Dart：.toList() 和转换为 List 有什么区别

Question

Out of curiosity and after some research I did not find the same case as mine,

What is the difference between using the method .toList() and casting as List and when should each be used?

Kindly, consider providing an example.

Answer 1

toList() is a method called on multiple types of objects and will gather all data from a data stream (or existing List ) and create a new List object containing the data.

as List is a way to tell a given object (often dynamic ) is in fact a List object on runtime. This is used if we cannot determined the type on compile type (eg if parsing JSON).

Example

We decodes some JSON and tell Dart that we can guarantee that the type on runtime will be List by using as List .

import 'dart:convert';

void main() {
  final list = json.decode('[1, 2, 3]') as List;
  print(list); // [1, 2, 3]

  final newList = list.cast<int>().map((e) => e * 2).toList();
  print(newList); // [2, 4, 6]
}

We then use .map to double each value and want to convert this into a new list by usin toList() .