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Learn Dart: The First Step to Flutter

Futures, async, and await (Single Asynchronous Value)

Explore how to manage single asynchronous values in Dart using Futures, async, and await. Understand how these features make asynchronous code readable and non-blocking, enabling smooth UI performance and efficient background tasks in Flutter development.

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Understanding futures

In Dart, asynchronous operations return a special object called a Future. Think of a Future like a receipt at a busy coffee shop. You place your order, and instead of handing you the coffee immediately, the cashier hands you a receipt.

This receipt represents a potential value (your coffee) that will be available sometime in the future. Because you have the receipt, you can step aside and do other things while the coffee is being brewed without blocking the line.

A Future exists in one of two main states:

  1. Uncompleted: The background task is still running (the coffee is brewing).

  2. Completed: The task is finished. A future can complete successfully with data (you get your coffee), or it can complete with an error (the coffee machine broke).

Let us look at what happens if we try to print a Future before it has completed.

Dart
Future<String> orderCoffee() {
  return Future.delayed(Duration(seconds: 2), () {
    return 'Caramel Macchiato';
  });
}
void main() {
  print('1. Ordering coffee...');
  
  final myReceipt = orderCoffee();
  print('2. Holding: $myReceipt');
}

  • Lines 1—5: We define a function that returns a Future<String>. We use Future.delayed to simulate a two-second brewing process before the string data is ready. ...