docs » hs.axuielement.observer

This submodule allows you to create observers for accessibility elements and be notified when they trigger notifications. Not all notifications are supported by all elements and not all elements support notifications, so some trial and error will be necessary, but for compliant applications, this can allow your code to be notified when an application's user interface changes in some way.

API Overview

API Documentation

Constants

notifications
Signature hs.axuielement.observer.notifications[]
Type Constant
Description

A table of common accessibility object notification names, provided for reference.

Notes:

  • Notifications are application dependent and can be any string that the application developers choose; this list provides the suggested notification names found within the macOS Framework headers, but the list is not exhaustive nor is an application or element required to provide them.

Constructors

new
Signature hs.axuielement.observer.new(pid) -> observerObject
Type Constructor
Description

Creates a new observer object for the application with the specified process ID.

Parameters:

  • pid - the process ID of the application.

Returns:

  • a new observerObject; generates an error if the pid does not exist or if the object cannot be created.

Notes:

  • If you already have the hs.application object for an application, you can get its process ID with hs.application:pid()
  • If you already have an hs.axuielement from the application you wish to observe (it doesn't have to be the application axuielement object, just one belonging to the application), you can get the process ID with hs.axuielement:pid().

Methods

addWatcher
Signature hs.axuielement.observer:addWatcher(element, notification) -> observerObject
Type Method
Description

Registers the specified notification for the specified accesibility element with the observer.

Parameters:

  • element - the hs.axuielement representing an accessibility element of the application the observer was created for.
  • notification - a string specifying the notification.

Returns:

  • the observerObject; generates an error if watcher cannot be registered

Notes:

  • multiple notifications for the same accessibility element can be registered by invoking this method multiple times with the same element but different notification strings.
  • if the specified element and notification string are already registered, this method does nothing.
  • the notification string is application dependent and can be any string that the application developers choose; some common ones are found in hs.axuielement.observer.notifications, but the list is not exhaustive nor is an application or element required to provide them.
callback
Signature hs.axuielement.observer:callback([fn | nil]) -> observerObject | fn | nil
Type Method
Description

Get or set the callback for the observer.

Parameters:

  • fn - a function, or an explicit nil to remove, specifying the callback to the observer will invoke when the assigned elements generate notifications.

Returns:

  • If an argument is provided, the observerObject; otherwise the current value.

Notes:

  • the callback should expect 4 arguments and return none. The arguments passed to the callback will be as follows:
    • the observerObject itself
    • the hs.axuielement object for the accessibility element which generated the notification
    • a string specifying the specific notification which was received
    • a table containing key-value pairs with more information about the notification, if the element and notification type provide it. Commonly this will be an empty table indicating that no additional detail was provided.
isRunning
Signature hs.axuielement.observer:isRunning() -> boolean
Type Method
Description

Returns true or false indicating whether the observer is currently watching for notifications and generating callbacks.

Parameters:

  • None

Returns:

  • a boolean value indicating whether or not the observer is currently active.
removeWatcher
Signature hs.axuielement.observer:removeWatcher(element, notification) -> observerObject
Type Method
Description

Unregisters the specified notification for the specified accessibility element from the observer.

Parameters:

  • element - the hs.axuielement representing an accessibility element of the application the observer was created for.
  • notification - a string specifying the notification.

Returns:

  • the observerObject; generates an error if watcher cannot be unregistered

Notes:

  • if the specified element and notification string are not currently registered with the observer, this method does nothing.
start
Signature hs.axuielement.observer:start() -> observerObject
Type Method
Description

Start observing the application and trigger callbacks for the elements and notifications assigned.

Parameters:

  • None

Returns:

  • the observerObject

Notes:

  • This method does nothing if the observer is already running
stop
Signature hs.axuielement.observer:stop() -> observerObject
Type Method
Description

Stop observing the application; no further callbacks will be generated.

Parameters:

  • None

Returns:

  • the observerObject

Notes:

  • This method does nothing if the observer is not currently running
watching
Signature hs.axuielement.observer:watching([element]) -> table
Type Method
Description

Returns a table of the notifications currently registered with the observer.

Parameters:

  • element - an optional hs.axuielement to return a list of registered notifications for.

Returns:

  • a table containing the currently registered notifications

Notes:

  • If an element is specified, then the table returned will contain a list of strings specifying the specific notifications that the observer is watching that element for.
  • If no argument is specified, then the table will contain key-value pairs in which each key will be an hs.axuielement that is being observed and the corresponding value will be a table containing a list of strings specifying the specific notifications that the observer is watching for from from that element.