APL Standard Commands (APL 1.2)

(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)

• Common Properties
• AnimateItem Command
• AutoPage command
• Idle command
• OpenURL Command
• Parallel command
• Scroll command
• ScrollToComponent Command
• ScrollToIndex command
• SendEvent command
• Sequential command
• SetFocus Command
• ClearFocus Command
• SetPage command
• SetState Command
• SetValue Command
• SpeakItem command
• SpeakList Command
• Related topics

See also: APL Commands and APL Media Commands.

Common Properties

A single command is encoded as a JSON object. All commands contain the following properties.

type

Specifies the particular command to run. This may be a pre-defined primitive command types or a user-defined command.

delay

The delay value is the amount of time in milliseconds inserted before running this command. The delay value must be a non-negative integer, which if not specified, defaults to 0. The delay value is ignored if the when property resolves to false, or if the command runs from within an event handler.

screenLock

If true, the interaction timer is disabled while this command runs. When a command with screenLock=true finishes running, the interaction timer is reset to 0.

The screenLock applies to the entire extent of the command including any defined delay. For example, the following command holds the screen lock for 30 seconds:

{
  "type": "Idle",
  "delay": 30000,
  "screenLock": true,
}

when

If when is set to true, run the command. If false, ignore the command. Commands that are ignored also ignore the screenLock property.

AnimateItem Command

AnimateItem requires APL 1.1 or later. Provide an alternate experience for devices running older versions of APL.

Runs a fixed-duration animation sequence on one or more properties of a single component. For example:

{
  "type": "AnimateItem",
  "easing": "ease-in-out",
  "duration": 600,
  "componentId": "myFlyingComponent",
  "value": [
    {
      "property": "opacity",
      "to": 1
    },
    {
      "property": "transform",
      "from": [
        {
          "translateX": 200
        },
        {
          "rotate": 90
        }
      ],
      "to": [
        {
          "translateX": 0
        },
        {
          "rotate": 0
        }
      ]
    }
  ]
}

Components support animating opacity and transform properties. The from value does not need to be specified for opacity, but it does need to be specified for transforms.

To define a custom easing curve, you can write:

{
  "type": "AnimateItem",
  "easing": "path(0.25, 0.6, 0.5, 0.8, 0.75, 0.9)",
  "duration": 1000,
  "value": {
    "property": "opacity",
    "to": 1
  }
}

AnimateItem defines the following properties in addition to normal command properties:

In fast mode, the AnimateItem command jumps ahead to the end state of the animation. When an AnimateItem command stops, the animation jumps ahead to the end state; refer to repeatMode for a discussion of how to calculate the end state.

componentId

The ID of the component. If omitted, the component issuing the AnimateItem command is used.

duration

The duration in milliseconds of a single pass of the animation. If the repeatCount property is set to greater than 0, the total duration of the animation will be the product of the duration and one more than the repeat count. For example, the following animation will have a total duration of 10 seconds:

{
  "type": "AnimateItem",
  "duration": 1000,
  "repeatCount": 9,
  "repeatMode": "reverse",
  "value": {
    "property": "opacity",
    "from": 0,
    "to": 1
  }
}

easing

An easing curve specifies how the value of the parameter changes over time. The curve must be a function starting at (0,0) and ending at (1,1). Two standard general ways of writing an easing curve are defined:

1. cubic-bezier(x1,y1,x2,y2): Following the CSS standard, this defines a cubic Bézier curve with starting point (0,0) and ending point (1,0). The parameterized values (x1, y1) and (x2, y2) defined the interior control points of the curve and are normally between 0 and 1.
2. path(x1,y1,...,xN,yN): A linear-piecewise function from (0,0) to (1,1). The x values must be in ascending order and between 0 and 1; the y values may be arbitrary. The end values of (0,0) and (1,1) are implicit.

