Category: Flutter course

Flutter is an open-source UI software development kit (SDK) developed by Google, used to build high-performance UIs for mobile, web, and desktop applications. In this course, we will explain one of Flutter’s core concepts, ‘state management’, and take a closer look at Stateful widgets. The course includes the concept of Stateful widgets, how to use them, and practical examples utilizing them.

1. What is State Management?

State management refers to techniques that synchronize an application’s data and UI. The user interface (UI) often changes according to the application’s state, which can be altered by various factors such as user input, network requests, and timers. Flutter provides two main types of widgets to manage this state: Stateful widgets and Stateless widgets.

2. Stateless Widgets and Stateful Widgets

Stateless widgets have immutable states, thus they do not need to be refreshed every time the UI is drawn. In contrast, Stateful widgets can have internal states, and when this state changes, the widget needs to be rebuilt. Generally, Stateful widgets are used in UIs that involve interactions with the user or asynchronous operations.

2.1 Example of Stateless Widget

class MyStatelessWidget extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Text('Hello, world!');
  }
}

2.2 Example of Stateful Widget

class MyStatefulWidget extends StatefulWidget {
  @override
  _MyStatefulWidgetState createState() => _MyStatefulWidgetState();
}

class _MyStatefulWidgetState extends State {
  int _count = 0;

  void _incrementCounter() {
    setState(() {
      _count++;
    });
  }

  @override
  Widget build(BuildContext context) {
    return Column(
      children: [
        Text('You have pushed the button this many times: $_count'),
        ElevatedButton(
          onPressed: _incrementCounter,
          child: Text('Increment'),
        ),
      ],
    );
  }
}

3. Structure of Stateful Widgets

Stateful widgets consist of two classes: a widget class and a state class. The widget class defines the style of the UI that is displayed to the user, while the state class includes mutable data and the logic to change that data. These two classes are closely linked so that when the state in the state class changes, the build method is called to redraw the UI.

4. Lifecycle of Stateful Widgets

Stateful widgets have a specific lifecycle. This lifecycle consists of various methods related to the creation, updating, and deletion of the widget. These methods play an important role in ensuring the efficiency of state management. The main lifecycle methods are as follows:

• createState: Called when the widget is created. It should return a new state object.
• initState: Called for the first time after the state object is created. Suitable for performing initialization tasks.
• didChangeDependencies: Called when the widget’s dependencies change. Mainly used with InheritedWidget.
• build: Used for rendering the UI. The build method of the state object is called every time the state changes.
• setState: Method used to change the state and update the UI.
• dispose: Called when the object’s lifespan ends, used for cleaning up resources.

4.1 Example of State Class Lifecycle

class _MyStatefulWidgetState extends State {
  @override
  void initState() {
    super.initState();
    // Initialization code
  }

  @override
  void didChangeDependencies() {
    super.didChangeDependencies();
    // Dependency change code
  }

  @override
  Widget build(BuildContext context) {
    // UI construction code
  }

  @override
  void dispose() {
    // Resource cleanup code
    super.dispose();
  }
}

5. Real Example of Implementing Stateful Widget

Now let’s learn how to actually implement a Stateful widget. We will create a simple counter application. The functionality will increase the count every time the user clicks the button.

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('Stateful Widget Example'),
        ),
        body: CounterWidget(),
      ),
    );
  }
}

class CounterWidget extends StatefulWidget {
  @override
  _CounterWidgetState createState() => _CounterWidgetState();
}

class _CounterWidgetState extends State {
  int _count = 0;

  void _incrementCounter() {
    setState(() {
      _count++;
    });
  }

  @override
  Widget build(BuildContext context) {
    return Center(
      child: Column(
        mainAxisAlignment: MainAxisAlignment.center,
        children: [
          Text('Press the button to increase the count:'),
          Text('$_count', style: Theme.of(context).textTheme.headline4),
          ElevatedButton(
            onPressed: _incrementCounter,
            child: Text('Increment'),
          ),
        ],
      ),
    );
  }
}

The above code is an implementation of a Stateful widget using the basic structure of Flutter. This application increases the count value every time the ‘Increment’ button is clicked and displays the incremented value on the screen.

6. State Management Patterns

Although Stateful widgets are designed to manage state, more efficient state management patterns may be required in complex applications. There are various state management patterns, and we will introduce the most commonly used patterns here.

