2. Agenda Introduction Motivation for Accessibility Flex Accessibility API Building Custom accessible Components Best practices Testing Final word
3. Introduction Consultant for Adobe Professional Services Specialized in developing Rich Internet Applications Developing with Flex for 3 year Worked on a public facing RIA for a government organization Took interest in accessibility
4. Motivation for Accessibility Morale arguments Accessibility is the right thing to do 12.8 percent of adults (21-64) are disabled in some way Ensure equal access for individuals with disabilities Improves the application’s design by thinking upfront of accessibility constraints Also benefits the mainstream audience it is our duty to design and develop accessible websites as part of our work
39. Do not design content in a way that is known to cause seizures
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41. About Accessibility in Flash Introduced with Flash 6 Previously limited to Flash and Flex but not supported in AIR Air 2 now supports Accessibility (built in Flex/Flash) Detailed documentation and Language Reference available Support for assistive technology through Microsoft Active Accessibility (MSAA) API
42. How MSAA works provides a descriptive and standardized way for applications and screen readers to communicate. Middleware architecture that conveys an object model of an application When Internet Explorer or Firefox loads a new page, it sends an event notification to the MSAA system Screen Readers are essentially MSAA clients listening for events
43. Accessible object model in Flash Player The Flash Player's accessible object tree consists of a single top-levelcontainer Contains a flat collection of the following types: Text Input TextField Buttons Simple Movie Clip Scripted Movie Clip
44. Enabling Accessibility for your Flex applications In Flash Builder 4 Select “Generate Accessible SWF file” in the Project properties dialog Modfifies the compiler node : <compiler additionalCompilerArguments="-locale en_US" generateAccessible="true"> in the .actionScriptProperties file This is now selected by default in Flash Builder 4 At Runtime Append accessible=true to the URL http://www.mydomain.com/index.html?accessible=true Using the command line compiler Use the Accessible option with MXMLC mxlmc –accessible MyApplication.mxml
46. Flex Accessible components and containers Adobe built support for accessibility into Flex MX components and containers Accessible components : 28 for Halo - 19 for Spark ButtonBar DropDownList NumericStepper RichEditableText Spinner TabBar ToggleButton VideoPlayer Accordion AdvancedDataGrid Alert Button CheckBox ColorPicker ComboBox DataGrid DateChooser DateField Form Image Label LinkButton List Menu MenuBar Panel RadioButton RadioButtonGroup Slider TabNavigator Text TextArea TextInput TitleWindow ToolTipManager Tree
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48. ForceSimple: If true, causes Flash Player to exclude child objects within this display object from the accessible presentation.
50. Silent: If true, excludes this display object from accessible presentation.
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52. Accessibility API Instanciating the flash.accessiblity.AccessibilityProperties class In MXML <?xml version="1.0" encoding="utf-8"?> <s:Applicationxmlns:fx="http://ns.adobe.com/mxml/2009" xmlns:s="library://ns.adobe.com/flex/spark" xmlns:mx="library://ns.adobe.com/flex/mx"> <s:TextArea id="accessibleTxt" accessibilityName="Spark Accessible Text" accessibilityEnabled="true" accessibilityDescription="A short description" /> </s:Application>
53. Accessibility API The flash.accessibility.Accessibility class provides the following methods and properties: active : Indicates whether a screen reader is currently active and the player is communicating with it. updateProperties():Tells Flash Player to apply any accessibility changes made by using the DisplayObject.accessibilityProperties property. sendEvent: Sends an event to the Microsoft Active Accessibility API. What happens when your OS doesn’t have an active screen reader? Calling updateProperties() will throw an IllegalOperatorErrorexception Use flash.system.Capabilities.hasAccessibilityto detected if the system supports Accessibility And the active property to prevent a call to updateProperties() privatefunctionupdateProperties():void { if (Accessibility.active) { Accessibility.updateProperties(); } }
54. The flash.accessibility.AccessibilityImplementation class Flash provides the flash.accessibility.AccessibilityImplementation class for exposing accessible components subset of the IAccessible interface, adapted slightly for ease of use. The Flash Player IAccessible interfacepasses most calls from MSAA to thesubclass instance for that component Flex components with Accessibility will be treated as scripted movie clips In Flex, this class is extended by mx.accessibility.AccImpl
