How do I add a value at a specific index to an empty list in dart?

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  List<String> currentList =new List<String>(); 

void initState() {
    super.initState();
    currentList=[];
  }

Future<Null> savePreferences(option,questionIndex) async {
    SharedPreferences prefs = await SharedPreferences.getInstance();
    currentList.insert(questionIndex, option);
  }

So basically what I am trying to do is save an option for a question at the specified index (I checked and the index is returned properly) in shared preferences. When it runs and I press the option, it returns to me the following error:

E/flutter ( 6354): [ERROR:flutter/lib/ui/ui_dart_state.cc(166)] Unhandled Exception: RangeError (index): Invalid value: Valid alue range is empty: 0

The reason I am using the insert method and not the add method is because I want to essentially replace the value that is already stored at the index in the case that the user wants to overwrite their previous answer. Can someone help? Thanks

dart flutter sharedpreferences
1 Answers

If you want something that acts like a sparse array, you can use a Map instead. If you want to be able to iterate over the items in order by numeric index (instead of by insertion order), you could use a SplayTreeMap.

For example:

import 'dart:collection';

void main() {
  final sparseList = SplayTreeMap<int, String>();
  sparseList[12] = 'world!';
  sparseList[3] = 'Hi';
  sparseList[3] = 'Hello';
  for (var entry in sparseList.entries) {
    print('${entry.key}: ${entry.value}');
  }
}

prints:

3: Hello
12: world!
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