6.1 Provider Pattern

Provider is one of the most widely used state management solutions in Flutter. The Provider pattern is based on InheritedWidget and is useful for simply managing and sharing state. Here is the code for the counter example modified to use Provider.

import 'package:flutter/material.dart';
import 'package:provider/provider.dart';

void main() {
  runApp(
    ChangeNotifierProvider(
      create: (context) => Counter(),
      child: MyApp(),
    ),
  );
}

class Counter with ChangeNotifier {
  int _count = 0;

  int get count => _count;

  void increment() {
    _count++;
    notifyListeners(); // Notify state change
  }
}

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

class CounterWidget extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    final counter = Provider.of(context);
    
    return Center(
      child: Column(
        mainAxisAlignment: MainAxisAlignment.center,
        children: [
          Text('Press the button to increase the count:'),
          Text('${counter.count}', style: Theme.of(context).textTheme.headline4),
          ElevatedButton(
            onPressed: counter.increment,
            child: Text('Increment'),
          ),
        ],
      ),
    );
  }
}

6.2 BLoC Pattern

The BLoC (Business Logic Component) pattern is an approach that separates the business logic of the app from the UI. It follows reactive programming and controls data flow using streams. We will cover more about the BLoC pattern in future lectures.

7. Conclusion

In this lecture and example, we explored the structure and lifecycle of Stateful widgets and practical use cases. We learned about the necessity of state management in Flutter and various state management patterns. Stateful widgets are essential elements for building UIs that change through user interactions, and effective use of them can lead to the development of more efficient and maintainable applications.

In future lectures, we will gradually learn about more state management patterns, UI components, application architectures, and more. Create your own amazing applications using Flutter!

Flutter is a UI toolkit developed by Google for creating native compiled applications for mobile, web, and desktop. The biggest feature of Flutter is that it offers excellent performance and powerful UI components. In this course, we will take an in-depth look at Flutter’s element tree. The element tree is one of the core concepts of Flutter UI, playing a crucial role in understanding the structure of the application and the lifecycle of widgets.

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('Element Tree Example'),
        ),
        body: Center(
          child: MyStatefulWidget(),
        ),
      ),
    );
  }
}

class MyStatefulWidget extends StatefulWidget {
  @override
  _MyStatefulWidgetState createState() => _MyStatefulWidgetState();
}

class _MyStatefulWidgetState extends State {
  int _counter = 0;

  void _incrementCounter() {
    setState(() {
      _counter++;
    });
  }

  @override
  Widget build(BuildContext context) {
    return Column(
      mainAxisAlignment: MainAxisAlignment.center,
      children: [
        Text('Press the button to count:', style: TextStyle(fontSize: 20)),
        Text('$_counter', style: TextStyle(fontSize: 40)),
        ElevatedButton(
          onPressed: _incrementCounter,
          child: Text('Increase Count'),
        ),
      ],
    );
  }
}

Hello! In this tutorial, we will take a deep dive into Flutter’s Stateless widgets. Stateless widgets are one of the most fundamental components in Flutter, as they do not hold any state and always provide the same output given the same input. Due to this characteristic, Stateless widgets are very useful in constructing UIs and are efficient and customizable.

Overview of Stateless Widgets

Stateless widgets are used when the data does not change or does not need to change. In other words, these widgets do not store state and always display the same information. These widgets have the following characteristics:

• Immutability: Once a Stateless widget is created, its data cannot be changed.
• Efficiency: Since there is no need to manage state, this widget is lighter and more efficient.
• Simple Reusability: They can be easily reused as they always provide the same output with the same data.

Using Stateless widgets to construct the UI of a Flutter application is simple and intuitive. Now, let’s learn how to create and use Stateless widgets.

Structure of Stateless Widgets

Stateless widgets are created by inheriting from the StatelessWidget class in Flutter. This class overrides the build method to define how the widget will be constructed.

Example of a Stateless Widget

Here is an example of using a basic Stateless widget:

import 'package:flutter/material.dart';

class MyStatelessWidget extends StatelessWidget {
  final String title;

  MyStatelessWidget({Key key, this.title}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return Container(
      padding: EdgeInsets.all(16.0),
      child: Text(
        title,
        style: TextStyle(fontSize: 24),
      ),
    );
  }
}

The above code creates a simple Stateless widget. This widget takes a title parameter and displays it as a Text widget. The build method determines how Flutter visually represents the widget.

