insert method

void insert(int index, E element)

This operation is not supported by an unmodifiable list.

Source

void insert(int index, E element) {
  throw new UnsupportedError("Cannot add to an unmodifiable list");
}

© 2012 the Dart project authors
Licensed under the Creative Commons Attribution-ShareAlike License v4.0.
https://api.dartlang.org/stable/1.24.3/dart-collection/UnmodifiableListView/insert.html