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APL Base Component Properties

(This is not the most recent version of APL. Use the Other Versions option to see the documentation for the most recent version of APL)

A component is a primitive element that displays on the viewport.

In APL, components are primitive visual components rendered by the client. Although you can add the definition of new templates by creating APL files and importing them into other APL, new low-level components would require updates to the clients to be able to recognize and convert them to native user interface controls on devices.

Properties

The standard properties in a component are as follows. In general, any property related to dimensions cannot be used to provide padding for components.

Property Type Required Styled Dynamic Description
bind Array of bindings No No No Expressions to add to the data binding context.
entity (entities) Array of entities No No No Opaque data used to clarify references in Alexa.
height Dimension No No Read-only Requested height of the component. Defaults to auto.
id String No No No Reference name of the component, used for navigation and events. Required if the component is used with standard built-in intents.
inheritParentState Boolean No No No If true, use the parent's state.
maxHeight Dimension No No No Maximum allowed height of this component. Defaults to none.
maxWidth Dimension No No No Maximum allowed width of this component. Defaults to none.
minHeight Dimension No No No Minimum allowed height of this component. Defaults to 0.
minWidth Dimension No No No Minimum allowed width of this component. Defaults to 0.
paddingBottom Dimension: Properties No No No Space to add to the bottom of this component. Defaults to 0.
paddingLeft Dimension: Properties No No No Space to add to the left of this component. Defaults to 0.
paddingRight Dimension: Properties No No No Space to add to the right of this component. Defaults to 0.
paddingTop Dimension: Properties No No No Space to add to the top of this component. Defaults to 0.
style Style No No No Named style or styles to apply.
type String Yes No No Type of the component. Required.
when Boolean No No No If the expression with when evaluates to false, this component is not inflated or selected. Defaults to true.
width Dimension: Properties No No Read-only Requested width of this component. Defaults to auto.

bind

The bind property of a component extends the data-binding context for the component and its children. The bind property also specifies an ordered set of data-bindings that extend the current context. Bindings are ordered, and later bindings may use previous definitions.

bind properties

Each binding object in the binding array contains the following properties

Property Type Required Description
name String Yes Name to use for this binding. Must be a valid name.
value Any Yes Value to assign to this binding. If a string, data-binding will occur on the contents of the string.
type Type No Property type. Defaults to any.

bind evaluation

The bind property evaluates after the when property and before any other properties. In other words, the when expression cannot rely on the new bindings, but other properties of this component may rely on the bindings. For example:

{
"type": "Text",
"bind": [
{ "name": "foo", "value": "27" },
{ "name": "bar", "value": "${foo + 23}" }
],
"text": "The value of bar is ${bar}"
}

In this example, foo and bar augment the data-binding context. The final text will be "The value of bar is 2723" because the addition of a string and an integer results in an implicit cast to string.

entity

Opaque entity data. Alexa devices pass the entity data back to the skill as context.

height and width

The properties width, height, minWidth, minHeight, maxWidth, and maxHeight are dimensional properties.

Minimum width and height values default to 0, which means the component can disappear. Maximum width and height properties default to none, which indicates that the component can scale arbitrarily. If unspecified, the width and height values will revert to the component's natural size.

id

A developer-assigned value used to locate a particular component in the view hierarchy. Although recommended, the id is not required to be unique.

inheritParentState

Replaces the component state with the state of the parent of the component. Used for components that need to visually change appearance based on the state of the parent. For example, you may want a Text component inside of a TouchWrapper to change color when the TouchWrapper is pressed. By setting inheritParentState, the Text component will change state whenever the TouchWrapper changes state.

paddingBottom, paddingLeft, paddingRight, and paddingTop

Padding values are dimensions that add space around a component. APL uses the border-box model for calculating the total width and height of an element. Default for each is 0.

style

The style is a named style. If no style is assigned, the component will use a platform-defined internal style.

type

Specifies the particular component to inflate. It can be one of the primitive components listed in this section or can be a named layout.

when

If the when expression is true, inflate the component. If false, ignore the component and all child components.