iOS

Developer notes

• A carousel is a list of related content items as a horizontal slideshow
• There are a variety of implementation alternatives for a carousel. At least one of the options in the above success criteria for navigating through the elements/slides must be available
• Slides cannot automatically start rotating through carousel unless there is a pause/stop button
• Consider the number of slides/elements in carousel when choosing implementation. Swiping right through the slides of a very large number of slides to get to the next element past the carousel would not be a good user experience. Custom actions/gestures for navigation through the slides should be considered on large carousels on iOS. Then, if the user wants to bypass all the slides, they would simply swipe right to the next element past the carousel
• Alternate implementation to swiping through carousel: Change the slides with interactive page control dots and dynamically announce all the content in the slide along with page index (without focus on slides, only on the dots)

Name

• Programmatic name of any interactive element describes it’s purpose
• Append “, Carousel” to the programmatic name to announce the role, since the carousel is custom and does not have a native role assigned
• If visible text label exists for an interactive component, the programmatic name should match the visible text label.
  • Note: Setting a programmatic name while a visible text label exists may cause VoiceOver to duplicate the announcement of the name. If this happens, hide the visible text label from VoiceOver recognization.
• UIKit
  • You can programmatically set the visible label with setTitle().
    • The carousel’s title will overwrite the carousel’s accessibilityLabel.
  • If a visible label is not applicable in this case, set the carousel’s accessibilityLabel to the label of your choice.
    • To do this in Interface Builder, set the label using the Identity Inspector
  • To hide labels from VoiceOver programmatically, set the label’s isAccessibilityElement property to false
  • To hide labels from VoiceOver using Interface Builder, uncheck Accessibility Enabled in the Identity Inspector.
• SwiftUI
  • If no visible label, use view modifier accessibilityLabel(_:).
  • If button has icon(s), hide the icon(s) from VoiceOver by using view modifier accessibilityHidden(true).

Role

• Since there is no native carousel component, a custom carousel must be implemented.
• The carousel itself has its own role indicated by appending “, Carousel” to the programmatic name.

• Each item in the carousel has its own independent role or accessibility trait. For example, if the item is interactive, the role will be .button.

• UIKit
  • A common method of implementing a carousel involves using UICollectionView and its corresponding protocols. Each item of the carousel is a UICollectionViewCell.
  • Set the accessibilityTraits of the overall carousel role to .adjustable, and then append “, Carousel” to the programmatic name to notify the user of the role
  • An individual item of the carousel will have its own role that is dependent on whether it is interactive. Assign the role that best fits your use case.
• SwiftUI
  • As there are different ways to implement a carousel, use your best judgment for your use case.
  • Append “, Carousel” to the programmatic name for the overall carousel
  • An individual item of the carousel will have its own role that is dependent on whether it is interactive. Assign the role that best fits your use case.
  • Use view modifier accessibilityAddTraits(:) to add traits.
  • If applicable, use view modifier accessibilityRemoveTraits(:) to remove unwanted traits.

Groupings

• Group visible label with the carousel, if applicable.

• Group the title and any description with each item in the carousel.

• UIKit
  1. Ensure that the child elements of the overarching view you want to group in has their isAccessibilityElement properties set to false.
  2. Set isAccessibilityElement to true for the parent view. Then, adjust accessibilityLabel and accessibilityTraits accordingly.
     • If frame does not exist due to custom button, use accessibilityFrameInContainer to set the custom control’s frame to the parent view’s container or view of your choice.
       • You can also unionize two frames with frame.union (i.e. titleLabel.frame.union(subtitleLabel.frame)).
     • Use shouldGroupAccessibilityElement for a precise order if the native order should be disrupted.
     • Use shouldGroupAccessibilityChildren to indicate whether VoiceOver must group its children views. This allows making unique vocalizations or define a particular reading order for a part of the page.
• SwiftUI
  • Use view modifier accessibilityElement(children: .combine) to merge the child accessibility element’s properties into the new accessibilityElement.

State

• Indicate where the item is in the carousel by announcing the position/index out of the total number of items. (see Announcements below)

• UIKit
  • For disabled: Set isEnabled to false. Announcement for disabled is “Dimmed”.
• SwiftUI
  • For disabled, use view modifier disabled().