The following easing curves are pre-defined:

repeatCount

The repeatCount defines how many times an animation will repeat before the command ends. By default, the repeatCount is set to 0; the animation will play through once and stop.

repeatMode

The repeateMode defines whether animations will be played from start to finish each time or if the animation will play backwards to the start each alternative time. The following repeat modes are defined:

The end state of an animation is a function of the repeatCount and repeatMode. If the repeatMode is reverse and the repeatCount is an odd number, the animation end state will be the same as its starting state. In all other cases the end state will be the "natural" end state assigned as the to value.

A prematurely stopped animation always "jumps" to its end state.

value

The array of animated properties. Each element in the array has the following form:

A property animation is defined by the to/from properties or the inputRange/outputRange properties. If you don't specify a "from" value, the current value of the property is used.

There are a few special cases to consider with the transform property. First, the transform property does not implicitly define a from property; both the from and to properties must be set.

Second, interpolating between smoothly between transformations requires that the same series of transformation operations appear in the from list and the to list and in the same order. For example:

"from": [ { "translateX": 30 }, { "rotate": 90 }],
"to": [ { "translateY": 30 }, { "rotate": 45 }]

is a valid from/to transformation because each array contains a translation followed by a rotation. A non-working example:

"from": [ { "translateX": 30 }, { "scale": 1 }, { "rotate": 90 }],
"to": [ { "scale": 2 }, { "rotate": 45 }]

In this case the arrays don't match; they have different lengths and the first element differs between the arrays. The APL author may expect the system to automatically fill in the "missing" { "translateX": 0 } transformation at the start of the to array, but the APL runtime is not clever enough to automatically find and fix the difference.

AutoPage command

The AutoPage command automatically progresses through a series of pages displayed in a Pager component. The AutoPage command finishes after the last page has been displayed for the requested time period.

The AutoPage command has the following properties in addition to the regular command properties.

For example, to auto-page through a Pager called mySportsPager:

  {
    "type": "AutoPage",
    "componentId": "mySportsPager",
    "duration": 1000,
    "delay": 500
  }

The above example first pauses for 500 milliseconds (the delay property), then advances to the next page, pauses for 1000 milliseconds (the duration property), and continues advancing and pausing until the final pause has completed. For example, if mySportsPager has three pages and initially displays page 1, then AutoPage does the following:

• Displays page 1 for 500ms while waiting to start.
• Changes to page 2 and pauses for 1000ms.
• Changes to page 3 and pauses for 1000ms.

At this point the command is complete, so the Pager continues to display page 3 until another command or event causes a change.

The AutoPage command has no effect if the count is non-positive.

When stopped, the AutoPage command:

• Moves the display ahead to the target page if the AutoPage command sequence is at least 50% complete.
• Returns the display to the previous page if it is not at least 50% complete.

The onPageChange command is run once with the new page if the page has changed

The AutoPage command is ignored in fast mode.

componentId

The identifier of the Pager component. If omitted, the component issuing the AutoPage command is used.

count

The number of pages to display. If not specified, this defaults to the number of pages remaining. Wrapping is not supported; the count is internally clipped to fall in the range [0, pager.children.length - pager.currentIndex - 1].

duration

The amount of time to wait after advancing to the next page. Any animated transition between pages is not included in the duration and hence will increase the overall command run time.

Since the duration is applied after advancing to the next page, it does not apply to the first page of the pager. To delay the start of paging, use the standard command delay property.

Idle command

The Idle command does nothing. Use as a placeholder or to insert a calculated delay in a longer series of commands. For example, consider this command.

  {
    "type": "Parallel",
    "commands": [
      {
        "type": "Idle",
        "delay": 3000
      },
      {
        "type": "SpeakItem",
        "componentId": "item7"
      }
    ]
  }

This command sequence speaks "item7". The use of the Idle command guarantees that the overall command will last at least 3000 milliseconds even if the speech ends earlier.

The type of the Idle command is Idle.

The idle command is ignored in fast mode

OpenURL Command

OpenURL requires APL 1.1 or later. Provide an alternate experience for devices running older versions of APL.

