Accessibility/Comparisons:ATK To UA: Difference between revisions

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= Comparing some ATK interfaces to UA =
= Comparing some ATK interfaces to UA =
This page attempts to provide an overview of UA, comparing it to some interfaces in ATK. I highgly recommend to [[Mac:Accessibility/UniversalAccess|read the introduction to UA]] before reading this document.
This page attempts to provide an overview of UA, comparing it to some interfaces in ATK. I highly recommend to [[Mac:Accessibility/UniversalAccess|read the introduction to UA]] before reading this document.


Any developer serious in implementing UA support should always read [http://developer.apple.com/documentation/Cocoa/Conceptual/Accessibility/index.html#//apple_ref/doc/uid/10000118i Apple's official accessibility documentation]; this is by no means an end-all be-all document, but can give you an idea about how things work. Feel free to add and edit entries.
Any developer serious in implementing UA support should always read [http://developer.apple.com/documentation/Cocoa/Conceptual/Accessibility/index.html#//apple_ref/doc/uid/10000118i Apple's official accessibility documentation]; this is by no means an end-all be-all document, but can give you an idea about how things work. Feel free to add and edit entries.
Note that this page only is interesting if you're implementing UA support in your application, AT developers use [[Mac:Accessibility/UniversalAccess#AT_APIs.2C_and_client_APIs|other APIs]].


= Interfaces =
= Interfaces =
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; accessibilityActionDescription : returns a human-readable (localized) description of a specified action.
; accessibilityActionDescription : returns a human-readable (localized) description of a specified action.
; accessibilityPerformAction : performs a specified action.
; accessibilityPerformAction : performs a specified action.
There are [[Mac:Accessibility/UniversalAccess#AT_APIs.2C_and_client_APIs|AT APIs]] for getting a localized name for an action (e.g., what the "AXPress" action would be in human-readable english).


== Making a view/widget accessible (AtkComponent) ==
== Making a view/widget accessible (AtkComponent) ==
In UA, every widget has to implement a few methods to be made accessible. Those views that are invisible, and uninteresting to the user should implement the [http://developer.apple.com/documentation/Cocoa/Reference/ApplicationKit/Protocols/NSAccessibility_Protocol/Reference/Reference.html#//apple_ref/occ/instm/NSObject/accessibilityIsIgnored accessibilityIsIgnored] method to return NO (false).
=== Ignored nodes ===
In UA, every widget has to implement a few methods to be made accessible. Those views that are invisible, and uninteresting to the user should implement the [http://developer.apple.com/documentation/Cocoa/Reference/ApplicationKit/Protocols/NSAccessibility_Protocol/Reference/Reference.html#//apple_ref/occ/instm/NSObject/accessibilityIsIgnored accessibilityIsIgnored] method to return NO (false).
 
The ignored objects in the hierarchy are skipped, and the AT will only "see" children, siblings, or parents that are not marked as ignored.


The position and size of a widget is not accessible-specific, so you call the necessary NSView methods to get that information.
=== Hit testing ===
You return the position/size of your widget when the AT asks for the [http://developer.apple.com/documentation/Cocoa/Reference/ApplicationKit/Protocols/NSAccessibility_Protocol/Reference/Reference.html#//apple_ref/doc/c_ref/NSAccessibilitySizeAttribute AXSize] or [http://developer.apple.com/documentation/Cocoa/Reference/ApplicationKit/Protocols/NSAccessibility_Protocol/Reference/Reference.html#//apple_ref/doc/c_ref/NSAccessibilityPositionAttribute AXPosition] attributes.


Hit-testing (getting the accessible object at a given point on the screen) can be done using the [http://developer.apple.com/documentation/Cocoa/Reference/ApplicationKit/Protocols/NSAccessibility_Protocol/Reference/Reference.html#//apple_ref/occ/instm/NSObject/accessibilityHitTest: accessibilityHitTest:] method on any view.
Hit-testing (getting the accessible object at a given point on the screen) is done using the [http://developer.apple.com/documentation/Cocoa/Reference/ApplicationKit/Protocols/NSAccessibility_Protocol/Reference/Reference.html#//apple_ref/occ/instm/NSObject/accessibilityHitTest: accessibilityHitTest:] method, where you want to return the bottom-most widget in your internal hierarchy.


To get the currently focused widget's accessibility object, [http://developer.apple.com/documentation/Cocoa/Reference/ApplicationKit/Protocols/NSAccessibility_Protocol/Reference/Reference.html#//apple_ref/occ/instm/NSObject/accessibilityFocusedUIElement accessibilityFocusedUIElement] is used, which will return the deepest accessible descendant.
=== Focus ===
To get the currently focused widget's accessibility object, [http://developer.apple.com/documentation/Cocoa/Reference/ApplicationKit/Protocols/NSAccessibility_Protocol/Reference/Reference.html#//apple_ref/occ/instm/NSObject/accessibilityFocusedUIElement accessibilityFocusedUIElement] is used, where you need to return the element that is focused.


