putIfAbsent method

@override V putIfAbsent(K key, V ifAbsent())

Look up the value of key, or add a new entry if it isn't there.

Returns the value associated to key, if there is one. Otherwise calls ifAbsent to get a new value, associates key to that value, and then returns the new value.

Map<String, int> scores = {'Bob': 36};
for (var key in ['Bob', 'Rohan', 'Sophena']) {
  scores.putIfAbsent(key, () => key.length);
}
scores['Bob'];      // 36
scores['Rohan'];    //  5
scores['Sophena'];  //  7

Calling ifAbsent must not add or remove keys from the map.

Implementation

@override
V putIfAbsent(K key, V Function() ifAbsent) {
  final value = super.value.putIfAbsent(key, ifAbsent);
  if (notifyOnChangeMap) {
    notifyListeners();
  }
  return value;
}