Category: Flutter course

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!

Flutter is a powerful open-source UI framework for creating multi-platform applications. In this course, we will take a detailed look at one of Flutter’s important concepts: the Event Loop. The event loop plays a crucial role in asynchronous programming, and it is essential for enhancing UI responsiveness and performance. Understanding asynchronous programming is a vital element in developing Flutter applications.

What is an Event Loop?

An event loop is a mechanism that handles events occurring in the state of a running program. Asynchronous languages like JavaScript and frameworks like Flutter can execute code asynchronously through the event loop rather than in a synchronous, sequential manner. Here, ‘asynchronous’ means that the execution of the code is separate from the main flow, allowing for the processing or execution of tasks while other work is ongoing.

The Need for Asynchronous Programming

Today’s applications have a lot of interaction with users, and tasks such as network requests and file I/O are frequent. If the UI thread has to wait for each task to complete, the application will become slow and unresponsive, causing user discomfort. To prevent this, it is essential to use asynchronous programming and leverage the event loop to handle background tasks.

Flutter’s Event Loop

The event loop in Flutter is managed by the Dart runtime. Since the Dart language follows a single-threaded model, all events are executed on the main thread. This structure is designed to allow smooth interaction between the UI and business logic. The event loop consists of the following key components:

• Event Queue: Holds the events that need to be processed. Various events such as keyboard input, mouse clicks, and network responses are stored and processed in this queue.
• Microtask Queue: A special queue that holds tasks with higher priority. Microtasks are executed before regular tasks. For example, completion handlers for asynchronous tasks like Future instances are stored in this queue.
• Asynchronous Functions: In Dart, you can define asynchronous functions using the async/await keywords. These functions play an important role in the event loop and control the flow of asynchronous tasks.

How the Event Loop and Asynchronous Functions Work

The Flutter event loop operates in the following manner:

1. When the main event loop is running, it first checks the event queue and microtask queue.
2. If the microtask queue is not empty, all microtasks are executed sequentially until they are complete. Microtasks have a higher priority than regular tasks.
3. Once the microtasks are completed, it checks the event queue next to process any pending events.

By doing this, the UI can perform smoothly and responsively, allowing users to interact with the application without delays.

Sample Code Example

The following is a simple code example utilizing asynchronous programming and the event loop in Flutter:

import 'package:flutter/material.dart';

void main() => runApp(MyApp());

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: Scaffold(
        appBar: AppBar(title: Text('Event Loop Example')),
        body: Center(child: MyHomePage()),
      ),
    );
  }
}

class MyHomePage extends StatefulWidget {
  @override
  _MyHomePageState createState() => _MyHomePageState();
}

class _MyHomePageState extends State {
  String _data = "The result will appear here.";

  Future _fetchData() async {
    setState(() {
      _data = "Fetching data...";
    });

    // Perform asynchronous task
    await Future.delayed(Duration(seconds: 2));

    // Data fetching complete
    setState(() {
      _data = "Data fetched successfully!";
    });
  }

  @override
  Widget build(BuildContext context) {
    return Column(
      mainAxisAlignment: MainAxisAlignment.center,
      children: [
        Text(_data),
        SizedBox(height: 20),
        ElevatedButton(
          onPressed: _fetchData,
          child: Text('Fetch Data'),
        ),
      ],
    );
  }
}

In this example, clicking the button simulates the process of fetching data asynchronously. When the user clicks the button, the UI shows the message ‘Fetching data…’, and once the asynchronous task is completed, the result is updated. This code demonstrates how the event loop and asynchronous programming work.

Conclusion

In this course, we explored Flutter’s event loop and asynchronous programming. Asynchronous processing is crucial in modern applications and is one of the powerful features of the Flutter framework. By understanding and utilizing the event loop, you can enhance user experience and develop applications with better performance.

In the next course, we will delve into more advanced concepts of asynchronous programming and various examples. I encourage you to continue learning, and feel free to leave any questions or comments!

