Flutter Course: 14.4 Async and Await Keywords

Flutter is a framework based on the Dart language that helps in easily developing modern mobile applications. For efficient asynchronous processing of applications, the Dart language provides the async and await keywords. In this tutorial, we will cover a wide range of topics starting from the concept of asynchronous programming, how to utilize async and await in Flutter, their use cases, and precautions.

1. Concept of Asynchronous Programming

Asynchronous programming is a way for the processor to perform other tasks without waiting for the completion of a specific task. The asynchronous approach has the advantage of making the user interface (UI) smooth and responsive.

For example, when sending a network request, asynchronous programming is needed to ensure that the application does not freeze while waiting for the request to complete.

2. Asynchronous Programming in Dart

Asynchronous programming in Dart is achieved through Future and Stream. A Future can return a result or trigger an error when a specific task is completed. A Stream is a way to handle the flow of asynchronous data events.

2.1 Future

A Future object represents the result of an asynchronous operation. A Future can have two states:

  • Completed: The operation has been successfully performed and a result is returned.
  • Error: An error occurred during the operation.

A Future object can use the then method to define actions after the asynchronous operation is complete or the catchError method to handle errors.

2.2 Stream

A Stream is an object for handling multiple asynchronous events. For example, you can use a Stream to process data asynchronously in cases like web sockets, user input, and file reading. A Stream publishes events every time data is generated, allowing real-time data reception and processing.

3. async and await Keywords

The async and await keywords help write asynchronous programming in Dart more concisely. You can define an async function and use the await keyword within it to wait for the result of a Future object.

3.1 async Function

You can define an asynchronous function using the async keyword. An async function always returns a Future object, allowing you to handle the results of asynchronous operations.

Future fetchData() async {
    // Data fetching operation
}

3.2 await Keyword

The await keyword can only be used inside async functions, and it pauses and waits until a specific Future object is complete. This process does not block other tasks, so the UI does not freeze.

Future fetchData() async {
    var data = await fetchFromAPI();
    print(data);
}

4. Use Cases

Let’s look at various examples of using async and await.

4.1 Simple Network Request

import 'dart:convert';
import 'package:http/http.dart' as http;

Future fetchData() async {
    final response = await http.get(Uri.parse('https://jsonplaceholder.typicode.com/posts'));
    
    if (response.statusCode == 200) {
        var data = json.decode(response.body);
        print(data);
    } else {
        throw Exception('Failed to load data');
    }
}

4.2 Handling User Input

This is an example of asynchronously processing user input.

Future handleUserInput() async {
    String input = await getUserInput(); // Asynchronously get user input
    print('User input: $input');
}

4.3 Asynchronous Data Stream

This is an example of processing asynchronous data using a Stream.

Stream numberStream() async* {
    for (int i = 1; i <= 5; i++) {
        await Future.delayed(Duration(seconds: 1));
        yield i;
    }
}

void main() async {
    await for (int number in numberStream()) {
        print(number);
    }
}

5. Precautions in Asynchronous Programming

There are a few things to be mindful of when using asynchronous programming.

  • UI Updates: You need to call setState() to update the UI after an asynchronous operation is complete.
  • Error Handling: It is advisable to always use try-catch statements when using await to handle potential errors.
  • Performance Optimization: You can optimize performance by leveraging parallel processing of asynchronous tasks whenever possible.

6. Conclusion

In this tutorial, we explored how to use async and await in Flutter and the basic concepts of asynchronous programming. Asynchronous programming is a very important aspect of modern application development and can help provide a better experience for users. As you continue to work with Dart and Flutter, you will improve your skills in handling asynchronous programming.

Learning is ongoing, and understanding the characteristics of frameworks and languages is even more crucial. By understanding and utilizing the concepts of asynchronous programming, you can significantly enhance the performance and user experience of Flutter applications.

I hope this helps you greatly in your Flutter development journey!