Flutter; replace item in list

You can also use replaceRange for this:

void main() {
  var list = ['Me', 'You', 'Them'];
  print(list); // [Me, You, Them]
  var selected = 'You'; // user input A (find)
  var newValue = 'Yours'; // user input B (replace)
  
  // find the item you want to replace, in this case, it's the value of `selected`.
  var index = list.indexOf(selected);
  
  // if replacing only one item, the end index should always be `startIndex` +1.
  // `replaceRange` only accepts iterable(list) so `newValue` is inside the array.
  list.replaceRange(index, index + 1, [newValue]);
  
  print(list); // [Me, Yours, Them]
}

for (int i = 0; i < LIST.length; i++){
    if (LIST[i] == USERINPUT1){
        LIST[i] = USERINPUT2;
    }
}

Basically iterate through the list in the app to check if the input is equal to the user's input.

OR

index = LIST.indexOf(USERINPUT1);

if (index != -1){
    LIST[index] = USERINPUT2;
}

This only works for the first occurrence though.

Here is how I would do it:

void main() {
  String inputString = 'myInput'; // User input to replace inside the list
  List<String> list = ['1', inputString, '3', '4', '5', inputString, '7']; // List of items
  List<String> filteredList = list.where((e) => e == inputString).toList();
  for (final e in filteredList) {
    final index = list.indexOf(e);
    list.removeAt(index);
    list.insert(index, 'newInput'); // Replacing inputString by 'newInput'
  }
}

Basically what I'm doing is creating a sublist filteredList containing only the occurrence of the user input. Then I iterate over my filteredList, before removing the item from list I'm keeping its index to insert my new element at the correct position.

Try the code on DartPad

Replace first occurrence for primitive types

final l = [1,2,3,4];
l[l.indexOf(2)] = 5;
print(l); // [1,5,3,4]

I chose to create an extension that determines where the item is in the list, if at all,

• and if in the list will
  • remove the existing value and
  • insert the new value in the same place,
• otherwise it will add the entry in.

{

extension ListExtensions on List {

  List replaceOrAdd(dynamic obj) {
    var index = indexOf(obj);
    if (index >= 0) {
      removeAt(index);
      insert(index, obj);
    } else {
      add(obj);
    }
    return this;
  }
}