Author: [Your Name]

Date: [Today’s Date]

The Importance of Asynchronous Programming

Asynchronous programming is an essential element in modern application development. In particular, asynchronous tasks are very important for improving user experience (UX) and increasing responsiveness. The asynchronous approach allows multiple tasks to be performed simultaneously, enabling the execution of other tasks while waiting for one task to complete. This enables users to use applications that are faster and smoother.

Asynchronous Programming in Flutter

Asynchronous programming in Flutter is primarily implemented through the Future and async/await keywords. Flutter is written in the Dart programming language and offers various features to facilitate asynchronous programming easily. Now, let’s take a look at how to use asynchronous functions in Flutter.

Future and Asynchronous Functions

Future is a class that represents the result of an asynchronous operation. A Future object represents a task that will complete in the future and is returned from an asynchronous function. An asynchronous function is defined with the async keyword, and it uses the await keyword internally to wait for the Future to complete.

Asynchronous Function Example

Future fetchData() async {
    await Future.delayed(Duration(seconds: 2));
    return "Data loading completed!";
}
            

The example above is an asynchronous function that returns the string “Data loading completed!” after waiting for 2 seconds.

Usage of await

The await keyword causes execution to wait until the Future is completed, enabling the sequential execution of asynchronous code. For example, here’s how to call the fetchData function above.

await Example

void main() async {
    print("Loading data...");
    String result = await fetchData();
    print(result);
}
            

The main function is also defined as async, and it uses await to wait for the result of the fetchData function. This allows the message “Loading data…” to be printed immediately, and after 2 seconds, “Data loading completed!” is printed.

Error Handling in Asynchronous Tasks

Error handling in asynchronous tasks is an important aspect. You can handle exceptions occurring in asynchronous functions using a try-catch block.

Error Handling Example

Future fetchWithError() async {
    throw Exception("An error occurred!");
}

void main() async {
    try {
        String result = await fetchWithError();
        print(result);
    } catch (e) {
        print("Error: ${e.toString()}");
    }
}
            

In the example above, the fetchWithError function throws an exception. The main function wraps the call to that function in a try-catch block to handle the error.

Various Methods to Manage Future

To manage asynchronous processing more effectively in Flutter, there are methods provided to execute multiple Futures simultaneously. Using the Future.wait method makes it possible to wait for multiple Futures at the same time.

Future.wait Example

Future fetchAllData() async {
    var first = fetchData();
    var second = fetchWithError();
    var results = await Future.wait([first, second]);

    print(results);
}

void main() async {
    try {
        await fetchAllData();
    } catch (e) {
        print("Error: ${e.toString()}");
    }
}
            

The fetchAllData function executes two Futures simultaneously and waits for the results. If the second Future throws an error, the catch block handles the error.

Utilizing Streams

A stream is used to handle the continuous flow of asynchronous data. It is useful in scenarios where data is generated continuously, such as websocket connections, file reading, or database queries. Streams handle a series of events asynchronously.

Stream Example

Stream numberStream() async* {
    for (int i = 0; i < 5; i++) {
        await Future.delayed(Duration(seconds: 1));
        yield i;
    }
}

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

The numberStream function creates a stream and outputs a number every second. The main function uses the await for keyword to access the data from the stream.

Best Practices in Asynchronous Programming

When engaging in asynchronous programming, it is important to follow several best practices:

• Error Handling: Don’t forget to handle exceptions in asynchronous functions.
• Combining Futures: Use Future.wait and Future.any to efficiently handle multiple tasks.
• Using Streams: Consider streams when continuous data processing is needed.

Hello! In this post, we will delve deeply into one of the important concepts in Flutter development, Future. Future is a concept that is useful in asynchronous programming, allowing you to perform other tasks while waiting for the response after requesting data. In this article, we will explain the concept of Future, how to use it, examples, and how it can be utilized in practice.

1. What is Asynchronous Programming?

Asynchronous programming is a programming approach that enables a program to process multiple tasks simultaneously. This is especially useful when performing time-consuming tasks such as network requests or file input/output. In traditional approaches, each task is executed sequentially, and the next task cannot begin until the current one is completed. However, using asynchronous programming allows for other tasks to be performed while waiting for the result of the request, maintaining an efficient program flow.

