Dart/Flutter - Join List To String with Separator Examples

This tutorial shows you how to join a List to a String with any separator in Dart/Flutter.

Using String join()

Dart's List class has an instance method join() that can be used to join a List of any type to a String.

  String join([String separator = ""])

Below is a simple example in which we are going to join a list of strings into a string. Without passing the separator parameter, the default separator (empty string) will be used. Therefore, the result is the same as concatenating the values without a separator.

  List<String> values = ['dart', 'flutter', 'programming'];
  print(values.join());

Output:

  dartflutterprogramming

If you pass an argument, it will be used as the separator between elements.

  List<String> values = ['dart', 'flutter', 'programming'];
  print(values.join(','));

Output:

  dart,flutter,programming

In case you want to transform the value first, you can create a chain and map the values first before adding join at the end of the chain.

  List<String> values = [' dart', 'flutter ', 'programming'];
  String result = values
      .map((val) => val.trim())
      .join(',');
  print(result);

Output:

  dart,flutter,programming

Join Object

How to handle If the list is a collection of objects, not simple data types (such as string, double, or int? Dart uses toString method of the object's class. Therefore, if you create your own class and you want to join a list of the object into a string, it is necessary to override toString method.

  class Item {
  
    int id;
    String name;
  
    Item({this.id, this.name});
  
    @override
    String toString() {
      return '{id: $id, name: $name}';
    }
  }

  Item item1 = Item(id: 1, name: 'Item One');
  Item item2 = Item(id: 2, name: 'Item Two');
  Item item3 = Item(id: 3, name: 'Item Three');
  List items = [item1, item2, item3];
  print(items.join(','));

Output:

  {id: 1, name: Item One},{id: 2, name: Item Two},{id: 3, name: Item Three}

Without overriding toString, the output will be:

  Instance of 'Item',Instance of 'Item',Instance of 'Item'

That's all about how to convert a List into a String with separator. If you want to perform the reverse thing, you can read our tutorial about how to convert a List with any delimiter to a String.