Difference between revisions of "LCL Accessibility"

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Line 212: Line 212:
|AccessibleDescription||QAccessibleWidget::setDescription||AXRoleDescription and AXDescription||?||?||-
|AccessibleDescription||QAccessibleWidget::setDescription||AXRoleDescription, AXDescription, AXTitleUIElement||?||?||-
|AccessibleValue||QAccessibleWidget::setValue||AXTitle, AXValue||Value, Name, State||?||-
|AccessibleValue||QAccessibleWidget::setValue||AXValue||Value, Name, State||?||-

Revision as of 13:30, 21 January 2012

Accessibility means planning and developing applications in a way in which everyone will be able to use them, including blind, persons with low vision, with motion disorders, etc.

LCL Accessibility Introduction

The LCL should automatically provide accessibility for all of its standard controls, or allow the underlying widgetset to provide its own accessibility for the controls utilized directly from the widgetset. LCL users need to provide accessibility only for TCustomControl descendents introduced in the application. LCL developers need to provide accessibility for all TCustomControl descendents in the LCL and also for all non-windowed controls in the LCL (such as TLabel).

The accessibility information provided is a tree of accessible objects which represents the controls hierarchy in the application and which can cover both windowed and non-windowed controls. What the screen reader does exactly with this information is theorically up to him to decide, but of course that it is necessary to test to verify if the most popular screen readers are actually using the information provided in the expected way. The LCL is responsible for making this bridges, since it provides a quite simple accessibility interface and platform APIs, in special the one from Mac OS X, are more complex.

TControl will automatically create an accessible object and place it correctly in the accessible objects tree, so it is not necessary to manually create accessible objects unless a control has sub-items which should be represented individually and are not TControl-descendents. One typical example are the items of the TTreeView control. They are not controls, but can be selected individually and therefore each item should be an accessible object on its own.


 TLazAccessibilityRole = (
   larAnimation, // An object that displays an animation.
   larButton, // A button.
   larCell, // A cell in a table.
   larChart, // An object that displays a graphical representation of data.
   larCheckBox, // An object that can be checked or unchecked, or sometimes in an intermediary state
   larClock, // A clock displaying time.
   larColorPicker, // A control which allows selecting a color.
   larComboBox, // A list of choices that the user can select from.
   larDateField, // A controls which displays and possibly allows to choose a date.
   larGrid, // A grid control which displays cells
   larGroup, // A control which groups others, such as a TGroupBox.
   larIgnore, // Something to be ignored. For example a blank space between other objects.
   larImage, // A graphic or picture or an icon.
   larLabel, // A text label as usually placed near other widgets.
   larListBox, // A list of items, from which the user can select one or more items.
   larListItem, // An item in a list of items.
   larMenuBar, // A main menu bar.
   larMenuItem, // A item in a menu.
   larProgressIndicator, // A control which shows a progress indication.
   larResizeGrip, // A grip that the user can drag to change the size of widgets.
   larScrollBar, // A control to scroll another one
   larSpinner, // A control which allows to increment / decrement a value.
   larTabControl, // A control with tabs, like TPageControl.
   larTextEditorMultiline, // A multi-line text editor (for example: TMemo, SynEdit)
   larTextEditorSingleline, // A single-line text editor (for example: TEdit)
   larTrackBar, // A control which allows to drag a slider.
   larTreeView, // A list of items in a tree structure.
   larTreeItem, // An item in a tree structure.
   larWindow // A top level window.
 // The Child Accessible Objects are designed for non-TControl children
 // of a TCustomControl descendent, for example the items of a TTreeView
 { TLazAccessibleObject }
 TLazAccessibleObject = class
   FHandle: PtrInt;
   FPosition: TPoint;
   FSize: TSize;
   function GetHandle: PtrInt;
   function GetPosition: TPoint;
   function GetSize: TSize;
   procedure SetPosition(AValue: TPoint);
   procedure SetSize(AValue: TSize);
   FChildren: TFPList; // of TLazAccessibleObject
   FAccessibleDescription: TCaption;
   FAccessibleValue: TCaption;
   FAccessibleRole: TLazAccessibilityRole;
   class procedure WSRegisterClass; virtual;//override;
   OwnerControl: TControl;
   Parent: TLazAccessibleObject;
   DataObject: TObject; // Available to be used to connect to an object
   SecondaryHandle: PtrInt; // Available for Widgetsets to use
   constructor Create(AOwner: TControl); virtual;
   destructor Destroy; override;
   procedure SetAccessibleDescription(const ADescription: TCaption);
   procedure SetAccessibleValue(const AValue: TCaption);
   procedure SetAccessibleRole(const ARole: TLazAccessibilityRole);
   function FindOwnerWinControl: TWinControl;
   function AddChildAccessibleObject: TLazAccessibleObject; virtual;
   procedure ClearChildAccessibleObjects;
   procedure RemoveChildAccessibleObject(AObject: TLazAccessibleObject);
   function GetChildAccessibleObject(AIndex: Integer): TLazAccessibleObject;
   function GetChildAccessibleObjectWithDataObject(ADataObject: TObject): TLazAccessibleObject;
   function GetChildAccessibleObjectsCount: Integer;
   function GetSelectedChildAccessibleObject: TLazAccessibleObject; virtual;
   function GetChildAccessibleObjectAtPos(APos: TPoint): TLazAccessibleObject; virtual;
   // Primary information
   property AccessibleDescription: TCaption read FAccessibleDescription write SetAccessibleDescription;
   property AccessibleValue: TCaption read FAccessibleValue write SetAccessibleValue;
   property AccessibleRole: TLazAccessibilityRole read FAccessibleRole write SetAccessibleRole;
   property Position: TPoint read GetPosition write SetPosition;
   property Size: TSize read GetSize write SetSize;
   property Handle: PtrInt read GetHandle write FHandle;
 TControl = class(TLCLComponent)