Open a URL. The OpenURL command, if successful, opens the specified URL in a web browser or other application on the device. You must provide a suitable URL that works on the current device. The OpenURL command has the following properties in addition to the regular command properties:

For example, to open the Amazon home page in the browser on the device:

{
  "type": "OpenURL",
  "source": "https://www.amazon.com/",
  "onFail": {
    "type": "SetValue",
    "componentId": "errorText",
    "property": "text",
    "value": "Unable to open Amazon.com (${event.source.value})"
  }
}

Not all devices support opening a URL. If the device does not support opening URLs, the command is ignored and it does not run onFail commands. Check the value of the allowOpenURL in the data-binding context to determine if OpenURL is supported on the device.

The OpenURL command is ignored in fast mode.

source

The source property is a URL/URI suitable for launching an application on the local device. It may also be used with the http or https schema to open a web page in the local web browser.

onFail

The onFail property contains one or more commands to run if the URL cannot be opened. There is no guarantee that the onFail command will run within a time limit or that it will appear to be successful to the end user; for example, a URL could open a blank or error web page. However, the APL runtime should try to report failure within three seconds. The event generated for the onFail command has the following form:

"event": {
  "source": {
    "source": "OpenURL",
    "handler": "Fail",
    "value": NUMBER    // Platform-defined numerical error
  }
}

The event.source.value field passed to the onFail command will be set to a platform-defined numerical error code. This error code is not suitable for showing to the user (despite the example provided above), but may be used to send failure information back to the cloud skill through a SendEvent command.

Parallel command

Run a series of commands in parallel. The Parallel command starts running all child commands simultaneously. The Parallel command is considered finished when all of its child commands have finished. When the Parallel command stops early, all currently running commands stop.

The type of the Parallel command is Parallel. The Parallel command has the following properties in addition to the common command properties.

In fast mode, the parallel command runs all of the sub-commands in parallel, but without delays (giving a net zero duration)

commands

An un-ordered array of commands to run in parallel. After all commands have finished running, the Parallel command finishes. The delay value set for the Parallel command is added to the delay value set for each of the commands in the array. In the following example, the first SendEvent command runs at 1500 milliseconds, and the second SendEvent command at 750 milliseconds, which means the second SendEvent command begins to run before the first.

{
  "type": "Parallel",
  "delay": 500,
  "commands": [
    {
      "type": "SendEvent",
      "delay": 1000
    },
    {
      "type": "SendEvent",
      "delay": 250
    }
  ]
}

Scroll command

The Scroll command scrolls a ScrollView or Sequence forward or backward by a set number of pages. The Scroll command has the following properties in addition to the regular command properties.

The distance sets how far to scroll, in pages. For example, to scroll a list forward a single page:

  {
    "type": "Scroll",
    "componentId": "myScrollingList",
    "distance": 1
  }

Scrolling stops when:

• The destination is reached.
• The end of the scrollable content is reached.
• The user touches the screen.
• Alexa sends a new command. Starting a new command ends the Scroll command, which stops scrolling immediately.

To smoothly scroll through all available content, set the distance to a large number. For example, to smoothly scroll back to the beginning of a list:

  {
    "type": "Scroll",
    "componentId": "myScrollingList",
    "distance": -10000
  }

The Scroll command is ignored in fast mode.

componentId

The ID of the ScrollView or Sequence. If omitted, the component issuing the ScrollPage command is used.

distance

The scrolling distance, measured in pages. One "page" is the width or height of the ScrollView or Sequence, less any applied padding. Negative numbers scroll backwards. Setting distance to 0 does not scroll.

For example consider a ScrollView with a height of 400dp and 50dp of padding on the top and bottom. A "page" of the ScrollView is 300dp. Specifying a distance of 0.5 will scroll forward by 50% of the page, or 150dp.

