raised when the component closes.

Defined by OpenCloseMixin

closed property

True if the element is currently closed.

This read-only property is provided as a convenient inverse of opened.

Type: boolean

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

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

effectEndTarget 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 effectEndTarget for details.

Type: HTMLElement

Defined by TransitionEffectMixin

effectphasechange event

Raised when state.effect or state.effectPhase changes.

Note: In general, Elix components do not raise events in response to outside manipulation. (See 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 effectphasechange event whenever the effect or phase changes, even if internal.raiseChangeEvents is false.

Defined by TransitionEffectMixin

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

open() method

Open the element (if not already opened).

Defined by OpenCloseMixin

open event

Raised when the component opens.

Defined by OpenCloseMixin

opened property

True if the element is currently opened.

This property can be set as a boolean attribute

Type: boolean

Default: false

Defined by OpenCloseMixin

openedchange event

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

Defined by OpenCloseMixin

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

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

startEffect(effect) method

See startEffect.

Parameters:

  • effect: string

Defined by TransitionEffectMixin

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 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

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

transitionDuration property

The duration of the expand/collapse transition in milliseconds.

Type: number

Default: {250}

whenClosed() method

This method can be used as an alternative to listening to the "openedchange" 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