2. Definition of Future

Future is an object provided by DART for asynchronous programming, representing a promise of the result of a specific operation. Future is generally used to indicate the result of asynchronous tasks such as network requests, file operations, or time delays. A Future can have two states:

• Uncompleted: The operation has not yet been completed.
• Completed: The result has been successfully returned or an error has occurred.

3. How to Use Future

Using Future is very simple. You can handle asynchronous tasks more intuitively using the async and await keywords.

3.1. Creating a Future

A Future can immediately return a value or throw an error using the Future.value() or Future.error() methods. Here is a simple example of creating a Future:

void main() {
    Future futureValue = Future.value("Hello, Future!");
    futureValue.then((value) {
        print(value); // Hello, Future!
    });
}

3.2. Using Future in Asynchronous Methods

Asynchronous methods return a Future, so you need to add the async keyword to the method. For example, an asynchronous method to fetch data from an API looks like this:

Future fetchData() async {
    await Future.delayed(Duration(seconds: 2));
    return "Data from server";
}

4. Checking the State of a Future

If you want to check the state of a Future, you can use the isCompleted, isCompleted, and isError properties. Here’s an actual usage example:

void main() async {
    Future futureValue = fetchData();
    
    futureValue.then((value) {
        print("Received: $value");
    }).catchError((error) {
        print("Error occurred: $error");
    });
    
    print("Future is completed: ${futureValue.isCompleted}");
}

5. Difference Between Future and Callback

In the past, callbacks were used for asynchronous programming. A callback is a function that is called after a specific operation is completed. However, this could lead to a problem known as callback hell, which often reduces readability. In contrast, using Future makes the code much cleaner and easier to read.

5.1. Callback Example

void fetchDataWithCallback(Function callback) {
    Future.delayed(Duration(seconds: 2), () {
        callback("Data from server");
    });
}

5.2. Future Example

void main() async {
    String data = await fetchData();
    print(data);
}

6. Applications of Future

There are various ways to use Future. Here, we will explain the utilization of Future through some practical examples.

6.1. Calling REST API

In many cases, a situation arises where data needs to be fetched asynchronously from a REST API. This can be implemented using Future. Here is an example of requesting data using the HTTP package:

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

Future fetchPost() async {
    final response = await http.get(Uri.parse('https://jsonplaceholder.typicode.com/posts/1'));

    if (response.statusCode == 200) {
        final post = json.decode(response.body);
        print('Title: ${post['title']}');
    } else {
        throw Exception('Failed to load post');
    }
}

void main() {
    fetchPost();
}

6.2. Reading Files

In Flutter, Future is also used to read data from the file system. Here is an example of reading data from a local file:

import 'dart:io';

Future readFile(String path) async {
    final file = File(path);
    String contents = await file.readAsString();
    return contents;
}

void main() async {
    String data = await readFile('example.txt');
    print(data);
}

7. Future and Stream

While Future returns a single value result, Stream can return multiple values through asynchronous operations. Understanding the structure of Future and Stream allows you to select the appropriate tool for effective asynchronous programming.

7.1. Stream Example

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

void main() async {
    await for (var count in countStream()) {
        print(count);
    }
}

8. Advantages and Disadvantages of Future

Future effectively supports asynchronous programming, but it is important to understand its advantages and disadvantages.

8.1. Advantages

• Asynchronous tasks can be easily managed.
• The code is more concise and has higher readability.
• It provides catchError for error handling, helping to write stable code.

8.2. Disadvantages

• It is important to manage the state properly during asynchronous tasks.
• Complex asynchronous tasks can make code maintenance difficult.

9. Conclusion

Future is an important element for implementing asynchronous programming in Flutter. I hope this post has helped you understand the concept of Future, how to use it, and various examples. Try to utilize Future to create efficient and responsive applications through asynchronous programming!

10. References

• Dart – Async/Await Codelab
• Flutter – Networking Cookbook