The distance may also be expressed as a relative or absolute dimension with a suitable suffix; for example, "50%", "33dp", or "25vh". Note that setting the distance to a relative number (e.g. "50%") is exactly equal to using a simple number (in this case, 0.5). Because APL documents are commonly written to adjust to the size of the screen it is preferable to use relative scrolling dimensions such as "50%" or 0.5 over using absolute dimensions such as "100dp". This ensures that the content will scroll a sensible distance for the user no matter what device it is displayed on.

ScrollToComponent Command

Scroll forward or backward through a ScrollView or Sequence to ensure that a particular component is in view. The ScrollToComponent command has the following properties in addition to the regular command properties.

For example, to scroll to ensure a particular item is in view:

{
  "type": "ScrollToComponent",
  "componentId": "recipeSteps",
  "align": "center"
}

The ScrollToComponent command looks for the first Sequence or ScrollView at or above the componentId and scrolls that one.

Scrolling stops if the user touches the screen. Stopping the command stops scrolling immediately.

The ScrollToComponent command is ignored in fast mode.

align

The alignment of the item on the screen after scrolling and before speech. Alignment is an enumerated value with the following options:

componentId

The ID of component. If omitted, the component issuing the ScrollToComponent command is used.

ScrollToIndex command

Scroll forward or backward through a ScrollView or Sequence to ensure that a particular child component is in view. The ScrollToIndex command has the following properties in addition to the regular command properties.

For example, to scroll to show the fifth step in a recipe displayed in a list, set index to 4.

  {
    "type": "ScrollToIndex",
    "componentId": "recipeSteps",
    "index": 4,
    "align": "center"
  }

The componentId does not have to be a Sequence or ScrollView component. The ScrollToIndex command looks for the first Sequence or ScrollView at or above the componentId and scrolls that one.

Scrolling stops if the user touches the screen. Stopping the command stops scrolling immediately.

The ScrollToIndex command is ignored in fast mode.

align

The alignment of the item on the screen after scrolling and before speech. Alignment is an enumerated value with the following options.

componentId

The identifier of the parent container. If omitted, the component issuing the ScrollToIndex command is used.

index

The 0-based index of the child item in the parent container to scroll into view. Negative values are measured from the end of the parent container. For example, to show the second-to-last item in a list:

  {
    "type": "ScrollToIndex",
    "index": -2,
  }

The algorithm for finding the item to display can be described loosely as follows:

  let itemIndex = index < 0 ? index + children.length : index;
  if (itemIndex >= 0 && itemIndex < children.length) {
    let child = children[itemIndex];
    scrollIntoView(child);
  }

SendEvent command

Use the SendEvent command to generate and send an event to Alexa. The SendEvent command sends a UserEvent request to your skill. Information about the components and events that triggered the command is included in the UserEvent.

The following example illustrates a SendEvent command on the onPress handler of a TouchWrapper.

{
  "type": "TouchWrapper",
  "id": "idForTheTouchWrapper",
  "spacing": "@spacingSmall",
  "alignSelf": "center",
  "onPress": [
    {
      "type": "SendEvent",
      "arguments": [
        "textWasPressed",
        "Send this data to the skill"
      ],
      "components": [
        "idForTheTextComponent"
      ]
    }
  ],
  "item": {
    "type": "Text",
    "id": "idForTheTextComponent",
    "color": "@colorAccent",
    "text": "Click to send a UserEvent to the skill."
  }
}

SendEvent has the following properties in addition to the regular command properties.

The SendEvent command is ignored in fast mode.

arguments

An array of data to send to the skill in the UserEvent request. Data binding applies to each element in the array when SendEvent runs. This allows an argument to contain data about the event itself, such as ${event.source.value}. Use this to send arbitrary data to your skill.

Access this data in your UserEvent handler in the arguments property of the request.

components

The components property is an array of component IDs. The value of each of these components is included the UserEvent request. You can use this to construct a form where the contents of the form are sent directly to the server.

Access the component values in the components property of the request.