Advantages of Stateless Widgets

Using Stateless widgets offers several advantages:

• Performance: You can avoid unnecessary state management, which improves the app’s performance.
• Simplicity: This widget is easy to use and has a simple structure.
• Flexibility: It can be easily integrated into various functional programming styles.

Stateless Widgets vs. Stateful Widgets

The two main types of widgets in Flutter are Stateless widgets and Stateful widgets. Stateless widgets do not hold any state, while Stateful widgets maintain state. To understand this, let’s compare them with a simple example.

Example of a Stateful Widget

class MyStatefulWidget extends StatefulWidget {
  @override
  _MyStatefulWidgetState createState() => _MyStatefulWidgetState();
}

class _MyStatefulWidgetState extends State {
  int counter = 0;

  void incrementCounter() {
    setState(() {
      counter++;
    });
  }

  @override
  Widget build(BuildContext context) {
    return Column(
      children: [
        Text('Counter: $counter'),
        ElevatedButton(
          onPressed: incrementCounter,
          child: Text('Increment'),
        ),
      ],
    );
  }
}

The above Stateful widget increments the value of the counter every time the button is clicked. It updates the state by calling the setState method, which causes the widget to rebuild. In contrast, Stateless widgets cannot change state, so there is no change.

Use Cases for Stateless Widgets

Stateless widgets are primarily used in the following cases:

• Displaying simple information: text, icons, etc.
• Creating static layouts: structuring the layout of widgets when no state is needed
• Combining various UI components: buttons, cards, etc.

Styling in Stateless Widgets

When constructing a UI using Stateless widgets, it is important to understand how to set styles and layouts. In Flutter, you can apply various styling and layouts using widgets like Container, Row, and Column.

Styling Example

class StyledWidget extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Container(
      margin: EdgeInsets.all(20),
      padding: EdgeInsets.all(10),
      decoration: BoxDecoration(
        color: Colors.blue,
        borderRadius: BorderRadius.circular(10),
      ),
      child: Text(
        'Styled Container',
        style: TextStyle(color: Colors.white, fontSize: 20),
      ),
    );
  }
}

In the example above, the Container widget is used to set the background color, margin, padding, and border radius. This creates a styled widget.

Refactoring with Stateless Widgets

Utilizing Stateless widgets can enhance the readability of your code and make maintaining it easier. It is important to refactor Stateless widgets well to increase code reusability, and here are some methods:

• Widgetize: To prevent code duplication, you can separate Stateless widgets into functions based on functionality.
• Use Composition: Combine multiple Stateless widgets to create more complex UIs.
• Clear Naming: Assign appropriate names to widgets to make their purposes clear.

Building an Application Using Stateless Widgets

Now, let’s create a simple Flutter application using Stateless widgets. This application will primarily have a feature to input the user’s name and display that name prominently on the screen.

Application Example Code

import 'package:flutter/material.dart';

void main() {
  runApp(MyApp());
}

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Stateless Widget Demo',
      home: MyHomePage(),
    );
  }
}

class MyHomePage extends StatelessWidget {
  final TextEditingController _controller = TextEditingController();

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('Stateless Widget Example'),
      ),
      body: Padding(
        padding: const EdgeInsets.all(16.0),
        child: Column(
          children: [
            TextField(
              controller: _controller,
              decoration: InputDecoration(labelText: 'Enter your name'),
            ),
            ElevatedButton(
              child: Text('Show Name'),
              onPressed: () {
                final name = _controller.text;
                showDialog(
                  context: context,
                  builder: (BuildContext context) {
                    return AlertDialog(
                      title: Text('Hello, $name!'),
                      actions: [
                        TextButton(
                          child: Text('Close'),
                          onPressed: () {
                            Navigator.of(context).pop();
                          },
                        ),
                      ],
                    );
                  },
                );
              },
            ),
          ],
        ),
      ),
    );
  }
}

The above code creates a basic Flutter application that allows the user to input their name and displays that name in a dialog upon pressing a button. In this example, TextField and ElevatedButton are used to define a simple UI, and Stateless widgets are constructed to respond to user input.

