1. protected
  2. mustCallSuper
void debugFillDescription(List<String> description)

Accumulates a list of strings describing the object's state. Subclasses should override this to have their information included in toString.

Source 

@protected
@mustCallSuper
void debugFillDescription(List<String> description) {
  if (_current == null)
    description.add('unresolved');
  else
    description.add('$_current');
  description.add('${_listeners.length} listener${_listeners.length == 1 ? "" : "s" }');
}