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56. Building Custom Accessible Components Developers need to be able to provide their own accessibility implementations for custom component You create a new accessibility implementation by extending mx.accessibility.AccImpl for each new component Consider two primary forms of guidance: MSAA documentation has guidelines for objects based on the component type Look at a similar component in an HTML page Make sure you implement keyboard navigation and focus management Go for the easy path and extend accessible components if possible
57. Building Custom Accessible Components Let’s start with an example : Contextual help component You will need to create your implementation class by extending AccImpl The AccConst class provides all the MSSA constants you need. You will have to override some of the methods from the IAccessible interface
58. Building Custom Accessible Components Let’s first create our visual component – the HelpButton class Defining a custom accessibility implementation for a component requires changes the component class file First thing to do – add the AccessibilityClassmetatada tag to let the compiler know which AccessibilityImplementation to use [AccessibilityClass(implementation=”component.HelpButtonAccImpl")] Add a placeholder for the mix-in function mx_internal static var createAccessibilityImplementation:Function; This createAccessibilityImplementation() method will be assigned by the PopUpButtonAccImpl accessibility implementation class we'll create Override the UIComponent.initializeAccessibility() method with the following to initialize the AccessibilityImplementation for a given component instance at runtime. overrideprotectedfunctioninitializeAccessibility():void { if (HelpButton.createAccessibilityImplementation != null) { HelpButton.createAccessibilityImplementation( this ); } }
59. Creating the accessibility implementation Creating the HelpButtonAccImpl which is a subclass of mx.accessibility.AccImpl Constructor We set the appropriate role for the component based on the MSAA constants publicfunctionHelpButtonAccImpl(master:UIComponent) { super( master ); role = AccConst.ROLE_SYSTEM_PUSHBUTTON; }
60. Creating the accessibility implementation Initializing Accessibility for the host component Initializes the creatAccessibilityImplementation property we declared on the host component Creating a new acessibiliyImplementation for each instances of the host component mx_internalstaticfunctioncreateAccessibilityImplementation ( component:UIComponent):void { component.accessibilityImplementation = new HelpButtonAccImpl(component); } publicstaticfunctionenableAccessibility():void { HelpButton.createAccessibilityImplementation = createAccessibilityImplementation; }
61. Creating the accessibility implementation Managing events that will an assistive technology will need to react to Overriding the eventToHandle methods Overriding the EventHandler method to manage these events overrideprotectedfunctiongeteventsToHandle():Array { returnsuper.eventsToHandle.concat([ Event.Change]); } overrideprotectedfunctioneventHandler(event:Event):void { super.eventHandler( event ); switch (event.type) { caseEvent.CHANGE: Accessibility.sendEvent(master, 0, AccConst.EVENT_OBJECT_STATECHANGE); Accessibility.sendEvent(master, 0, AccConst.EVENT_OBJECT_NAMECHANGE); Accessibility.sendEvent(master, 0, AccConst.EVENT_OBJECT_SHOW); Accessibility.sendEvent(master, 0, AccConst.EVENT_OBJECT_FOCUS); Accessibility.updateProperties(); break; } }
62. Creating the accessibility implementation We now need to override methods from the IAccessible interface Overriding the EventHandler method to manage these events overrideprotectedfunctiongetName(childID:uint):String { varlabel:String = helpButton.label; label = ( label != null && label != "" ) ? label : ""; if( helpButton.selected ) { label = label + ". " + helpButton.helpText; } return label; } overridepublicfunctionget_accName(childID:uint):String { varaccName:String = AccImpl.getFormName(master); accName += getName(childID) + getStatusName(); return (accName != null && accName != "") ? accName : null; }
63. Creating the accessibility implementation We now need to override methods from the IAccessible interface overridepublicfunctionget_accDefaultAction(childID:uint):String { return"Press"; } */ overridepublicfunctionget_accState(childID:uint):uint { varaccState:uint = getState(childID); if (HelpButton(master).selected) accState |= AccConst.STATE_SYSTEM_PRESSED; returnaccState; }
65. Best Practices – Reading order Reading order must match the content of the application Default order is Left-Right/Top-Bottom Possible to override but not straightforward : Tab order is flat Doesn’t provide hierarchy If overridden the tab index must be specified to ALL component in the application Allocate slots for each part of your application.
