class in UnityEngine.Accessibility
/
Implemented in:UnityEngine.AccessibilityModule
The hierarchy data model that the screen reader uses to navigate and interact with a Unity application.
For a screen reader to navigate an application, it must receive information like what the accessible elements
are, where they are placed on the screen, what role they have, and how the user can interact with them. This
information needs to be organized in a hierarchy of data structures called the AccessibilityHierarchy.
The accessibility hierarchy operates independently of the UI hierarchy. You can use these APIs with any UI
system and even with non-UI elements, such as elements that are part of your game.
The data structures that form the accessibility hierarchy are called AccessibilityNodes. Each node
represents a visual element that needs to be accessible to the screen reader. A node can have zero or more
AccessibilityNode.children and one AccessibilityNode.parent.
AccessibilityHierarchy.rootNodes are the top-level nodes in the hierarchy, having no parent.
Users can navigate the accessibility hierarchy sequentially by moving the screen reader focus from one node to
another in a depth-first traversal order, so they navigate to a node's children before moving to the node's
siblings. The position of the nodes on the screen (given by their AccessibilityNode.frame) does
not affect navigation order.
To enable the screen reader to navigate an accessibility hierarchy, you must assign the hierarchy to
AssistiveSupport.activeHierarchy to activate it. To manage system resources efficiently, Unity
does not save the active hierarchy while the screen reader is off. You must activate the hierarchy each time the
screen reader is turned on (see AssistiveSupport.screenReaderStatusChanged and
AssistiveSupport.isScreenReaderEnabled).
If you modify the active hierarchy, then you must notify the screen reader by calling
AssistiveSupport.NotificationDispatcher.SendLayoutChanged or
AssistiveSupport.NotificationDispatcher.SendScreenChanged (depending on the scale of the changes).
Modifications in the accessibility hierarchy consist of calls to:
- AccessibilityHierarchy.AddNode
- AccessibilityHierarchy.Clear
- AccessibilityHierarchy.InsertNode
- AccessibilityHierarchy.MoveNode
- AccessibilityHierarchy.RemoveNode
- Modifications to node AccessibilityNode.frame values.
These APIs are currently supported on the following platforms:
- RuntimePlatform.Android - starting with Android 8.0 (API level 26)
- RuntimePlatform.IPhonePlayer
- RuntimePlatform.OSXPlayer
- RuntimePlatform.WindowsPlayer
Additional resources:
| Property | Description |
|---|---|
| rootNodes | The root nodes of the hierarchy. |
| Constructor | Description |
|---|---|
| AccessibilityHierarchy | Initializes and returns an empty AccessibilityHierarchy. |
| Method | Description |
|---|---|
| AddNode | Creates a new AccessibilityNode with the given label and adds it to the hierarchy under the given parent. |
| Clear | Resets the hierarchy to an empty state, removing all nodes and the screen reader focus. |
| ContainsNode | Verifies whether the given node exists in the accessibility hierarchy. |
| GetLowestCommonAncestor | Retrieves the lowest common ancestor of two nodes in the accessibility hierarchy. |
| InsertNode | Creates a new AccessibilityNode with the given label and inserts it at the given index in the hierarchy, under the given parent. |
| MoveNode | Moves the node elsewhere in the accessibility hierarchy. For example, under a different parent or at a different position in the parent's child list. |
| RefreshNodeFrames | Refreshes the AccessibilityNode.frame of all nodes in the accessibility hierarchy. |
| RemoveNode | Removes the node from the accessibility hierarchy and removes or re-parents its descendants. |
| TryGetNode | Tries to retrieve the AccessibilityNode with the given ID in the hierarchy. |
| TryGetNodeAt | Tries to retrieve the AccessibilityNode at the given screen coordinates. |