Conclusion

In this tutorial, we have thoroughly explored Flutter’s Stateless widgets. Stateless widgets are powerful tools that can construct UIs efficiently and concisely. By using these widgets when data does not change, you can improve performance and clarify the structure of your code. Leverage Stateless widgets in various scenarios to make your Flutter applications more attractive and functional.

Thank you!

One of the core concepts of programming, inheritance is one of the most important features of object-oriented programming,
and Flutter also follows the principles of object-oriented programming.
In this course, we will explain the concept of inheritance in Flutter, how to use it, and through practical examples,
you will gain a deep understanding of inheritance.

1. Definition of Inheritance

Inheritance refers to the process where a new class (child class or subclass) inherits the properties and
methods of an existing class (parent class or super class). This maximizes code reuse and allows
for easy expression of relationships between classes.

2. Necessity of Inheritance

Inheritance is necessary for the following reasons:

• Code Reuse: By reusing the code that has already been written in a new class,
  it reduces code duplication and makes maintenance easier.
• Maintenance: Changes or bug fixes in the parent class are automatically applied
  to all child classes that inherit from it.
• Hierarchical Structure: It creates a hierarchical structure among related classes
  contributing to the readability of the program.

3. How to Use Inheritance in Flutter

Since Flutter is based on the Dart language, it follows the inheritance implementation of Dart.
To inherit a class in Dart, the `extends` keyword is used.
The basic syntax is as follows.

class Parent {
    void show() {
        print("This is a method of the parent class.");
    }
}

class Child extends Parent {
    void display() {
        print("This is a method of the child class.");
    }
}

In the above example, the `Child` class inherits from the `Parent` class,
allowing it to use the `show()` method while also defining its own
`display()` method.

4. Method Overriding

The process of redefining a parent class method in a child class through inheritance
is called Method Overriding.
This allows the child class to implement the parent class method
in its own way.

class Parent {
    void show() {
        print("Parent class's show()");
    }
}

class Child extends Parent {
    @override
    void show() {
        print("Child class's show()");
    }
}

By using the `@override` keyword, you can explicitly indicate the method you are overriding
that was inherited from the parent class,
thus increasing the clarity of the code.

5. Multiple Inheritance and Mixins

Dart does not support multiple inheritance, but you can
combine multiple classes using mixins. A mixin is
a way to reuse code through classes that are not classes themselves.
To define a mixin, you can use the `mixins` keyword.

mixin MixinA {
    void methodA() {
        print("Method of Mixin A");
    }
}

class Base {}

class Child extends Base with MixinA {
    void methodB() {
        print("Method of the child class");
    }
}

In this example, the `Child` class is able to use
the `methodA()` method through the `MixinA` mixin.
In other words, mixins enable code reuse as an alternative to multiple inheritance.

6. Practical Example: Utilizing Inheritance in Flutter

Now let’s create a simple example that utilizes inheritance
in a Flutter application. Here, we will show how to use
inheritance along with basic UI composition.

import 'package:flutter/material.dart';

void main() {
  runApp(MyApp());
}

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: HomeScreen(),
    );
  }
}

class HomeScreen extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(title: Text('Inheritance Example')),
      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: [
            ChildWidget(),
            SizedBox(height: 20),
            ParentWidget(),
          ],
        ),
      ),
    );
  }
}

class ParentWidget extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Text(
      'This is the parent class.',
      style: TextStyle(fontSize: 24),
    );
  }
}

class ChildWidget extends ParentWidget {
  @override
  Widget build(BuildContext context) {
    return Text(
      'This is the child class.',
      style: TextStyle(fontSize: 24, color: Colors.blue),
    );
  }
}

The above code describes two widget classes.
`ParentWidget` outputs basic text, while
`ChildWidget` inherits from `ParentWidget` and changes
the text color.
This shows how inheritance can be used to change or
extend the properties of UI widgets.

7. Summary

In this lesson, we learned about the concept of inheritance in Flutter and
its necessity, explained the inheritance syntax in Dart,
method overriding, and advanced concepts such as mixins.
We also confirmed how inheritance is utilized through a practical example and
learned how to effectively use inheritance in a Flutter application.