UserEvent

The SendEvent command sends the skill an Alexa.Presentation.APL.UserEvent request.

For example, the SendEvent defined in the TouchWrapper shown earlier generates the following UserEvent request.

{
  "type": "Alexa.Presentation.APL.UserEvent",
  "requestId": "amzn1.echo-api.request.1",
  "timestamp": "2020-01-20T22:28:44Z",
  "locale": "en-US",
  "arguments": [
    "textWasPressed",
    "Send this data to the skill"
  ],
  "components": {
    "idForTheTextComponent": "Click to send a UserEvent to the skill."
  },
  "source": {
    "type": "TouchWrapper",
    "handler": "Press",
    "id": "idForTheTouchWrapper"
  },
  "token": "token-provided-with-RenderDocument"
}

This UserEvent includes the following information defined in the SendEvent command:

• The arguments property contains an array containing the data passed to the arguments array of the SendEvent command. In this example, these are static strings, but you could use data-binding to include dynamic information here.
• The source property includes details about the component that triggered the event. In this example, this is the TouchWrapper.
• The components property contains the value of the component with the ID "idForTheTextComponent". Since this is a Text component, the value included in the UserEvent is the value of the text property. This is included because the SendEvent included this same ID in the components array.

For more details about the UserEvent request, see UserEvent request.

For an example of a UserEvent handler, see Handle a UserEvent request.

Sequential command

The Sequential command runs a series of commands in order, waiting for the previous command to finish before starting the next. The Sequential command finishes when all of its child commands have finished.

The type of the Sequential command is Sequential. The Sequential command has the following properties in addition to the common command properties.

• In normal mode the commands run in order, followed by the finally commands. The repeatCount only applies to the regular commands.
• In fast mode the commands run in order without repeating, followed by the finally commands.
• If one of the commands stops early (in normal mode), the catch commands and finally commands run in fast mode.
• If one of the finally commands stops while running in normal mode, the remaining finally commands run in fast mode.

catch

catch requires APL 1.1 or later. Provide an alternate experience for devices running older versions of APL.

The catch commands run if the Sequential command stops due to another command running. The catch commands run in "fast" mode – that is, all durations are ignored and commands jump to their final values. The catch commands run before any finally commands.

The catch commands run one time. The repeatCount property doesn't apply to catch commands.

commands

An array of commands to run. The array of commands run in order, and each command must finish before the next one can begin. The delay value of the Sequential command and the delay value of the first command in the sequence are additive. In the following example, the first SendEvent command runs after 3000 milliseconds.

{
  "type": "Sequential",
  "delay": 1000,
  "repeatCount": 2,
  "commands": [
    {
      "type": "SendEvent",
      "delay": 2000
    },
    {
      "type": "SendEvent",
      "delay": 2000
    }
  ]
}

finally

finally requires APL 1.1 or later. Provide an alternate experience for devices running older versions of APL.

The finally commands run after the normal sequential commands finish or after the catch commands run due to the command stopping early. The finally commands run in normal mode unless (a) the entire Sequential command ran in fast mode or (b) the sequential command stopped early.

The finally commands run one time. The repeatCount property doesn't apply to finally commands.

repeatCount

The number of times to repeat this series of commands. Defaults to 0. Negative values will be ignored.

SetFocus Command

SetFocus requires APL 1.1 or later. Provide an alternate experience for devices running older versions of APL.

Changes the actionable component that is in focus. See Focused for the actionable components that can receive and lose focus.

Only one component has focus at a time. Setting the focus on a component automatically clears it from other components.

When SetFocus runs, the command does the following:

1. Places the targeted component into focus and sets that focused state to true.
2. Removes focus from any component that had it before and sets that component's focused state to false.

The SetFocus command is ignored if the targeted component is disabled, not actionable, or has the inheritParentState property set to true.

The SetFocus command has the following properties in addition to the standard command properties.

