Using Completer in Dart#

About#

A Completer in Dart is a utility that helps you manage the completion of asynchronous operations. It allows you to create and control a Future that can be completed later with a value or an error. This is useful when you need to handle asynchronous operations in a more flexible way than with just Future constructors or async/await.

Information#

What is a Completer?#

• Definition: A Completer is an object that allows you to manually complete a Future with a value or an error. It provides a way to control the lifecycle of the Future, enabling more complex asynchronous workflows.

• Components:

  • Completer Instance: You create an instance of Completer which has a Future property.
  • Completing the Future: You can complete the Future by calling complete with a value or completeError with an error.

Creating a Completer#

• Initialization: Create a Completer instance to obtain a Future that you can control.

  Example:

  import 'dart:async';
  
  void main() {
    Completer<String> completer = Completer<String>();
    Future<String> future = completer.future;
  
    future.then((value) {
      print('Future completed with: $value');
    }).catchError((error) {
      print('Future completed with error: $error');
    });
  
    // Complete the future with a value
    completer.complete('Hello, Dart!');
  }
  

Overall#

The Completer class in Dart provides a way to manually complete a Future with a value or an error. It is useful for managing asynchronous operations where you need to control when and how the Future is completed. By using Completer, you can integrate asynchronous APIs with Dart’s Future model, handle errors gracefully, and manage complex asynchronous workflows with greater flexibility.