Focus

• Use the device’s default focus functionality.
• Consider how focus should be managed between child elements and their parent views.

• External keyboard tab order often follows the screen reader focus, but sometimes this functionality requires additional development to manage focus.

• UIKit
  • If VoiceOver is not reaching a particular element, set the element’s isAccessibilityElement to true
    • Note: You may need to adjust the programmatic name, role, state, and/or value after doing this, as this action may overwrite previously configured accessibility.
  • Use accessibilityViewIsModal to contain the screen reader focus inside the modal.
  • To move screen reader focus to newly revealed content, use UIAccessibility.post(notification:argument:) that takes in .screenChanged and the newly revealed content as the parameter arguments.
  • To NOT move focus, but dynamically announce new content: use UIAccessibility.post(notification:argument:) that takes in .announcement and the announcement text as the parameter arguments.
  • UIAccessibilityContainer protocol: Have a table of elements that defines the reading order of the elements.
• SwiftUI
  • For general focus management that impacts both screen readers and non-screen readers, use the property wrapper @FocusState to assign an identity of a focus state.
    • Use the property wrapper @FocusState in conjunction with the view modifier focused(_:) to assign focus on a view with @FocusState as the source of truth.
    • Use the property wrapper @FocusStatein conjunction with the view modifier focused(_:equals:) to assign focus on a view, when the view is equal to a specific value.
  • If necessary, use property wrapper @AccessibilityFocusState to assign identifiers to specific views to manually shift focus from one view to another as the user interacts with the screen with VoiceOver on.

Custom Gestures

• The expected experience is that when users swipe left or right, they are navigating from one section of the screen to another. When users swipe up or down on the carousel, the user is scrolling through the carousel

• UIKit
  • First, ensure that the accessibility trait of the carousel is .adjustable.
  • Then, you are able to take advantage of the accessibilityIncrement and accessibilityDecrement methods

  override func accessibilityIncrement() {
      // Move forward one item
  
  }
  
  override func accessibilityDecrement() {
      // Move backward one item
  
  }
  

• SwiftUI
  • There are many approaches to applying custom gestures to a component
  • One suggestion is to use .accessibilityAdjustableAction with a switch statement for the direction, and changing the index of the cell depending on whether the direction is .increment or .decrement
    • “Incrementing” should move to the next item
    • “Decrementing” should move to the previous item

    .accessibilityAdjustableAction { direction in
        switch direction {
        case .increment:
            // Go to next page
    
        case .decrement:
            // Go to previous page
    
        }
    }
    

    Announcements

  • “Showing slides x of y” are common announcements to give screen readers context of layout
  • “Custom actions available. Swipe up or down to change slides” – common custom actions announcement

Android

Developer notes

• A carousel is a list of related content items as a horizontal slideshow
• There are a variety of implementation alternatives for a carousel. At least one of the options in the above success criteria for navigating through the elements/slides must be available
• Slides cannot automatically start rotating through carousel unless there is a pause/stop button
• Consider the number of slides/elements in carousel when choosing implementation. Swiping right through the slides of a very large number of slides to get to the next element past the carousel would not be a good user experience.
• The container around the carousel on Android can be an alternative for the user to bypass all the slides. The user can enter the container to navigate through the slides, or swipe to the next element past the container.
  • When navigating to a carousel with the screen reader, it should first focus on the entire carousel container
  • Each carousel may have a different number of items, so the label includes the total amount of items and the current item in focus
  • Then, activating the carousel container focuses on the first carousel item
  • Two finger swipe rt or left navigates through the slides putting focus on the next slide in the order
• Alternate implementation to swiping through carousel: Change the slides with interactive page control dots and dynamically announce all the content in the slide along with page index (without focus on slides, just on the dots)

Name

• Programmatic name of any interactive element describes it’s purpose.

• Each item in the carousel, if interactive, has a name that describes the purpose of the control and matches any visible label/all text and image descriptions within item.