For example, to focus a specific component with the id myButton:

{
  "type": "SetFocus",
  "componentId": "myButton"
}

The SetFocus command runs in fast mode, but without any delay.

componentId

The ID of the component which will receive focus. If this property is omitted, the component issuing the SetFocus command is the recipient.

To open a document with a component in focus, set the document onMount property to SetFocus.

For example, to focus a specific component on document mount:

{
  "onMount": {
    "type": "SetFocus",
    "componentId": "myButton"
  }
}

ClearFocus Command

ClearFocus requires APL 1.1 or later. Provide an alternate experience for devices running older versions of APL.

Removes focus from the actionable component that is currently in focus. See Focused for the actionable components that can receive and lose focus.

Only one component may have focus at a time, so ClearFocus only ever affects one component.

When ClearFocus runs, the command removes focus from the component that has it, and sets that component's focused state to false.

The ClearFocus command has no additional properties to the regular command properties.

For example, to clear focus from any component that has it:

{
  "type": "ClearFocus"
}

The ClearFocus command runs in fast mode, but without any delay.

SetPage command

The SetPage command changes the page displayed in a Pager component. The SetPage command finishes when the item is fully in view. The SetPage command has the following properties in addition to the regular command properties.

When there are N pages in the Pager component, the first is index 0 and the last has index N-1. A relative position offsets from the current page. For example, to move one page forward:

  {
    "type": "SetPage",
    "componentId": "myWeatherPager",
    "position": "relative",
    "value": 1
  }

An absolute position sets the index of the current page. A negative absolute position is an offset from the end of the list. For example, to go to the last page:

  {
    "type": "SetPage",
    "componentId": "myWeatherPager",
    "position": "absolute",
    "value": -1
  }

No intermediate pages display when switching between two pages (unlike a Sequence). For example, if the current page is 13 and SetPage runs with "position"="relative","value": 2, the current page will transition out and page 11 will transition in without showing page 12.

The SetPage command can set any page for display. It does not respect the allowed navigation direction in the Pager component. However, wrapping behavior affects page switch calculations, as shown in approximate algorithm.

Stopping a SetPage command jumps ahead to the target page if the SetPage command sequence is at least 50% complete, and it returns to the previous page if it is not at least 50% complete. The onPageChange command runs one time when the command stops if the page has changed from the last page.

The SetPage command is ignored in fast mode.

componentId

The identifier of the Pager component. If omitted, the component issuing the SetPage command is used.

position

If the position is relative, the value is a relative distance to move from the current page. If the position is absolute, the value is the absolute page number to which the display will move.

value

The value is either the distance to move or the absolute page number to move to.

The algorithm to calculate final position and direction can be approximated with this pseudo-code.

  if (command.position == 'absolute') {  // Absolute motion
    let index = command.value < 0 ? pager.children.length + command.value : command.value;
    index = Math.max(0, Math.min(pager.children.length - 1, index));  // Clamp range

    // Return the final index and the direction of motion
    if (index == pager.currentIndex)
      return NO_MOVE

    return (index, index < pager.currentIndex ? "LEFT" : "RIGHT");
  }
  else {  // Relative motion
    let index = pager.currentIndex + command.value;

    // If relative motion goes out of bounds and we don't support wrapping, ignore the command
    if (pager.navigation != "wrap" && (index < 0 || index >= pager.children.length))
      return NO_MOVE;

    // Wrap appropriately
    index = ((index % pager.children.length) + pager.children.length) % pager.children.length;
    if (index == pager.currentIndex)
       return NO_MOVE;

    return (index, command.value < 0 ? "LEFT" : "RIGHT");
  }

The pager animation is driven by the returned direction.

This algorithm has these characteristics:

• Absolute values clamp within the valid range of pages. The direction is relative to the current page.

• Relative values on a wrapping pager will wrap arbitrarily. The direction is based on the commanded value, and wrapping doesn't change the direction.

• Relative values on a non-wrapping pager that go out of range are ignored.

SetState Command

This command is deprecated, and no longer the correct way to change state.

