addPropertyChangedListener method Null safety

void addPropertyChangedListener(
  1. DateRangePickerValueChangedCallback listener
)

Calls the listener every time the controller's property changed.

Listeners can be removed with removePropertyChangedListener.

Implementation

void addPropertyChangedListener(
    DateRangePickerValueChangedCallback listener) {
  _listeners ??= <DateRangePickerValueChangedCallback>[];
  _listeners?.add(listener);
}