   // accessibility
   function GetAccessibleObject: TLazAccessibleObject;
   function CreateAccessibleObject: TLazAccessibleObject; virtual;
   function GetSelectedChildAccessibleObject: TLazAccessibleObject; virtual;
   function GetChildAccessibleObjectAtPos(APos: TPoint): TLazAccessibleObject; virtual;
   // standard properties, which should be supported by all descendants
   property AccessibleDescription: TCaption read GetAccessibleDescription write SetAccessibleDescription;
   property AccessibleValue: TCaption read GetAccessibleValue write SetAccessibleValue;
   property AccessibleRole: TLazAccessibilityRole read GetAccessibleRole write SetAccessibleRole;




Obtaining the accessible object associated with a control

Use TControl.GetAccessibleObject: TLazAccessibleObject;

Setting the basic accessible fields for a control

Use TControl.AcessibleDescription, TControl.AccessibleValue, TControl.AccessibleRole. TControl.GetAccessibleObject().AccessibleDescription is the same thing as TControl.AccessibleDescription and they are connected.

Screen Readers

The first step in testing screen reader support is installing one and being able to use it to check what users will see when using your application.

Mac OS X VoiceOver

The screen reader for the vast majority of users in Mac OS X is VoiceOver which comes pre-installed in Mac OS X. To activate it go to Settings->Universal Access and turn VoiceOver on. It couldnt be any simpler. Using it is also mostly easy and intuitive.

Orca for Linux

Orca is currently the most popular screen reader in Linux for both GNOME and KDE. See: http://en.wikipedia.org/wiki/Orca_(assistive_technology)

Accessibility Inspector Tools

Accessibility inspectors can help a lot at checking if the application is giving correct information.

Mac OS X

In /Developer/Applications/Utilities/Accessibility Tools/ there is an Accessibility Inspector which will be very useful when developing in this platform.

Accessibility APIs


Search Google for:

site:developer.apple.com carbon accessibility

The main accessibility code for Carbon is in lcl/interfaces/carbon/carbonprivatecontrol.inc in the function CarbonControl_Accessibility

The events for this handler are:

  • kEventAccessibleGetChildAtPoint
  • kEventAccessibleGetFocusedChild
  • kEventAccessibleGetAllAttributeNames
  • kEventAccessibleGetAllParameterizedAttributeNames
  • kEventAccessibleGetNamedAttribute
  • kEventAccessibleSetNamedAttribute
  • kEventAccessibleIsNamedAttributeSettable
  • kEventAccessibleGetAllActionNames
  • kEventAccessiblePerformNamedAction
  • kEventAccessibleGetNamedActionDescription

For kEventAccessibleGetNamedAttribute the main named attributes are:

  • AXRole
  • AXRoleDescription
  • AXDescription
  • AXHelp
  • AXParent
  • AXChildren
  • AXWindow
  • AXTopLevelUIElement
  • AXEnabled
  • AXSize
  • AXPosition

And besides the ones listed here there are tons more. See which attributes each role should implement here: http://developer.apple.com/library/mac/#documentation/UserExperience/Reference/Accessibility_RoleAttribute_Ref/Role.html#//apple_ref/doc/uid/TP40007870-Roles-AXStaticText

Table explaining the events: http://developer.apple.com/library/mac/#documentation/Accessibility/Reference/AccessibilityCarbonRef/Reference/reference.html

Documentation explaining in details which attributes are required for each Role: http://developer.apple.com/library/mac/#documentation/UserExperience/Reference/Accessibility_RoleAttribute_Ref/Attributes.html


Microsoft Active Accessibility

See: http://en.wikipedia.org/wiki/Microsoft_Active_Accessibility

Also: http://www.stevetrefethen.com/blog/UsingtheMSAAIAccessibleinterfacewithinaDelphiApplication.aspx

AT-SPI for Linux

See: http://en.wikipedia.org/wiki/AT-SPI


See: http://doc.qt.nokia.com/4.3/qaccessiblewidget.html

Also: http://doc.qt.nokia.com/4.3/qaccessible.html#Role-enum

Also: http://doc.qt.nokia.com/qq/qq24-accessibility.html

Concepts mapping

TLazAccessibleObject Qt Mac OS X MSAA AT-SPI Comments
AccessibleRole QAccessible::Role AXRole Role ? -
AccessibleDescription QAccessibleWidget::setDescription AXRoleDescription, AXDescription, AXTitleUIElement ? ? -
AccessibleValue QAccessibleWidget::setValue AXValue Value, Name, State ? -
Position ? AXPosition ? ? -
Size ? AXSize ? ? -
Handle ? AXUIElementRef ? ? -
Parent ? AXParent ? ? -
SecondaryHandle ? ? ? ? -

See Also