Use SetValue, SetFocus, and ClearFocus to change the disabled, checked, and focused states respectively. See Component state for details.

Each component has a state used to evaluate styles and displaying the component. The SetState command changes one of the component's state settings.

The SetState command can be used to change the checked and disabled, but it is not recommended. Use SetValue to change the checked and disabled properties, which updates the state.

You cannot directly set the focused, karaoke, karaokeTarget, and pressed states. Use the SetFocus, ClearFocus, or SpeakItem commands to change those states.

The SetState command has the following properties in addition to the regular command properties.

This example sets a TouchWrapper to the checked state.

{
  "type": "SetState",
  "componentId": "myButton",
  "state": "checked",
  "value": true
}

componentId

The identifier of the component whose state will change. If this property is omitted, then the component that issues the SetState command is the recipient.

state

The name of the state to change. Currently restricted to checked, disabled, and focused.

value

The value evaluates when the command runs, so it can take advantage of existing component properties. For example, this command toggles the checked state of the current component.

{
  "type": "SetState"
  "state": "checked",
  "value": "${!event.source.value}"
}

SetValue Command

Changes a property or binding of a component. Each component has a defined set of dynamic properties that can be changed with SetValue. Each component also may have named bindings. Refer to the specifics of each component for the dynamic properties you can change with SetValue.

The SetValue command has the following properties in addition to the regular command properties.

This example sets a value so that the punchline for a joke appears, because an opacity value of 1 means the component is fully visible.

{
  "type": "SetValue",
  "componentId": "jokePunchline",
  "property": "opacity",
  "value": 1
}

The SetValue command changes the value of a component property or component binding. The following rules are followed:

1. If the component has a property named property that is dynamic, then the property is updated with the new value.
2. Otherwise, if the component has a bind property with that name, then that bound property will be updated.
3. If a bound property changes value, then all dynamic properties of components that depend on that property will be updated.

An example of updating a binding value:

{
  "type": "TouchWrapper",
  "bind": [
    {
      "name": "MyCounter",
      "value": 0,
      "type": "number"
    }
  ],
  "item": {
    "type": "Text",
    "text": "You have pressed the button ${MyCounter} times"
  },
  "onPress": {
    "type": "SetValue",
    "property": "MyCounter",
    "value": "${value + 1}"
  }
}

In the above example, each time you press the TouchWrapper, the text displayed increments.

The SetValue command runs in fast mode, but without any delay.

componentId

The identifier of the component whose value will change. If this property is omitted, then the component that issues the SetValue command is the recipient.

property

The name of the property to change. This may be a built-in property or a binding.

value

The value evaluates when the command runs, so it can take advantage of existing component properties. In this example, the SetValue command sets the opacity of the target component to 50% of its actual value.

{
  "type": "SetValue"
  "property": "opacity",
  "value": "${event.target.opacity * 0.5}"
}

SpeakItem command

The SpeakItem command reads the contents of a single item on the screen. The item will scroll into view if it is not currently visible. The item should have a speech property, but it is not required. Any type of component can be the recipient of SpeakItem.

The SpeakItem command has the following properties in addition to the regular command properties.

For example, to read the contents of a single text component and ensure it is aligned in the center of the screen:

  {
    "type": "SpeakItem",
    "componentId": "myJokeSetup",
    "highlightMode": "line",
    "align": "center"
  }

The karaoke state of the component is set to true during the speech and reset to false after the speech completes. The highlightMode only applies to Text components. When a Text component is read in "highlightMode": "line" mode, individual lines of text are set to the karaoke state during speech and reset to false after speech completes.

Note these restrictions:

• The SpeakItem command does not scroll the content during speech in block mode. For example, if the component is larger than the scrolling container of the component, those parts of the component that are not visible after scrolling will remain hidden.

• Components on round screens should use center alignment, or much of the content will not be visible.

• SpeakItem does not highlight individual words or lines of text during speech when highlightMode is block.