To set focus, there is the AXFocused attribute that is often settable. To see if a specified attribute is settable, use the [http://developer.apple.com/documentation/Cocoa/Reference/ApplicationKit/Protocols/NSAccessibility_Protocol/Reference/Reference.html#//apple_ref/occ/instm/NSObject/accessibilityIsAttributeSettable: accessibilityIsAttributeSettable:] and then [http://developer.apple.com/documentation/Cocoa/Reference/ApplicationKit/Protocols/NSAccessibility_Protocol/Reference/Reference.html#//apple_ref/occ/instm/NSObject/accessibilitySetValue:forAttribute: accessibilitySetValue:forAttribute:] to set it.
To set focus, there is the AXFocused attribute that is often settable. To see if a specified attribute is settable, use the [http://developer.apple.com/documentation/Cocoa/Reference/ApplicationKit/Protocols/NSAccessibility_Protocol/Reference/Reference.html#//apple_ref/occ/instm/NSObject/accessibilityIsAttributeSettable: accessibilityIsAttributeSettable:] and then [http://developer.apple.com/documentation/Cocoa/Reference/ApplicationKit/Protocols/NSAccessibility_Protocol/Reference/Reference.html#//apple_ref/occ/instm/NSObject/accessibilitySetValue:forAttribute: accessibilitySetValue:forAttribute:] to set it.


To "manually" traverse and inspect the accessibility hierarchy of a view/widget, you get the value of these attributes:
=== Traversing the hierarchy ===
When the AT traverses your hierarchy, it requests the following attributes, that you need to implement in all accessible objects:
; AXChildrenAttribute : will return an array of all accessible children of the widget, skipping any ignored widgets on the way.
; AXChildrenAttribute : will return an array of all accessible children of the widget, skipping any ignored widgets on the way.
; AXParentAttribute : will return the accessible parent of this widget, skipping any ignored widgets on the way.
; AXParentAttribute : will return the accessible parent of this widget, skipping any ignored widgets on the way.
If an object wants to know its order relative to its siblings, it can ask the parent for the AXChildrenAttribute.
=== Values in a widget ===
To get the value of most widgets (barring textviews, and other widgets with very rich content) you simply get the [http://developer.apple.com/documentation/Cocoa/Reference/ApplicationKit/Protocols/NSAccessibility_Protocol/Reference/Reference.html#//apple_ref/doc/c_ref/NSAccessibilityValueAttribute AXValue] attribute.
Minimum and maximum values (for e.g., sliders and progressbars) can be returned from the [http://developer.apple.com/documentation/Cocoa/Reference/ApplicationKit/Protocols/NSAccessibility_Protocol/Reference/Reference.html#//apple_ref/doc/c_ref/NSAccessibilityMaxValueAttribute AXMinValue] and [http://developer.apple.com/documentation/Cocoa/Reference/ApplicationKit/Protocols/NSAccessibility_Protocol/Reference/Reference.html#//apple_ref/doc/c_ref/NSAccessibilityMinValueAttribute AXMaxValue] attributes.
=== Conceptual links ===
There are also [http://developer.apple.com/documentation/Cocoa/Reference/ApplicationKit/Protocols/NSAccessibility_Protocol/Reference/Reference.html#//apple_ref/doc/uid/20000945-DontLinkElementID_16 attributes for linking a label to its widget, the widget to its label, and the AXLinkedUIElement attribute] that can be used to linked elements together than in the interface only are linked visually.


== Traversing the DOM (AtkDocument, AtkHypertext) ==
== Traversing the DOM (AtkDocument, AtkHypertext) ==
'''AtkDocument''' is ATK's way to expose the DOM to client applications. To my knowledge, this does not (yet) exist in UA, as with many advanced features (particularly those web-specific).
'''AtkDocument''' is ATK's way to expose the DOM to client applications. To my knowledge, this does not (yet) exist in UA, as with many advanced features (particularly those web-specific).


'''AtkHypertext''' seems to be ATK's APIs to let a client application easily traverse the links on a page. No such feature exists in OS X, although I don't think it's necessarily impossible to do.
This is one of the areas where it's showing that UA was designed for desktop applications, and not for rich web browsers. Hopefully features features in the future UA will address this kind of gap.


== Text editing (AtkEditableText) ==
== Text editing (AtkEditableText) ==
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* Get the range for a line, or an index, or all visible characters
* Get the range for a line, or an index, or all visible characters
In other words, contrary to ATK, text runs themselves do not contain accessible objects.
In other words, contrary to ATK, text runs themselves do not contain accessible objects.
Textviews can thus be considered to be "opaque". Their contents can't be traversed like in ATK; instead they are queried for specific ranges or points. This makes it harder to make accessible rich-text editing.


== Links (AtkHyperlink) ==
== Links (AtkHyperlink) ==
Hwaara
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