• Android View
  • android:text XML attribute
  • Optional: use contentDescription for a more descriptive name, depending on type of view and for elements without a visible label.
  • contentDescription overrides android:text
  • Use labelFor attribute to associate the visible label to the control
• Jetpack Compose
  • If no visible label, use compose modifier semantics contentDescription.
  • If any icons or images need to be hidden for accessibility talkback, use compose modifier semantics invisibleToUser()

Role

• The native Pager component will handle the built-in accessibility behavior

• Each item in the carousel can have the independent role and accessibility trait. For example, if the item is clickable, the role should be button.

• Android View
  • ViewPager
  • CarouselView
• Jetpack Compose
  • Compose foundation HorizontalPager and VerticalPager

Groupings

• Group visible label with the carousel, if applicable.
• Group the title and any description with each item in the carousel
• If the item in carousel is clickable, use compose modifier clickable which will group the child elements automatically.
• If the item in carousel has multi-actions, then spilt the action out of the group with proper focus order on each actions.
• Android View
  • ViewGroup
  • Set the container object’s android:screenReaderFocusable attribute to true, and each inner object’s android:focusable attribute to false. In doing so, accessibility services can present the inner elements’ contentDescription or names, one after the other, in a single announcement.
• Jetpack Compose
  • Modifier.semantics(mergeDescendants = true) {} for the child elements grouping/merging
  • FocusRequester.createRefs() helps to request focus to inner elements with in the group

State

• Indicate where the item is in the carousel by announcing the position/index out of the total number of items. (see Announcements below)

• Indicate the action state if applicable

• Android View
  • Active: android:enabled=true
  • Disabled: android:enabled=false
  • Announcement: disabled
• Jetpack Compose
  • Active: default state is active and enabled. Use Button(enabled = true) or clickable {enabled = true} to specify explicitly
  • Disabled: Button(enabled = false) or clickable {enabled = false} announces as disabled
  • Alternatively can use modifier = Modifier.semantics { disabled() } to announce as disabled

Focus

• Each slide/element in the carousel should be in the view area when it is being announced
• Consider how focus should be managed between child elements and their parent views.

• External keyboard tab order often follows the screen reader focus, but sometimes this functionality requires additional development to manage focus.

• Android View
  • importantForAccessibility makes the element visible to the Accessibility API
  • android:focusable
  • android=clickable
  • Implement an onClick( ) event handler for keyboard, as well as onTouch( )
  • nextFocusDown
  • nextFocusUp
  • nextFocusRight
  • nextFocusLeft
  • accessibilityTraversalBefore (or after)
  • To move screen reader focus to newly revealed content: Type_View_Focused
  • To NOT move focus, but dynamically announce new content: accessibilityLiveRegion(set to polite or assertive)
  • To hide controls: Important_For_Accessibility_false
  • For a ViewGroup, set screenReaderFocusable=true and each inner object’s attribute to keyboard focus (focusable=false)
• Jetpack Compose
  • Modifier.focusTarget() makes the component focusable
  • Modifier.focusOrder() needs to be used in combination with FocusRequesters to define focus order
  • Modifier.onFocusEvent(), Modifier.onFocusChanged() can be used to observe the changes to focus state
  • FocusRequester allows to request focus to individual elements with in a group of merged descendant views
  • Example: To customize the focus events behaviour
    • step 1: define the focus requester prior. val (first, second) = FocusRequester.createRefs()
    • step 2: update the modifier to set the order. modifier = Modifier.focusOrder(first) { this.down = second }
    • focus order accepts following values: up, down, left, right, previous, next, start, end
    • step 3: use second.requestFocus() to gain focus

Code Example

• Jetpack Compose

// Example of Compose horizontal pager with single page snapping
val state = rememberPagerState { 10 }
HorizontalPager(
    state = state,
    modifier = Modifier.fillMaxSize(),
) { pageIndex ->
    Box(
        modifier = Modifier
            .padding(10.dp)
            .background(Color.Blue)
            .fillMaxWidth()
            .aspectRatio(1f),
        contentAlignment = Alignment.Center
    ) {
        Text(text = pageIndex.toString(), fontSize = 32.sp)
    }
}

Announcements

• “In list” or “Showing slides x of y” are common announcements to give screen readers layout context when landing on carousel container
• “Swipe right with two fingers to change slides” – common navigation announcement