• The algorithm used to scroll the item into view assumes there is only a single scrolling component. Nested scrolling components are not supported.

• Components without a speech property will still scroll into view.

When a SpeakItem command stops early, it clears any visual changes and stops speech immediately.

The SpeakItem command is ignored in fast mode.

align

The alignment of the item on the screen after scrolling and before speech. Alignment is an enumerated value with the following options.

componentId

The ID of the spoken component. If omitted, the component issuing the SpeakItem command is used.

highlightMode

Controls how contents of a Text component are styled during speech. If set to "block", the entire Text component has the karaoke state set to true during speech. If highlightMode is set to "line", the individual lines of the Text component are treated separately. Each line will scroll to match the align property and be styled separately.

In line-by-line karaoke mode, the only styling change accepted is the color property; other properties are ignored.

When a component other than a Text component is the recipient of SpeakItem, the highlightMode is ignored.

minimumDwellTime

The minimum amount of time in milliseconds to highlight an item.

SpeakList Command

Read the contents of a range of items inside a common container. Each item will scroll into view before speech. Each item should have a speech property, but it is not required.

The SpeakList command has the following properties in addition to the regular command properties.

The minimumDwellTime prevents items with short titles from being read too quickly. For example, a series of movie titles like "Venom", "Fences", and "Dear Zachary: A Letter to a Son About His Father" needs some dwell time for the first two items.

This example reads three components out of the middle of a list and ensures that each aligns in the center of the screen:

{
  "type": "SpeakList",
  "componentId": "movieList",
  "start": 3,
  "count": 3,
  "minimumDwellTime": 700,
  "align": "center"
}

The karaoke state of the component is set to true during the speech of each component and reset to false after that speech completes.

Note these characteristics of the SpeakList command:

• The SpeakList command does not scroll the content during speech. For example, if the component is larger than the scrolling container of the component, those parts of the component that are not visible after scrolling will remain hidden.
• Components on round screens should use center alignment, or much of the content will not be visible.
• SpeakList does not highlight individual words or lines of text during speech.
• To scroll the item into view, the component hierarchy is searched upwards to find the first ancestor that can be scrolled.
• The algorithm that used to scroll the item into view assumes there is only a single scrolling component. SpeakList does not support nested scrolling components.
• Components without a speech property will still scroll into view.
• Components without a speech property, but with a positive minimumDwellTime, will have karaoke set for that time.
• Components without a speech property and no minimumDwellTime will not have karaoke set.

The SpeakList command is ignored in fast mode.

align

The alignment of the item on the screen after scrolling and before speech. Alignment is an enumerated value with the following options:

componentId

The ID of the parent component. If omitted, the component issuing the SpeakList command is used.

count

The number of items to speak. The command does not run if the count is less than 1 (no scrolling, no speech). If the count is larger than the number of remaining items in the container, it is trimmed to the maximum number of items that can be spoken from the starting point.

minimumDwellTime

The minimum amount of time in milliseconds that an item will be highlighted (that is, have the karaoke state set to true). This defaults to 0.

start

The 0-based index of the first child item in the parent container to scroll into view and speak. Negative values are measured from the end of the parent container. This example the last three items in a list:

{
  "type": "SpeakList",
  "start": -3,
  "count": 3
}

The following algorithm approximates how the reading is done.

let first = start < 0 ? start + children.length : start;
   let last = Math.min(first + count, children.length – 1);

first = Math.max(0, first);

for (let index = first ; index <= last ; index++) {
  let child = children[index];
  scrollIntoView(child);

  if (child.speech) {
    child.setState("karaoke", true);
    speakChildWithMinimumDwell(child, minimumDwellTime);
    child.setState("karaoke", false);
  }
  else if (minimumDwellTime > 0) {
    child.setState("karaoke", true);
    waitForTimeout(minimumDwellTime);
    child.setState("karaoke", false);
  }
}

Related topics

• Commands Overview
• Media Commands