Flutter – AnimatedBuilder Widget

The AnimatedBuilder widget in Flutter is a powerful utility widget that is used for creating complex animations by rebuilding a part of the widget tree in response to changes in an animation’s value. It is especially useful when you want to animate properties of child widgets that cannot be directly animated using widgets like AnimatedContainer or AnimatedOpacity.In this article, we are going to implement the AnimatedBuilder widget. A sample video is given below to get an idea about what we are going to do in this article.

Basic Syntax of AnimatedBuilder Widget:

Dart

AnimatedBuilder(
  animation: animation, // The animation that triggers rebuilds
  builder: (BuildContext context, Widget? child) {
    return YourAnimatedWidget(); // The widget you want to animate
  },
)

Required Tools

To build this app, you need the following items installed on your machine:

• Visual Studio Code / Android Studio
• Android Emulator / iOS Simulator / Physical Device device.
• Flutter Installed
• Flutter plugin for VS Code / Android Studio.

Step By Step Implementations

Step 1: Create a New Project in Android Studio

To set up Flutter Development on Android Studio please refer to Android Studio Setup for Flutter Development, and then create a new project in Android Studio please refer to Creating a Simple Application in Flutter.

Step 2: Import the Package

First of all import material.dart file.

import 'package:flutter/material.dart';

Step 3: Execute the main Method

Here the execution of our app starts.

Dart

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

Step 4: Create MyApp Class

In this class we are going to implement the MaterialApp , here we are also set the Theme of our App.

Dart

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      theme: ThemeData(
        // Set the app's primary theme color
        primarySwatch: Colors.green,
      ),
      debugShowCheckedModeBanner: false,
      home: AnimatedBuilderExample(),
    );
  }
}

Step 5: Create AnimatedSwitcherExample Class

In this class we are going to Implement the AnimatedBuilder widget that help to create a transition of a container of width and height of 50.0 to 200.0. Comments are added for better understanding.

AnimatedBuilder(
          animation: _controller,
          builder: (BuildContext context, Widget? child) {
            return Container(
              width: _animation.value, // Animate the width
              height: _animation.value, // Animate the height
              color: Colors.green, // Container background color
              child: Center(
                child: Text(
                  'Hello',
                  style: TextStyle(color: Colors.white), // Text color
                ),
              ),
            );
          },
        ),

Dart

class AnimatedBuilderExample extends StatefulWidget {
  @override
  _AnimatedBuilderExampleState createState() => _AnimatedBuilderExampleState();
}

class _AnimatedBuilderExampleState extends State<AnimatedBuilderExample>
    with SingleTickerProviderStateMixin {
  late AnimationController _controller;
  late Animation<double> _animation;

  @override
  void initState() {
    super.initState();
    _controller = AnimationController(
      duration: Duration(seconds: 2), // Animation duration
      vsync: this,
    );
    // Tween animation
    _animation = Tween<double>(begin: 50.0, end: 200.0).animate(_controller);
    _controller.forward(); // Start the animation
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('AnimatedBuilder Demo'), // App bar title
      ),
      body: Center(
        child: AnimatedBuilder(
          animation: _controller,
          builder: (BuildContext context, Widget? child) {
            return Container(
              width: _animation.value, // Animate the width
              height: _animation.value, // Animate the height
              color: Colors.green, // Container background color
              child: Center(
                child: Text(
                  'Hello',
                  style: TextStyle(color: Colors.white), // Text color
                ),
              ),
            );
          },
        ),
      ),
    );
  }

  @override
  void dispose() {
    _controller.dispose(); // Dispose of the animation controller
    super.dispose();
  }
}

Here is the full Code of main.dart file

Dart

import 'package:flutter/material.dart';

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

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      theme: ThemeData(
        primarySwatch: Colors.green, // Set the app's primary theme color
      ),
      debugShowCheckedModeBanner: false,
      home: AnimatedBuilderExample(),
    );
  }
}

class AnimatedBuilderExample extends StatefulWidget {
  @override
  _AnimatedBuilderExampleState createState() => _AnimatedBuilderExampleState();
}

class _AnimatedBuilderExampleState extends State<AnimatedBuilderExample>
    with SingleTickerProviderStateMixin {
  late AnimationController _controller;
  late Animation<double> _animation;

  @override
  void initState() {
    super.initState();
    _controller = AnimationController(
      duration: Duration(seconds: 2), // Animation duration
      vsync: this,
    );
    _animation = Tween<double>(begin: 50.0, end: 200.0).animate(_controller); // Tween animation
    _controller.forward(); // Start the animation
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('AnimatedBuilder Demo'), // App bar title
      ),
      body: Center(
        child: AnimatedBuilder(
          animation: _controller,
          builder: (BuildContext context, Widget? child) {
            return Container(
              width: _animation.value, // Animate the width
              height: _animation.value, // Animate the height
              color: Colors.green, // Container background color
              child: Center(
                child: Text(
                  'Hello',
                  style: TextStyle(color: Colors.white), // Text color
                ),
              ),
            );
          },
        ),
      ),
    );
  }

  @override
  void dispose() {
    _controller.dispose(); // Dispose of the animation controller
    super.dispose();
  }
}

Output: