FocusManager class

Manages the focus tree.

The focus tree is a separate, sparser, tree from the widget tree that maintains the hierarchical relationship between focusable widgets in the widget tree.

The focus manager is responsible for tracking which FocusNode has the primary input focus (the primaryFocus), holding the FocusScopeNode that is the root of the focus tree (the rootScope), and what the current highlightMode is. It also distributes key events from KeyEventManager to the nodes in the focus tree.

The singleton FocusManager instance is held by the WidgetsBinding as WidgetsBinding.focusManager, and can be conveniently accessed using the FocusManager.instance static accessor.

To find the FocusNode for a given BuildContext, use Focus.of. To find the FocusScopeNode for a given BuildContext, use FocusScope.of.

If you would like notification whenever the primaryFocus changes, register a listener with addListener. When you no longer want to receive these events, as when your object is about to be disposed, you must unregister with removeListener to avoid memory leaks. Removing listeners is typically done in State.dispose on stateful widgets.

The highlightMode describes how focus highlights should be displayed on components in the UI. The highlightMode changes are notified separately via addHighlightModeListener and removed with removeHighlightModeListener. The highlight mode changes when the user switches from a mouse to a touch interface, or vice versa.

The widgets that are used to manage focus in the widget tree are:

• Focus, a widget that manages a FocusNode in the focus tree so that the focus tree reflects changes in the widget hierarchy.
• FocusScope, a widget that manages a FocusScopeNode in the focus tree, creating a new scope for restricting focus to a set of focus nodes.
• FocusTraversalGroup, a widget that groups together nodes that should be traversed using an order described by a given FocusTraversalPolicy.

See also:

• FocusNode, which is a node in the focus tree that can receive focus.
• FocusScopeNode, which is a node in the focus tree used to collect subtrees into groups and restrict focus to them.
• The primaryFocus global accessor, for convenient access from anywhere to the current focus manager state.