Getting Started with Flutter Animations Using AnimatedContainer

Introduction

Flutter’s rich set of built-in widgets makes it easy to add motion to your app. Among the simplest yet most powerful is AnimatedContainer. With AnimatedContainer, you can animate changes to its properties—such as width, height, color, padding, and alignment—without writing explicit AnimationController code. In this guide, you’ll learn how to implement Flutter basic animations using AnimatedContainer, covering the essentials of basic Flutter animations and Flutter animation fundamentals. By the end, you’ll have a reusable pattern to add smooth, implicit animations to your UI.

Why AnimatedContainer?

AnimatedContainer is part of Flutter’s family of implicitly animated widgets. Unlike explicit animations where you manually control every frame, AnimatedContainer handles interpolation for you: you only specify the old and new property values plus a duration and curve. This approach enables fast iteration, fewer lines of code, and cleaner state management—ideal for beginner and intermediate developers looking to introduce motion to buttons, cards, or layout changes.

Key benefits of AnimatedContainer:

• Zero boilerplate: no AnimationController, no Tween, no Listeners

• Declarative API: state changes trigger animations automatically

• Flexible: animate multiple properties in one widget

Setting Up Your Project

1. Create a new Flutter app (if you don’t have one already):

flutter create animated_container_demo  
cd animated_container_demo

1. Open lib/main.dart in your IDE.

2. Remove the default counter code and replace it with a StatefulWidget template:

import 'package:flutter/material.dart';

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

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

1. Create an AnimationHomePage StatefulWidget. This will hold the AnimatedContainer and control its state.

Implementing Basic Animation

Inside your AnimationHomePage, you’ll toggle between two sets of property values. When a user taps a button, you call setState and change the target width, height, or color. AnimatedContainer animates from the current value to the new value automatically.

class AnimationHomePage extends StatefulWidget {
  @override
  _AnimationHomePageState createState() => _AnimationHomePageState();
}

class _AnimationHomePageState extends State<AnimationHomePage> {
  double _width = 100;
  double _height = 100;
  Color _color = Colors.blue;

  void _animateContainer() {
    setState(() {
      _width = _width == 100 ? 200 : 100;
      _height = _height == 100 ? 200 : 100;
      _color = _color == Colors.blue ? Colors.green : Colors.blue;
    });
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(title: Text('Flutter Basic Animations')),
      body: Center(
        child: AnimatedContainer(
          width: _width,
          height: _height,
          color: _color,
          duration: Duration(seconds: 1),
          curve: Curves.easeInOut,
        ),
      ),
      floatingActionButton: FloatingActionButton(
        onPressed: _animateContainer,
        child: Icon(Icons.play_arrow),
      ),
    );
  }
}

Explanation:

• width, height, color: the animatable properties.

• duration: how long the animation lasts.

• curve: easing function for smooth motion.

• setState triggers the transition—no manual tweening required.

Customizing Animation Properties

To explore more Flutter animation fundamentals, try adjusting:

• Duration: instant (100ms) vs. slow (2s) effects.

• Curve: experiment with Curves.bounceOut, Curves.elasticIn, or custom curves.

• BorderRadius or padding: animate shape or spacing.

Add a border radius change to animate between a square and circle:

AnimatedContainer(
  width: _width,
  height: _height,
  decoration: BoxDecoration(
    color: _color,
    borderRadius: BorderRadius.circular(_width == 100 ? 0 : 100),
  ),
  duration: Duration(milliseconds: 800),
  curve: Curves.easeInOutBack,
);

This snippet demonstrates animating decoration properties by wrapping the color and borderRadius inside BoxDecoration. You can also chain multiple AnimatedContainers or nest them to build complex scenes with synchronized animations.

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Conclusion

You’ve now mastered the basics of Flutter basic animations with AnimatedContainer. This widget is your go-to solution for quick, declarative, and powerful UI transitions. By understanding how to change properties and trigger setState, you can create engaging interactions without the overhead of explicit animation controllers. Continue exploring other implicitly animated widgets like AnimatedOpacity or AnimatedPositioned to expand your Flutter animation toolkit.