DirectionalFocusTraversalPolicyMixin mixin

A mixin class that provides an implementation for finding a node in a particular direction.

This can be mixed in to other FocusTraversalPolicy implementations that only want to implement new next/previous policies.

Since hysteresis in the navigation order is undesirable, this implementation maintains a stack of previous locations that have been visited on the policyData for the affected FocusScopeNode. If the previous direction was the opposite of the current direction, then the this policy will request focus on the previously focused node. Change to another direction other than the current one or its opposite will clear the stack.

For instance, if the focus moves down, down, down, and then up, up, up, it will follow the same path through the widgets in both directions. However, if it moves down, down, down, left, right, and then up, up, up, it may not follow the same path on the way up as it did on the way down.

See also:

Superclass Constraints
Implemented by




hashCode int
The hash code for this object. [...]
read-only, inherited
runtimeType Type
A representation of the runtime type of the object.
read-only, inherited


changedScope({FocusNode node, FocusScopeNode oldScope }) → void
This is called whenever the given node is reparented into a new scope, so that the policy has a chance to update or invalidate any cached data that it maintains per scope about the node. [...]
findFirstFocusInDirection(FocusNode currentNode, TraversalDirection direction) FocusNode
Returns the node in the given direction that should receive focus if there is no current focus in the scope to which the currentNode belongs. [...]
inDirection(FocusNode currentNode, TraversalDirection direction) bool
Focuses the next widget in the given direction in the FocusScope that contains the currentNode. [...]
@mustCallSuper, override
invalidateScopeData(FocusScopeNode node) → void
Clears the data associated with the given FocusScopeNode for this object. [...]
findFirstFocus(FocusNode currentNode) FocusNode
Returns the node that should receive focus if there is no current focus in the FocusScopeNode that currentNode belongs to. [...]
next(FocusNode currentNode) bool
Focuses the next widget in the focus scope that contains the given currentNode. [...]
noSuchMethod(Invocation invocation) → dynamic
Invoked when a non-existent method or property is accessed. [...]
previous(FocusNode currentNode) bool
Focuses the previous widget in the focus scope that contains the given currentNode. [...]
toString() String
Returns a string representation of this object.


operator ==(dynamic other) bool
The equality operator. [...]