Android

Developer notes

• Snackbars and Toasts provide lightweight feedback about an operation
• They show a brief non-critical message at the bottom of the screen on mobile
• Snackbar or toast must be dynamically announced by the screen reader without moving focus to it
• Display only one at a time
• A Snackbar or toast can be timed to disappear, since the message is not critical information
• If the Snackbar persists, it should be in the swipe order for the screen reader user and tab order for the keyboard user
• All text in the Snackbar and Toast must be announced by the screen reader
• A Snackbar can contain an interactive element. Please follow the Native Button guidance for the CTA
• Toasts do not contain an interactive element

Focus

• For Jetpack Compose Snackbar, when there is an action available, the default accessibility behavior allows screen reader to dynamically read the message and the action
• Only manage focus when needed. Primarily, let the device manage default focus
• 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 needs focus management

• Initial focus on a screen should land in a logical place (back button, screen title, first text field, first heading)

• Android Views
  • 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: importantForAccessibility=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
    • 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

val snackbarHostState = remember { SnackbarHostState() }
val scope = rememberCoroutineScope()
Scaffold(
    snackbarHost = { SnackbarHost(snackbarHostState) },
    content = { innerPadding ->
        Button(
          modifier = Modifier.padding(innerPadding),
          onClick = {
            // show snackbar as a suspend function
            scope.launch {
                snackbarHostState.showSnackbar("Snackbar Message")
            }
          }) {
              Text(text = "Snackbar")
          }
    }
)