addHighlightModeListener method Null safety

void addHighlightModeListener(
  1. ValueChanged<FocusHighlightMode> listener
)

Register a closure to be called when the FocusManager notifies its listeners that the value of highlightMode has changed.

Implementation

void addHighlightModeListener(ValueChanged<FocusHighlightMode> listener) => _listeners.add(listener);