PullToRefresh

Lets the user refresh content with a swipe down gesture
OVERVIEW | USAGE | API
Demo: Open this in a separate window on a mobile device ⇲

Overview

PullToRefresh implements a common touch user interface pattern in which the user can swipe down in order to refresh content.

Note: The above demo includes sound that will play on Chrome (but not Safari). The sound is defined by the demo and not the PullToRefresh component. The component provides no sound of its own.

Usage

import PullToRefresh from 'elix/define/PullToRefresh.js';
const pullToRefresh = new PullToRefresh(); // or
const pullToRefresh = document.createElement('elix-pull-to-refresh');

In HTML:

<script type="module" src="node_modules/elix/define/PullToRefresh.js"></script>
<elix-pull-to-refresh>
  <!-- Content that can be refreshed goes here. -->
</elix-pull-to-refresh>

Use PullToRefresh when:

  • You present time-indexed content in reverse chronological order (newest items at the top).
  • The content is changing frequently.
  • Vertical space is at a premium. If you have sufficient room, a Refresh button may be a simpler and more self-evident way to let users refresh content.

API

Class hierarchy:

PlainPullToRefresh
PullToRefresh component in the Plain reference design system
PullToRefresh
Lets the user refresh content with a swipe down gesture
Built with EffectMixin • TouchSwipeMixin
ReactiveElement
General-purpose base for writing components in functional-reactive style
Built with AttributeMarshallingMixin • ReactiveMixin • ShadowTemplateMixin
HTMLElement
Standard browser class for all custom elements

The element defines the following shadow parts:

  • indicator: either of the pull or refreshing indicators
  • indicator-container: container for the refreshing indicators
  • pull-indicator: the element shown to let the user know they can pull down, default type is div element
  • refresh-header: the header area shown when the user pulls down
  • refreshing-indicator: the element shown during a refresh of the content, default type is div element

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

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

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

pullIndicatorPartType property

The class or tag used to create the pull-indicator part – the element that lets the user know they can pull to refresh.

By default, this is a down arrow icon.

Type: (component class constructor)|HTMLTemplateElement|string

refreshingchange event

Raised when the refreshing state changes.

refreshingIndicatorPartType property

The class or tag used to create the refreshing-indicator part – the element shown to let the user know the element is currently refreshing.

Type: (component class constructor)|HTMLTemplateElement|string

Default: ProgressSpinner

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: ChangedFlags – dictionary 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: PlainObject – the changes to apply to the element's state

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

Defined by ReactiveMixin

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: PlainObject – a proposal for a new state
  • changed: ChangedFlags – the set of fields changed in this latest proposal for the new state

Returns: PlainObject

Defined by ReactiveMixin

swipeTarget property

See swipeTarget.

Type: HTMLElement

Defined by TouchSwipeMixin