Inheritance is one of the central concepts of object-oriented programming,
and it plays an important role when developing Flutter applications.
In future lessons, we will discuss extending inheritance to develop complex
applications.
We hope this course provides insight into understanding the basic concept of inheritance and
how it can be applied in programming.

In this tutorial, we will learn how to implement animal sounds using Flutter. Animal sounds are commonly used in educational apps for children or games, and adding such features can invigorate the app and enhance the user experience.

1. Project Setup

First, we need to set up a new Flutter project. Open the terminal or command prompt and run the following command to create a new Flutter application:

flutter create animal_sounds

Once the project is created, navigate to that directory:

cd animal_sounds

2. Adding Necessary Packages

We will use the audioplayers package to play animal sounds. This package helps you easily play audio files. Open the pubspec.yaml file and add the following dependency:

dependencies:
  flutter:
    sdk: flutter
  audioplayers: ^0.20.1

After adding the dependency, run the following command in the terminal to install the package:

flutter pub get

3. Understanding Project Structure

Now, let’s understand the project structure. Inside the lib folder, there is a main.dart file. This file is the entry point of the application and is used to define the UI and logic.

4. Building User Interface

To build the UI, modify the main.dart file as follows:

import 'package:flutter/material.dart';
import 'package:audioplayers/audioplayers.dart';

void main() {
  runApp(MyApp());
}

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Animal Sounds',
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: AnimalSoundsPage(),
    );
  }
}

class AnimalSoundsPage extends StatelessWidget {
  final AudioPlayer audioPlayer = AudioPlayer();

  void playSound(String sound) {
    audioPlayer.play(AssetSource(sound));
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('Animal Sounds'),
      ),
      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: [
            ElevatedButton(
              onPressed: () => playSound('sounds/dog_bark.mp3'),
              child: Text('Dog Sound'),
            ),
            ElevatedButton(
              onPressed: () => playSound('sounds/cat_meow.mp3'),
              child: Text('Cat Sound'),
            ),
            ElevatedButton(
              onPressed: () => playSound('sounds/cow_moo.mp3'),
              child: Text('Cow Sound'),
            ),
          ],
        ),
      ),
    );
  }
}

This code creates simple buttons that play the respective animal sound when clicked. Each sound file should be located in the sounds folder, which should be created at the same level as lib.

5. Adding Sound Files

Now, we need to prepare the animal sound files. Find appropriate audio files and save them in the lib/sounds folder with names like dog_bark.mp3, cat_meow.mp3, and cow_moo.mp3.

Once the files are ready, you need to add the file paths to the pubspec.yaml:

flutter:
  assets:
    - sounds/dog_bark.mp3
    - sounds/cat_meow.mp3
    - sounds/cow_moo.mp3

6. Testing Sound Playback

Now, let’s run the project. Use the following command in the terminal to run the application:

flutter run

If the app runs correctly, you will hear the animal sounds when you click each button.

7. Improving the UI

The basic UI works well, but we can improve it to enhance the user experience. For example, adding icons for each animal can make it more intuitive, or you can beautify the sound buttons. Here’s how to add icons to each button:

ElevatedButton.icon(
  onPressed: () => playSound('sounds/dog_bark.mp3'),
  icon: Icon(Icons.pets),
  label: Text('Dog Sound'),
),

8. Adjusting Sound Playback Settings

You can adjust settings like volume, speed, and looping when playing sounds. By using the AudioPlayer instance, you can call various methods for adjustments such as the following:

audioPlayer.setVolume(0.5); // Adjust volume
audioPlayer.setPlaybackRate(1.5); // Adjust playback speed
audioPlayer.setReleaseMode(ReleaseMode.LOOP); // Set loop playback

9. Adding Various Animal Sounds

It’s also a good idea to add more animal sounds to make the app more interesting. Consider adding sounds for birds, lions, tigers, and create buttons that allow users to easily play more sounds.

10. Conclusion and Additional Learning Resources

In this tutorial, we learned how to create a basic app to play animal sounds using Flutter. Through this course, you gained an understanding of Flutter’s audio capabilities and laid the groundwork for adding music and sound effects to your app.

Additionally, I recommend exploring more information through Flutter’s official documentation or various tutorial sites. Flutter is a very flexible and scalable framework, allowing you to add various functionalities based on your creativity.

In the next tutorial, we will delve deeper into other features of Flutter. Thank you!