66. Best Practices – Reading order Controlling the reading order in MXML <mx:Form label="login"> <mx:FormItem label="Username"> <mx:TextInputtabIndex="1"/> </mx:FormItem> <mx:FormItemlabel="Password"> <mx:TextInputtabIndex="2"/> </mx:FormItem> <mx:HBox> <mx:Buttonlabel="Reset" tabIndex="3"/> <mx:Buttonlabel="Login" tabIndex="4"/> </mx:HBox> </mx:Form>
67. Best Practices – Global navigation Extremely different from an HTML Page What happens when you navigate ( Changing state or switching content )? By default : nothing! Example : Login screen to dashboard screen Notify the user that a change occurred Explain briefly the new content and the purpose of the screen Set the focus on a relevant component Consider non-mouse driven navigation Everything should be accessible using the keyboard Make sure your navigation components have simple and explicit names Provide auto-scroll when focusing a component
68. Best Practices – Pop Ups What happens by default : again, nothing Correct behavior : Read the title followed by the content of the pop up Set the focus on the default button ( e.g. cancel or ok) Disable the background : the rest of the application is hidden to the screen reader Use a default key to close pop ups (commonly the ESC key)
69. Best Practices - Forms Use Form and FormItem for user input Provide out of the box accessibility features Mandatory Field Validation Set focus on the first input field when entering a form Make sure the user can enter “Form mode” with his screen reader What happens when the validation fails? Focus on the first error Explicitly warn the user that the form is invalid If possible specify the number of errors
70. Best Practices – Adjustable Interface / High contrast Provide resizable text Screen magnification A High constrast version Alternative css Save user preferences
72. Best Practices – Context ad relationship Provide context and relationship : Applications that assume comprehension of visual relationships require extra attention ( i.e hierarchical data) Explicitly add context to links/buttons whenever possible (e.g. :Edit --> Edit your profile) Otherwise use tooltips or description to give more information.
73. Best Practices – visual content Consider users with visual acuity limitations : Don’t rely on colors/images to convey information Provide caption to any images Disable animations Provide instructions: Non-obvious functionality needs to be revealed for users
75. Testing Accessibility MSAA Inspector Tools: Quick tool for identifying role and state info Much faster to test a component Screen reader : Jaws Navigation (test with your keyboard ) : Tabbing through controls is a good start Make sure to shift+tab backwards Try to turn off your monitor and use the application Perform user testing
76. Final word Accessibility is not an easy task Allocate enough time on the project Keep accessibility in mind during all phases ( starting with the design phase) Involve users as soon as possible : Regular users of assistive technologies will provide the most accurate information An accessible application is not necessarily usable – allow time for user testing User expectations are a possible issue Don’t put accessibility on a TODO at the end of the project
The methods of the flash.accessibility.AccessibilityImplementation class are a subset of the IAccessible interface, adapted slightly for ease of use.It class provides a set of methods that allow a component developer to make information about system roles, object based events, and states available to assistive technology. The Flash Player IAccessible interface for a scripted movie clip simply passes most calls from MSAA through to the flash.accessibility.AccessibilityImplementation subclass instance for that component.For example, when a screen reader needs to determine the default action of a mx.controls.Button component instance on the Stage in Flash Player, it calls the IAccessible method get_accDefaultAction() on the IAccessible interface exposed by the Flash Player for that component instance. The request is passed through to the get_accDefaultAction() method of the mx.accessibility.ButtonAccImpl accessibility implementation class instance, which returns the appropriate default action String for a button control, which is “Press.”
